Mosaicism for GNAS methylation defects associated with pseudohypoparathyroidism type 1B arose in early post-zygotic phases
Elli et al. Clinical Epigenetics
Mosaicism for GNAS methylation defects associated with pseudohypoparathyroidism type 1B arose in early post-zygotic phases
Francesca Marta Elli 0
Maura Arosio 0
Anna Spada 0
Giovanna Mantovani 0
0 Endocrinology Unit, Department of Clinical Sciences and Community Health, University of Milan , Via Francesco Sforza, 35-20122 Milan , Italy
Background: Pseudohypoparathyroidism type 1B (PHP1B; MIM#603233) is a rare imprinting disorder (ID), associated with the GNAS locus, characterized by parathyroid hormone (PTH) resistance in the absence of other endocrine or physical abnormalities. Sporadic PHP1B cases, with no known underlying primary genetic lesions, could represent true stochastic errors in early embryonic maintenance of methylation. Previous data confirmed the existence of different degrees of methylation defects associated with PHP1B and suggested the presence of mosaicism, a phenomenon already described in the context of other IDs. Results: With respect to mosaic conditions, the study of multiple tissues is a necessary approach; thus, we investigated somatic cell lines (peripheral blood and buccal epithelium and cells from the urine sediment) descending from different germ layers from 19 PHP patients (11 spor-PHP1B, 4 GNAS mutated PHP1A, and 4 PHP with no GNAS (epi)genetic defects) and 5 healthy controls. We identified 11 patients with epigenetic defects, further subdivided in groups with complete or partial methylation defects. The recurrence of specific patterns of partial methylation defects limited to specific CpGs was confirmed by checking methylation profiles of spor-PHP1B patients diagnosed in our lab (n = 56). Underlying primary genetic defects, such as uniparental disomy or deletion, potentially causative for the detected partial methylation were excluded in all samples. Conclusions: Our data showed no differences of methylation levels between organs and tissues from the same patient, so we concluded that the epimutation occurred in early post-zygotic phases and that the partial defects were mosaics. The number of patients with no detectable (epi)genetic GNAS defects was too small to exclude epimutations occurring in later post-zygotic phases, affecting only selected tissues different from blood, thus leading to underdiagnosis during routine molecular diagnosis. Finally, we found no correlation between methylation ratios, representing the proportion of epimutated cells, and the clinical presentation, further confirming the hypothesis of a threshold effect of the GNAS loss of imprinting leading to an “all-or-none” phenotype.
GNAS; Imprinting; Mosaicism; Pseudohypoparathyroidism; Albright hereditary osteodystrophy; PTH resistance; Epigenetics; Methylation defects
Pseudohypoparathyroidism type 1B (PHP1B; MIM #
603233) is a rare imprinting disorder (ID) characterized
by renal resistance to parathyroid hormone (PTH) in the
absence of other endocrine or physical abnormalities.
Renal resistance to PTH, the hallmark of PHP, was
documented by markedly blunted or absent urinary phosphate
and cAMP responses to PTH injection. More recently,
resistance to the action of thyroid-stimulating hormone
(TSH) has also been described in a large subset of
patients, while growth hormone (GH) secretion appears
to be conserved [
In 2000, the PHP1B phenotype was associated with a
loss of imprinting (LOI), at one or more GNAS
differentially methylated regions (DMRs), which disrupts the
parental-specific expression of its transcripts (the
isolated, at the A/B DMR or the broad, at the NESP
DMR associated with the simultaneous LOM at AS, XL
and A/B DMRs) [
]. The autosomal dominant
maternally transmitted form of the disorder (AD-PHP1B) is
caused by microdeletions of long-range imprinting
control elements (ICRs) that regulate GNAS imprinting
]. Conversely, sporadic PHP1B cases (spor-PHP1B)
present a broad GNAS LOI with no known underlying
genetic lesion; thus, they could represent true stochastic
errors in early embryonic maintenance of methylation
. In a small subset of PHP1B patients, the broad
GNAS LOI resulted to be secondary to a complete or
segmental uniparental disomy (UPD) of chromosome 20
The DNA methylation undergoes a process of erasure,
acquisition, and maintenance during gametogenesis,
then it is maintained during the epigenetic
reprogramming in the pre-implantation embryo, and disruptions in
any of these steps may lead to IDs, resulting in the
aberrant development of embryogenesis, placentation,
and postnatal growth [
The examination of DNA methylation patterns in
embryos and in corresponding sperm samples
demonstrated no methylation errors at tested imprinted loci in
sperm, suggesting that the paternal transmission of
epigenetic abnormalities was unlikely [
protection of imprint marks should mainly rely on maternal
proteins stored in the oocyte before fertilization (i.e.,
DPPA3, ZFP57, TRIM28, and DNMT1 gene products),
because both the oocyte and the embryo are
transcriptionally silent until the zygotic gene activation (ZGA),
which takes place at the late four-cell stage in humans.
This hypothesis was further supported by experiments
in mouse embryos showing that ovarian stimulation
disrupted maternal-effect gene products required for
imprint maintenance [
The phenomenon of epigenetic mosaicism has been
already described in the context of other IDs, such as
Angelman syndrome (AS), Silver–Russell syndrome
(SRS), Beckwith–Wiedemann syndrome (BWS), and
transient neonatal diabetes (TND), and it was proposed
that the absence of maternal gene products could cause
complex chimeras with variable degrees of normally and
aberrantly imprinted cells. Relaxation of IGF2 imprinting
was previously found in BWS and in children with
nonsyndromic somatic overgrowth. In particular, the extent
of and the location of (epi)genetic mosaicism may be
responsible for the phenotype heterogeneity. Additionally,
in most cases of TND, the hypomethylation was mosaic
and more marked in non-leukocyte than in leukocyte
The description of rare cases of monozygotic twins
discordant for the methylation status of specific genes, which
represent examples of post-zygotic epimutations arose
after the twinning event, confirmed the existence of
somatic mosaicism also for epigenetic defects [
Singlecell DNA methylation analysis revealed the presence of
epigenetic chimerism in pre-implantation embryos,
emerging during the early pre-implantation phase of
development, which translated into incomplete methylation
patterns in whole embryos. However, further studies are
needed to conclusively determine the mechanisms
through which such chimerism is established .
Previously published data confirmed the existence of
different degrees of methylation defects associated with
PHP1B and suggested the presence of somatic
mosaicism, with the contribution in a given tissue of both
normal cells and cells with epigenetic defects [
]. Up to now, investigations were conducted on PHP
patients’ DNA samples obtained from a single tissue,
mainly peripheral blood, and no specific study has been
performed to confirm and characterize the mosaicism
associated with partial GNAS imprinting defects.
With respect to mosaic conditions, the study of multiple
tissues is a necessary approach, so we collected the genetic
material of somatic cell lines descending from different
germ layers (ectoderm, mesoderm, and endoderm) that
eventually gives rise to tissues and organs through the
process of organogenesis, and we extensively studied their
genetic and epigenetic status at the GNAS locus in both
PHP patients and healthy controls.
We investigated genomic DNA samples obtained from
different tissues of 5 healthy controls, 1 patient with
PHP1A due to a large GNAS deletion, considered as a
positive reference for methylation studies, and 19 PHP
patients (11 spor-PHP1B, 4 GNAS-mutated PHP1A, and
4 PHP with no GNAS (epi)genetic defects).
Sanger sequencing analysis allowed to detect a point
mutation in Gsα-coding exons in 4 patients (patients
12–15) and to exclude small genetic defects in the 15
other patients and 5 healthy controls. Methylation
analysis identified 11 patients with broad GNAS LOI (raw
methylation ratios in the Additional file 1: Table S1).
The comparison of raw methylation ratios confirmed
the reproducibility and reliability of the methylation
specific–multiplex ligand-dependent probe amplification
(MS-MLPA) assay, allowing data validation for
subsequent statistical analysis. Data obtained from the serial
dilution of a sample with a GNAS maternal deletion
confirmed the ability to detect different levels of
methylation (Fig. 1).
After the analysis of genetic markers upstream and
downstream the GNAS locus to determine whether
UPD could be the primary genetic cause of the LOI, all
cases resulted having at least one heterozygous VNTR in
the 20q region (Additional file 1: Table S2). In patients 2
and 11, we were also able to exclude uniparental
heterodisomy as parent’s DNA was available. The exclusion of
uniparental isodisomy and aneuploidies as causative
genetic aberration further supported that the detection of
partial LOI is derived from the presence of an epigenetic
mosaicism rather than a genetic mosaicism.
Single CpG methylation ratios in the three tissues
(peripheral blood and buccal epithelium and cells from
the urine sediment) were the same for each subject, and
in the subsequent statistical analysis, we considered
mean values (Table 1 and Fig. 2).
As expected, in healthy samples and in PHP patients
affected by GNAS point mutations, the NESP DMR was
hemimethylated on the paternal allele, while AS, XL,
and A/B DMRs on the maternal allele.
The investigation of different tissues of four patients
with no GNAS (epi)genetic defects failed to find an
imprinting defect in cell lineages different from
leucocytes, which could explain the clinical phenotype in the
absence of anomalies in blood samples.
Because of the variability among different CpG
methylation ratios belonging to the same DMR in spor-PHP1B
with respect to negative and positive references (NESP
DMR = 0.97 ± 0.17 (mean of three CpGs), AS DMR =
0.11 ± 0.11 (mean of three CpGs), XL DMR = 0.10 ± 0.11
(mean of four CpGs), and A/B DMR = 0.05 ± 0.10 (mean
of two CpGs)), we considered single CpGs instead of
whole DMRs in the downstream analysis. This
CpGspecific analysis (raw data in the Additional file 1: Table
S1) allowed subdivision of spor-PHP1B patients in two
major groups, one with a “complete” methylation defect
(n = 6) and another with a “partial” methylation defect
(n = 5) (Fig. 3).
The “partial” cluster could be further subdivided for
the presence of a partial methylation defect limited to
specific CpGs. Only one patient (patient 2) showed a
partial methylation defect in all CpGs, with methylation
ratios significantly different (P values < 0.01 or < 0.001)
from the positive deleted control. Conversely, the other
four patients displayed a partial LOM limited to the AS
DMR, the XL DMR, or both the AS and the XL DMRs.
In particular, patient 5 had a partial LOM at the AS
DMR (AS1 = 0.24 ± 0.03 and AS3 = 0.25 ± 0.04) and
patient 1, a partial LOM at the XL DMR (XL1 = 0.22 ±
0.05, XL2 = 0.25 ± 0.04, XL3 = 0.18 ± 0.11, and XL4 =
0.17 ± 0.01), while patients 3 and 4 had a partial LOM at
both AS and XL DMRs (AS1 = 0.21 ± 0.04/0.17 ± 0.02,
AS3 = 0.21 ± 0.06/0.15 ± 0, XL1 = 0.20 ± 0.03/0.17 ± 0.01,
XL2 = 0.22 ± 0.03/0.13 ± 0.01, XL3 = 0.27 ± 0.22/0.13 ±
0.02, and XL4 = 0.24 ± 0.24/0.09 ± 0, respectively)
(Additional file 1: Table S1).
The methylation status of the A/B DMR of partial
patients, with the exception of patient PHP2, resulted
more severely affected by the LOM when compared with
5 5 6 3 3 4 1 8 8 0 6 6 6
D .0 .0 .0 .0 .0 .1 .0 .0 .0 .0 .0 .0 .1
) S 0 0 0 0 0 0 0 0 0 0 0 0 0
AS and XL DMRs, with the exclusion of the AS CpG
number 2 whose methylation ratio was nearly 0 in all
samples. This observation further supported the
hypothesis of the existence of a second independent ICR
regulating their epigenetic status, independently from
the A/B DMR. Moreover, the gain of methylation
(GOM) at the NESP DMR was complete in all partial
samples, except in patient PHP2.
To confirm our findings about “partial LOM”
subclusters, we checked GNAS methylation profiles
obtained from genomic DNA extracted from
peripheral blood samples in our series of spor-PHP1B
patients diagnosed in our lab (n = 56), and we
observed that these patterns of partial LOM were
recurrent. In particular, if we consider the whole cohort of
spor-PHP1B patients (n = 67), we found that the
prevalence of cases with partial epigenetic anomalies
was about 42%: 5 patients had a partial LOM limited
to the AS DMR, 12 patients had a partial LOM
limited to the XL DMR, 5 patients had partial LOMs
at AS and XL DMRs, and 7 patients had partial
methylation defects at all 4 DMRs (Fig. 4).
Finally, we searched for an explanation of the phenotypic
variability, which means the number or severity of
hormonal resistances and the presence of signs of Albright
hereditary osteodystrophy (AHO), according to the methylation
ratio and/or the specific affected CpGs, but we failed to find
any significant difference among patients with or without
AHO rather than with one or more endocrine alterations.
In the present work, we investigated GNAS imprinting
in DNA samples obtained from different tissues of a
small series of PHP patients, as previously published
data confirmed the existence of different degrees of
methylation defects associated with PHP1B and
suggested the presence of epigenetic mosaicism [
The broad GNAS LOI was previously associated with
complete or segmental 20qUPD in small subsets of
patients, but this hypothesis was unlikely in our case
series as all patients were heterozygous for at least one
genetic marker, further supporting the presence of
epigenetic mosaicism in subjects with partial
methylation defects [
To study mosaic conditions, the experimental
approach relies on the analysis of multiple tissues from the
same subject; thus, we collected the genetic material of
cell lines descending from different germ layers
(ectoderm, mesoderm, and endoderm). We did not observe
significant differences in methylation levels in different
tissues from the same patient, so we concluded that the
partial LOI was a mosaic condition due to an
epimutation which occurred in early post-zygotic phases, before
the germ layers’ formation. In particular, in patients with
partial LOI, we determined methylation ratios of
0.15–0.25, consistent with an error in methylation that
occurred at the four- or eight-cell phase, i.e., the phase
during which the post-zygotic genome-wide passive
demethylation takes place [
Following fertilization, parental genomes undergo a
global demethylation to facilitate the remodeling from two
distinct differentiated gamete-specific states to a
pluripotent embryonic state, with the exception of imprinted loci
whose differential methylation is preserved by maternal
zygotic effect genes accumulated during the oocyte
growth. Maternal-effect proteins that protect imprinted
methylation sites during pre-implantation development
identified up to now include developmental
pluripotencyassociated 3 (DPPA3; also called STELLA/PGC7), zinc
finger protein 57 (ZFP57), tripartite motif-containing 28
protein (TRIM28; also called KAP1/TIF1b) and DNA
methyltransferase 1 (DNMT1) [
]. Mutations in
ZFP57 were associated with TND, the first heritable global
ID compatible with life described in humans, and perhaps
additional methylation anomalies of imprinted loci are not
yet described .
Although the underlying molecular cause of
sporPHP1B is not clear, the mosaicism in cases with partial
GNAS methylation defects is consistent with a failure of
methylation maintenance in the early zygote, and a
maternal-effect mutation might be postulated. On the
other hand, in patients affected by complete broad
methylation defects, an imprinting defect originating in
gametes, resulting in unstable methylation of the ICRs
afterwards, could be considered, but further studies to
detect factors associated with the GNAS imprinting
maintenance are needed. Conversely, defects affecting
cells from a specific tissue would derive from molecular
errors during later phases of the embryo development,
but unfortunately, the number of investigated patients
with no detectable GNAS (epi)genetic defects was too
small to fully exclude epimutations occurring in later
Studies in the mouse model performed to investigate
structure and regulation of the GNAS-imprinted cluster
identified 2 candidate ICRs with a different mode of
action, one at exon A/B, acting as an insulator model, and
one covering AS and XL promoters, acting through a
mechanism involving antisense RNAs [
]. The detection
of different patterns of mild epigenetic anomalies in our
patients, in particular, partial LOMs limited to the AS
DMR, the XL DMR, or both AS and XL DMRs associated
with a complete LOM at the A/B DMR, uphold the
assumption that two independent and interacting ICRs
regulate GNAS methylation and highlighted the
hypothesis that different molecular mechanisms might be
involved in the epigenetic dysregulation associated to
PHP1B. Additionally, a recent work published by Court
and colleagues showed that the ICR in the AS-XL region
is not a single regulatory unit and that its two DMRs are
partitioned by an interval of about 200-bp [
]. These data
were in accordance with our finding of patients with
partial LOM limited to the AS DMR or to the XL DMR.
Some DMRs, defined as germline or primary DMRs,
acquire their allelic methylation during gametogenesis
and are stably maintained throughout the post-zygotic
development. Conversely, somatic or secondary DMRs
acquire methylation during development and are
regulated by nearby germline DMRs [
studies found that AS, XL, and A/B DMRs are
germline DMRs and that the AS DMR affects the somatic
NESP DMR methylation status, as its antisense
transcript could act in a similar manner to Air [
]. As a
matter of fact, the isolated LOM at the A/B DMR,
both in sporadic and inherited patients, does not
affect the imprinting of the NESP DMR [
observations further supported this hypothesis
because the GOM at the NESP DMR was complete also
in partial patients, except for patient 2, who displayed
a complete LOM at the CpG AS2, raising the possibility
that this region contains a cis-acting sequence involved in
the NESP DMR methylation establishment.
Finally, in our previous work, conducted in 63 patients
with PHP type 1 and GNAS imprinting defects, we
found no correlation between the degree of methylation
defects and the severity of clinical parameters [
absence of correlation between methylation ratios and
the phenotype observed in the present study further
confirms our previous findings and can be explained by
a threshold effect leading to an “all-or-none” phenotype.
To conclude, further studies to unravel the mechanisms
underlying GNAS LOI are needed and, in particular, it will
be crucial to determine whether GNAS LOI in
sporPHP1B patients is associated with a primary or secondary
epigenetic defect, with the final aim to correctly evaluate
the recurrence risk of this imprinting syndrome.
The present study included 5 healthy controls, 1 subject
affected by a whole GNAS locus deletion (g.56′657′
752_59′228′953del, previously described in reference
34), used as positive reference for methylation defects at
GNAS DMRs, and 19 PHP patients (11 with methylation
defects at the GNAS locus, 4 with point mutations in
GNAS Gsα-coding exons, and 4 with no GNAS/PDE4D/
PRKAR1A (epi)genetic defects and no deletions of the
long arm of chromosome 2). Some of these PHP patients
(1–6, 9–10, 12–14, and 16–17) were presented in our
previous works [
25, 28, 29, 31
]. The clinical diagnosis
was based upon the presence or absence of specific
clinical and biochemical signs, i.e., hypocalcemia,
hyperphosphatemia, and raised serum PTH levels in the absence
of vitamin D deficiency and/or typical AHO
manifestations, considered major and minor criteria for the
diagnosis of PHP [
]. Clinical details, including some
additional patient-specific features, and molecular
diagnosis are summarized in Table 2. Informed consent for
genetic and epigenetic studies was obtained from all
subjects involved in the study.
Genomic DNA was extracted from samples of the
peripheral blood (Nucleon BACC2 genomic DNA
purification kit, cod.RPN8502, GE Healthcare), saliva, and
urine (Puregene Core kit, cod. 158622, Qiagen), in
order to obtain the genetic material from somatic cell
lines descending from different germ layers. Buccal
epithelial cells are of ectodermal derivation and urine
sediment cells are derived from the mesoderm, while
leukocytes are from the endoderm. Mutation analysis
was performed by direct sequencing
(BigDye™Terminator v3.1 Cycle Sequencing Kit, cod.4337456, Applied
Age (years at diagnosis)
PTH PTH serum levels, normal range 10–65 pg/mL, TSH TSH serum levels, normal range 0.4–3.9 mU/L, X elevated, but value not available, Ob obesity, RF round
face, MR/BD mental retardation and/or behavioral defects, Br brachydactyly, OS ectopic ossifications, SS short stature, LGA large for gestational age
Biosystems) of GNAS 1–13 exons and flanking intronic
sequences (ENSEMBL ID: ENSG00000087460).
Informative genetic markers in the 20q region were evaluated
to exclude a possible misdiagnosis of spor-PHP1B in
the presence of aneuploidies (monosomy or trisomy) or
uniparental disomy (UPD). According to sample
availability, the analysis was performed in blood, saliva, and
urine samples. For variable number tandem repeat
(VNTR) genotyping, we set up a cost-effective
threeprimer approach based on the simultaneous use of a
couple of sequence-specific primers, the reverse one
containing a poliA tail at the 5′ end to allow easier
allele scoring, associated with a fluorescently labeled
universal forward M13-tailed FAM oligonucleotide. All
primers and experimental conditions are available upon
request. Copy number variant (CNV) analysis of STX16
and GNAS loci and methylation analysis of GNAS
DMRs were performed by MS-MLPA (cod.
ME031100R+ EK1-FAM, MRC-Holland) (methylation-specific
probe location, GR37/hg19, summarized in
Additional file 1: Figure S1). MS-MLPA data analysis was
performed using the Coffalyser.Net (MRC-Holland).
The detection of expected MS-MLPA methylation
ratios of about 0.5 reflected a normal hemimethylated
status in healthy controls (considered as a negative
reference), while finding of MS-MLPA methylation ratios
of about 1 and 0 reflected the apparent LOI in the
GNAS-locus-deleted subject (considered as positive
reference). At least two technical replicates were
performed for each biological sample. A serial dilution, in
triplicate, of GNAS-deleted DNA (0, 12.5, 25, 37.5, 50,
62.5, 75, 87.5, and 100%) in wild type DNA was created
to define the MS-MLPA detection range of different
percentages of epigenetic mosaics. Statistical analysis
was performed using GraphPad Prism version 5 for
Windows (www.graphpad.com). The exploratory data
analysis included means ± SD, median, and interquartile
ranges for values measured in the blood, saliva, and
urine. Based on data distribution, means ± SD were
used for further comparisons. One-way ANOVA with
Bonferroni’s Multiple Comparison test was used to
evaluate the intercluster variability at single CpGs. After
Bonferroni correction, a P value < 0.05 was deemed to
indicate statistical significance. Continuous variables, i.e.,
hormonal and biochemical parameters, were reported as
means ± SD, whereas dichotomous variables, i.e., the
presence of AHO signs, were expressed as proportions.
Differences between means and proportions were checked by
Student’s t and chi-squared tests, respectively. In
particular, for the epigenotype–phenotype correlation
investigation, we considered the following clinical parameters: the
precocity of the disease (defined as the age at diagnosis),
the severity of hormonal resistances (defined as PTH,
calcium, phosphorus, and TSH levels at diagnosis), and the
severity of AHO, defined as the number of AHO signs.
Additional file 1: Figure S1. Methylation-specific probes location,
GR37/hg19. Table S1. Raw methylation ratios. Table S2. Variable number
tandem repeats (VNTRs) in the 20q region analysed to exclude
uniparental disomy (UPD). (DOCX 378 kb)
AHO: Albright hereditary osteodystrophy; AS: Angelman syndrome;
BWS: Beckwith–Wiedemann syndrome; cAMP: Cyclic adenosine
monophosphate; DMRs: Differentially methylated regions; GH: Growth
hormone; GOM: Gain of methylation; Gsα: Alpha subunit of the stimulatory G
protein; ICRs: Imprinting control elements; ID: Imprinting disorder; LOI: Loss
of imprinting; LOM: Loss of methylation; MS-MLPA: Methylation-specific–
multiplex ligand-dependent probe amplification;
PHP: Pseudohypoparathyroidism; PTH: Parathyroid hormone; SD: Standard
deviation; SRS: Silver–Russell syndrome; TND: Transient neonatal diabetes;
TSH: Thyroid-stimulating hormone; UPD: Uniparental disomy; VNTR: Variable
number tandem repeat; ZGA: Zygotic gene activation
The authors are members of and acknowledge the
EuroPseudohypoparathyroidism network (EuroPHP) and the EUCID.net (COST
action BM1208 on imprinting disorders; www.imprinting-disorders.eu).
This work was supported by the Italian Ministry of Health under Grant
GR2009-1608394, Fondazione IRCCS Ca’ Granda Policlinico Ospedale Maggiore
under Grant Ricerca Corrente Funds.
Availability of data and materials
Data generated and/or analyzed during this study are included in this
published article and its supplementary information files, and they are
available from the corresponding author on reasonable request.
FMC conceived and designed the project, analyzed and interpreted the data,
and was a major contributor in writing the manuscript. PB acquired and
analyzed the data. GM conceived and designed the project, followed
patients, interpreted the data, and was a major contributor in writing the
manuscript. AS and MA conceived the project, followed patients, and were
minor contributors in writing the manuscript. All authors read and approved
the final manuscript.
Ethics approval and consent to participate
Informed consent was obtained from all patients (or legal guardians for
minors) and relatives included in the present study. All procedures were
performed in compliance with relevant legislation and institutional
Consent for publication
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
1Endocrinology Unit, Department of Clinical Sciences and Community
Health, University of Milan, Via Francesco Sforza, 35-20122 Milan, Italy.
2Endocrinology and Metabolic Diseases Unit, Fondazione IRCCS Ca’ Granda
Ospedale Maggiore Policlinico, Milan, Italy.
Submit your next manuscript to BioMed Central
and we will help you at every step:
1. Barret D , Breslau NA , Wax MB , Molinoff PB , Downs RW Jr. New form of pseudohypoparathyroidism with abnormal catalytic adenylate cyclase . Am J Phys . 1989 ; 257 ( 2 Pt 1 ): E277 - 83 .
2. Liu J , Litman D , Rosenberg MJ , Yu S , Biesecker LG , Weinstein LS . A GNAS1 imprinting defect in pseudohypoparathyroidism type IB . J Clin Invest . 2000 ; 106 ( 9 ): 1167 - 74 .
3. Mantovani G , Bondioni S , Linglart A , Maghnie M , Cisternino M , Corbetta S , Lania AG , Beck-Peccoz P , Spada A . Genetic analysis and evaluation of resistance to thyrotropin and growth hormone-releasing hormone in pseudohypoparathyroidism type Ib . J Clin Endocrinol Metab . 2007 ; 92 : 3738 - 42 .
4. Bastepe M , Frohlich LF , Hendy GN , Indridason OS , Josse RG , Koshiyama H , Korkko J , Nakamoto JM , Rosenbloom AL , Slyper AH , et al. Autosomal dominant pseudohypoparathyroidism type Ib is associated with a heterozygous microdeletion that likely disrupts a putative imprinting control element of GNAS . J Clin Invest . 2003 ; 112 ( 8 ): 1255 - 63 .
5. Bastepe M , Frohlich LF , Linglart A , Abu-Zara HS , Tojo K , Ward LM , Juppner H . Deletion of the NESP55 differentially methylated region causes loss of maternal GNAS imprints and pseudohypoparathyroidism type Ib . Nat Genet . 2005 ; 37 ( 1 ): 25 - 7 .
6. Linglart A , Gensure RC , Olney RC , Juppner H , Bastepe M. A novel STX16 deletion in autosomal dominant pseudohypoparathyroidism type Ib redefines the boundaries of a cis-acting imprinting control element of GNAS . Am J Hum Genet . 2005 ; 76 ( 5 ): 804 - 14 .
7. Chillambhi S , Turan S , Hwang D , Chen H , Juppner H , Bastepe M. Deletion of the noncoding GNAS antisense transcript causes pseudohypoparathyroidism type Ib and biparental defects of GNAS methylation in cis . J Clin Endocrinol Metab . 2010 ; 95 ( 8 ): 3993 - 4002 . https:// doi.org/10.1210/jc.2009- 2205 .
8. Richard N , Abeguilè G , Coudray N , Mittre H , Gruchy N , Andrieux J , Cathebras P , Kottler M. A new deletion ablating NESP55 causes loss of maternal imprint of A/B GNAS and autosomal dominant pseudohypoparathyroidism type Ib . J Clin Endocrinol Metab . 2012 ; 97 ( 5 ): E863 - 7 . https://doi.org/10.1210/ jc.2011- 2804 .
9. Elli FM , de Sanctis L , Peverelli E , Bordogna P , Pivetta B , Miolo G , Beck-Peccoz P , Spada A , Mantovani G . Autosomal dominant pseudohypoparathyroidism type Ib: a novel inherited deletion ablating STX16 causes loss of imprinting at the A/B DMR . J Clin Endocrinol Metab . 2014 ; 99 ( 4 ): E724 - 8 . https://doi.org/ 10.1210/jc.2013- 3704 .
10. Garin I , Mantovani G , Aguirre U , Barlier A , Brix B , Elli FM , Freson K , Grybek V , Izzi B , Linglart A , de Nanclares GP , Silve C , Thiele S , Werner R . European guidance for the molecular diagnosis of pseudohypoparathyroidism not caused by point genetic variants at GNAS : an EQA study . Eur J Hum Genet . 2015 ; 23 ( 4 ): 560 . https://doi.org/10.1038/ejhg. 2015 . 40 .
11. Bastepe M , Lane AH , Jüppner H . Paternal uniparental isodisomy of chromosome 20q-and the resulting changes in GNAS1 methylation-as a plausible cause of pseudohypoparathyroidism . Am J Hum Genet . 2001 ; 68 ( 5 ): 1283 - 9 .
12. Dixit A , Chandler KE , Lever M , Poole RL , Bullman H , Mughal MZ , Steggall M , Suri M. Pseudohypoparathyroidism type 1b due to paternal uniparental disomy of chromosome 20q . J Clin Endocrinol Metab . 2013 ; 98 ( 1 ): E103 - 8 . https://doi.org/10.1210/jc.2012- 2639 .
13. Reik W , Dean W , Walter J . Epigenetic reprogramming in mammalian development . Science . 2001 ; 293 ( 5532 ): 1089 - 93 .
14. Morgan HD , Santos F , Green K , Dean W , Reik W. Epigenetic reprogramming in mammals . Hum Mol Genet . 2005 ; 14 : R47 - 58 .
15. Shi L , Wu J . Epigenetic regulation in mammalian preimplantation embryo development . Reprod Biol Endocrinol . 2009 ; 7 : 59 . https://doi.org/10.1186/ 1477 -7827-7-59.
16. Shi X , Chen S , Zheng H , Wang L , Wu Y . Abnormal DNA methylation of imprinted loci in human preimplantation embryos . Reprod Sci . 2014 ; 21 ( 8 ): 978 - 83 .
17. Denomme MM , Mann MR . Maternal control of genomic imprint maintenance . Reprod BioMed Online . 2013 ; 27 ( 6 ): 629 - 36 . https://doi.org/10. 1016/j.rbmo. 2013 . 06 .004.
18. Okamoto K , Morison IM , Taniguchi T , Reeve AE . Epigenetic changes at the insulin-like growth factor II/H19 locus in developing kidney is an early event in Wilms tumorigenesis . Proc Natl Acad Sci U S A . 1997 ; 94 ( 10 ): 5367 - 71 .
19. Itoh N , Becroft DM , Reeve AE , Morison IM . Proportion of cells with paternal 11p15 uniparental disomy correlates with organ enlargement in Wiedemann-Beckwith syndrome . Am J Med Genet . 2000 ; 92 ( 2 ): 111 - 6 .
20. Mackay DJ , Boonen SE , Clayton-Smith J , Goodship J , Hahnemann JM , Kant SG , Njølstad PR , Robin NH , Robinson DO , Siebert R , et al. A maternal hypomethylation syndrome presenting as transient neonatal diabetes mellitus . Hum Genet . 2006 ; 120 ( 2 ): 262 - 9 .
21. Galetzka D , Hansmann T , El Hajj N , Weis E , Irmscher B , Ludwig M , SchneiderRätzke B , Kohlschmidt N , Beyer V , Bartsch O , et al. Monozygotic twins discordant for constitutive BRCA1 promoter methylation, childhood cancer and secondary cancer . Epigenetics . 2012 ; 7 ( 1 ): 47 - 54 . https://doi.org/10.4161/ epi.7.1.18814.
22. Bliek J , Alders M , Maas SM , Oostra RJ , Mackay DM , van der Lip K , Callaway JL , Brooks A , van 't Padje S , Westerveld A , et al. Lessons from BWS twins: complex maternal and paternal hypomethylation and a common source of haematopoietic stem cells . Eur J Hum Genet . 2009 ; 17 ( 12 ): 1625 - 34 . https:// doi.org/10.1038/ejhg. 2009 . 77 .
23. Lorthongpanich C , Cheow LF , Balu S , Quake SR , Knowles BB , Burkholder WF , Solter D , Messerschmidt DM . Single-cell DNA-methylation analysis reveals epigenetic chimerism in preimplantation embryos . Science . 2013 ; 341 ( 6150 ): 1110 - 2 . https://doi.org/10.1126/science.1240617.
24. Maupetit-Mehouas S , Mariot V , Reynes C , Bertrand G , Feillet F , Carel JC , Simon D , Bihan H , Gajdos V , Devouge E , et al. Quantification of the methylation at the GNAS locus identifies subtypes of sporadic pseudohypoparathyroidism type Ib . J Med Genet . 2011 ; 48 ( 1 ): 55 - 63 . https:// doi.org/10.1136/jmg. 2010 . 081356 .
25. Elli FM , de Sanctis L , Bollati V , Tarantini L , Filopanti M , Barbieri AM , Peverelli E , Beck-Peccoz P , Spada A , Mantovani G . Quantitative analysis of methylation defects and correlation with clinical characteristics in patients with pseudohypoparathyroidism type I and GNAS epigenetic alterations . J Clin Endocrinol Metab . 2014 ; 99 ( 3 ): E508 - 17 . https://doi.org/10.1210/jc.2013- 3086 .
26. Mackay DJ , Callaway JL , Marks SM , White HE , Acerini CL , Boonen SE , Dayanikli P , Firth HV , Goodship JA , Haemers AP , et al. Hypomethylation of multiple imprinted loci in individuals with transient neonatal diabetes is associated with mutations in ZFP57 . Nat Genet . 2008 ; 40 ( 8 ): 949 - 51 . https:// doi.org/10.1038/ng.187.
27. Williamson CM , Ball ST , Nottingham WT , Skinner JA , Plagge A , Turner MD , Powles N , Hough T , Papworth D , Fraser WD , et al. A cis-acting control region is required exclusively for the tissue-specific imprinting of Gnas . Nat Genet . 2004 ; 36 ( 8 ): 894 - 9 .
28. Court F , Tayama C , Romanelli V , Martin-Trujillo A , Iglesias-Platas I , Okamura K , Sugahara N , Simón C , Moore H , Harness JV , et al. Genome-wide parent-of-origin DNA methylation analysis reveals the intricacies of human imprinting and suggests a germline methylation-independent mechanism of establishment . Genome Res . 2014 ; 24 ( 4 ): 554 - 69 . https://doi.org/10.1101/gr.164913.113.
29. Hayward BE , Bonthron DT . An imprinted antisense transcript at the human GNAS1 locus . Hum Mol Genet . 2000 ; 9 ( 5 ): 835 - 41 .
30. Elli FM , Linglart A , Garin I , de Sanctis L , Bordogna P , Grybek V , Pereda A , Giachero F , Verrua E , Hanna P , Mantovani G , Perez de Nanclares G. The prevalence of GNAS deficiency-related diseases in a large cohort of patients characterized by the EuroPHP Network . J Clin Endocrinol Metab . 2016 ; 101 ( 10 ): 3657 - 68 .
31. Garin I , Elli FM , Linglart A , Silve C , de Sanctis L , Bordogna P , Pereda A , Clarke JT , Kannengiesser C , Coutant R , Tenebaum-Rakover Y , Admoni O , de Nanclares GP , Mantovani G . Novel microdeletions affecting the GNAS locus in pseudohypoparathyroidism: characterization of the underlying mechanisms . J Clin Endocrinol Metab . 2015 ; 100 ( 4 ): E681 - 7 . https://doi.org/10. 1210/jc.2014- 3098 .
32. Elli FM , deSanctis L , Ceoloni B , Barbieri AM , Bordogna P , Beck-Peccoz P , Spada A , Mantovani G . Pseudohypoparathyroidism type Ia and pseudopseudohypoparathyroidism: the growing spectrum of GNAS inactivating mutations . Hum Mutat . 2013 ; 34 ( 3 ): 411 - 6 .
33. Elli FM , Bordogna P , de Sanctis L , Giachero F , Verrua E , Segni M , Mazzanti L , Boldrin V , Toromanovic A , Spada A , et al. Screening of PRKAR1A and PDE4D in a large Italian series of patients clinically diagnosed with Albright hereditary osteodystrophy and/or pseudohypoparathyroidism . J Bone Miner Res . 2016 ; 31 ( 6 ): 1215 - 24 . https://doi.org/10.1002/jbmr.2785.
34. Mantovani G , Spada A , Elli FM . Pseudohypoparathyroidism and Gsα-cAMPlinked disorders: current view and open issues . Nat Rev Endocrinol . 2016 ; 12 ( 6 ): 347 - 56 . https://doi.org/10.1038/nrendo. 2016 . 52 .
35. Thiele S , Mantovani G , Barlier A , Boldrin V , Bordogna P , De Sanctis L , Elli FM , Freson K , Garin I , Grybek V , et al. From pseudohypoparathyroidism to inactivating PTH/PTHrP signalling disorder (iPPSD), a novel classification proposed by the EuroPHP network . Eur J Endocrinol . 2016 ; 175 ( 6 ): P1 - P17 .