A Novel Nonsense Mutation of the GPR143 Gene Identified in a Chinese Pedigree with Ocular Albinism
et al. (2012) A Novel Nonsense Mutation of the GPR143 Gene Identified in a Chinese Pedigree with Ocular
Albinism. PLoS ONE 7(8): e43177. doi:10.1371/journal.pone.0043177
A Novel Nonsense Mutation of the GPR143 Gene Identified in a Chinese Pedigree with Ocular Albinism
Naihong Yan 0
Xuan Liao 0
Su-ping Cai 0
Changjun Lan 0
Yun Wang 0
Xiaomin Zhou 0
Yan Yin 0
Wenhan Yu 0
Xuyang Liu 0
Andreas R. Janecke, Innsbruck Medical University, Austria
0 1 State Key Laboratory of Biotherapy , Ophthalmic Laboratories , Department of Ophthalmology, Translational Neuroscience Center, West China Hospital, Sichuan University , Chengdu , People's Republic of China, 2 Department of Ophthalmology, North Sichuan Medical College , Nanchong , People's Republic of China, 3 Shenzhen Eye Hospital, Jinan University , Shenzhen , People's Republic of China
Background: The purpose of this study was to elucidate the molecular basis of ocular albinism type I in a Chinese pedigree. Methodology/Principal Findings: Complete ophthalmologic examinations were performed on 4 patients, 7 carriers and 17 unaffected individuals in this five-generation family. All coding exons of four-point-one (4.1), ezrin, radixin, moesin (FERM) domain-containing 7 (FRMD7) and G protein-coupled receptor 143 (GPR143) genes were amplified by polymerase chain reaction (PCR), sequenced and compared with a reference database. Ocular albinism and nystagmus were found in all patients of this family. Macular hypoplasia was present in the patients including the proband. A novel nonsense hemizygous mutation c.807T.A in the GPR143 gene was identified in four patients and the heterozygous mutation was found in seven asymptomatic individuals. This mutation is a substitution of tyrosine for adenine which leads to a premature stop codon at position 269 (p.Y269X) of GPR143. Conclusions/Significance: This is the first report that p.Y269X mutation of GPR143 gene is responsible for the pathogenesis of familial ocular albinism. These results expand the mutation spectrum of GPR143, and demonstrate the clinical characteristics of ocular albinism type I in Chinese population.
. These authors contributed equally to this work.
Nystagmus is a common symptom of a range of diseases
including at least three X-linked disorders, with one of those being
ocular albinism type 1 (OA1; MIM 300500) mapped to Xp22.3
. It should be distinguished from the congenital motor
nystagmus (CMN), a hereditary disorder characterized by bilateral
ocular oscillations that occurs in the absence of any obvious ocular
disorders . Identification of the underlying disease of CMN
often requires extensive clinical, electrophysiological,
psychophysical, and eventually molecular genetic examinations, especially
when clinical findings are unrevealing [3,4]. The prevalence of
Xlinked OA1 is estimated to be 1 in 50,000 live births. Most male
patients with OA1 showed normal skin and hair pigment, but will
usually have signs and symptoms of ocular albinism, including
nystagmus, poor visual acuity, iris translucency, foveal hypoplasia
and albinotic fundus [5,6]. However, the characteristics of OA1
have not been well defined in Asians. OA1 is caused by mutations
in the G protein-coupled receptor 143 (GPR143) gene, originally
also known as the OA1 gene . Various types of mutations in
GPR143 have been identified in different countries, but X-linked
OA1 in the Chinese population was rarely reported .
In the present study, a five-generation Chinese family with
OA1was recruited. All affected individuals exhibited nystagmus as
the main symptom and failed to show photophobia, iris
translucency and strabismus. This pedigree was initially
considered as congenital nystagmus. Diagnosis of OA1was made by
extensive clinical examinations. Four-point-one (4.1), ezrin,
radixin, moesin (FERM) domain-containing 7 (FRMD7 candidate
gene for CMN) and G protein-coupled receptor 143 (GPR143,
candidate gene for OA 1) genes were analyzed.
A five-generation Chinese family with OA1 was recruited in
Sichuan (Figure 1). Written informed consent was obtained in
accordance with the Declaration of Helsinki before blood samples
were taken for analysis (see attachment for details). Three minors
were used in this study. Written informed consent was obtained
from the guardians on behalf of the minors (see attachment for
details). This study was approved by both West China Hospital,
Sichuan University Institute Review Board and North Sichuan
Medical College Institute Review Board.
Annealing temperature (6C)
Product size (bp)
Annealing temperature (6C)
Product size (bp)
ATGGTCCCTTCCAAGCGAGT GTTCACATGAGAGGTGCTGCT ACTCCATGCACTGAATACTGA GGATGTGGACCTTACACTTACT
and analyzed with the DNAStar (Madison, WI) software and
compared with the published FRMD7 and GPR143 sequences.
Mutation was named according to the nomenclature
recommended by the Human Genomic Variation Society (HGVS).
In this five-generation Chinese family, the disease was
transmitted from female carrier to affected son, indicating that
the disease was inherited in an X-linked recessive pattern
(Figure 1). The clinical characteristics of OA1 in this pedigree
are described as in Table 2, Figure 2 and 3.
Reduced Visual Acuity and Nystagmus
All four patients presented with nystagmus and reduced visual
acuity (corrected visual acuity of 0.010.2). The nystagmus was
present during their first three months after birth. Eye movement
recording revealed that the patients had conjugate horizontal
nystagmus. The proband (patient III:30, Figure 1), a
forty-twoyear-old male, presented with nystagmus with best corrected visual
acuity being 0.2 OD and 0.2 OS. He presented with nystagmus
and congenital cataract on the fortieth day after birth and
underwent cataract extraction and intraocular lens implantation at
the age of 41. No pigmentation abnormality of skin and hair was
observed in the participants. Ocular abnormalities were not found
in other asymptomatic members examined in this family.
Complete physical examination and detailed ophthalmological
examination were carried out on the subjects of this family,
including 4 affected patients, 7 carriers and some asymptomatic
individuals. Visual acuity (VA) was measured using the
bestcorrected Snellen visual acuity test. Fundus and OCT
examinations were performed using fundus camera (nonmyd WX 3D,
Kowa, Japan) and Spectralis OCT (Heidelberg Engineering,
Mutation Screening and Sequence Analysis
Genomic DNA was extracted from 200 ml of peripheral blood
using the standard phenol/chloroform method. DNA integrity was
evaluated by 1% agarose gel electrophoresis.
Mutation analysis of FRMD7 and GPR143 was performed using
PCR and direct sequencing. Primers were designed to cover the
sequences of all coding exons of the genes, according to published
primer sequences with some modification (Table 1) [9,10]. The
primers were synthesized by Invitrogen (Carlsbad, CA, USA).
PCRs were carried out in a MyCycler thermocycler (Bio-Rad,
Hercules, CA, USA) using the following program: initial
denaturation at 95uC for 2 min followed by 35 cycles of 94uC
for 10s, 54uC56uC for 30s, and 72u for 1 min, and then a final
extension at 72uC for 5 min.
PCR products were directly sequenced using an ABI 377XL
automated DNA sequencer (Applied Biosystems, Foster City, CA),
Fundus Fundus foveal
Yes (High myopia)
Presence of Hypopigmentation in the Fundus and Foveal
Compared with normal individuals (Figure 2, I, J), the patients
(III:19, IV:19) exhibited an albinotic fundus (Figure 2, A, B, C, D,
E, F). All of the patients had foveal hypoplasia. The OCT showed
extension of all neurosensory retinal layers through the area in
which the fovea would normally be located (Figure 3). The clinical
features of affected males and female carriers were shown in
GPR143 Mutation Identification and Analysis
A novel nonsense mutation, c.807T.A, at codon 807 (TAT to
TAA) of exon 7 in GPR143 gene was identified in all affected
males. This mutation was presented as heterozygous in all obligate
female carriers, and it was not found in normal members of the
family. The c.807T.A mutation caused a substitution of tyrosine
leading to a premature termination codon at position 269
(p.Y269X) of GPR143 protein.
A Chinese family with congenital nystagmus as the main
symptom was reported in this study. There is no difference in iris
pigmentation between patients (except the proband) or carriers
and normal individuals in this family. The patients presented with
only mild hypopigmentation in fundus. The presence of foveal
hypoplasia could be ignored since the macular morphology could
not be easily obtained by OCT due to the poor fixation of the
nystagmus eye of the patients. Therefore this Chinese family was
considered originally as congenital nystagmus. Preising et al.
reported that nystagmus, macular hypoplasia and
hypopigmentation of the fundus were the characteristic signs of ocular albinism
which are more reliable in identifying patients with albinism
For the molecular diagnosis of this pedigree, the FRMD7 gene
(candidate gene for congenital nystagmus) and GPR143 gene
(candidate gene for OA1) were analyzed. The sequence analysis of
GPR143 demonstrated a novel nonsense mutation (p.Y269X) in
exon 7. All affected males were hemizygous for the mutation and
female carriers were heterozygous for the mutation whereas the
other normal members of the family had no mutation. Another
gene, FRMD7, involved in the development of congenital
nystagmus, was screened and no mutation was found. Thus, the
results of clinical and genetic findings provide solid evidence
showing that this Chinese family has X-linked OA1, and the
p.Y269X mutation of GPR143 is responsible for the pathogenesis.
Bassi et al. (1995) cloned GPR143 gene for ocular albinism type 1
from the distal short arm of the X chromosome . Also in 1995,
Schiaffino et al. screened GPR143 gene and detected various
mutations in one-third of X-linked ocular albinism (XLOA)
patients . To date, about one hundred mutations of GPR143
were deposited in Human Gene Mutation Database (HGMD),
including deletion, frameshift, and nonsense mutations. Most of
GPR143 mutations were reported in a large collection of patients
mainly with ocular albinism [12,13,14,15]. In 2001, Preising et al.
reported an X-linked CN family with ocular albinism and found
14 bp deletion in GPR143 gene . In 2007, Liu et al. identified a
novel missense GPR143 mutation in a large Chinese family with
CN as the most prominent and consistent manifestation . In
more recent years, GPR143 mutations have been identified in the
other two Chinese families with X -linked CN without any classical
phenotype of OA1. One family had a 37 bp deletion mutation in
exon 1 of GPR143 . The other family had a 19 bp duplication
in exon 1 of GPR143 and all affected individuals exhibited
nystagmus . These two reports did not present sufficient
clinical data to evaluate their hypothesis of isolated nystagmus
from GPR143 variants. Preising et al. suggested male patients with
congenital nystagmus were candidates for X-linked OA and a
thorough clinical examination was needed . Furthermore,
analysis of the FRMD7 and GPR143 genes would be helpful to
distinguish these two conditions from the molecular level.
GPR143 on chromosome Xp22.3 contains 9 exons and encodes
a protein of 404 amino acids containing seven putative
transmembrane domains and one potential N-glycosylation site
using an asparagine at codon 106 . GPR143 protein is a
conserved integral membrane protein that has weak similarities to
G protein-coupled receptors (GPCRs), which participate in the
most common signal transduction system at the plasma
membrane. It binds heterotrimeric G proteins, which suggests that
GPR143 GPCR-mediated signal transduction systems also operate
at the internal membranes in mammalian cells . The p.Y269X
mutation identified in our study was predicted to result in a
truncated protein with 269 amino acids shorter than the normal
full-length protein, suggesting that this is a loss-of-function
mutation. Furthermore, the mutated transcript is likely to be
degraded by the nonsense-mediated mRNA decay (NMD)
pathway. This hypothesis assumed that the truncated protein
may not even be produced.
It is unclear how the mutated GPR143 causes the ocular
abnormalities, such as macular hypoplasia in people with ocular
albinism. Lopez et al. proposed that L-3, 4-dihydroxyphenylalanine
(L-DOPA) might be a ligand for the protein encoded by GPR143
. L-DOPA is a precursor in melanin synthesis that has been
considered as an antimitogenic factor in cell cycle regulation, playing
a crucial role in the maturation of the retina and the optic nerve
[21,22]. GPR143 is not involved in the production of melanin itself,
but rather the pigment distribution or production of a precursor like
L-DOPA as a cause of developmental anomalies of macular
development. The impaired macular development might then cause
the vision loss and nystagmus , as reported in this study.
The ocular disorders should be eliminated before the diagnosis of
congenital motor nystagmus can be made. However, some diseases
such as OA1 can be ignored or misdiagnosed. In general, OA1 is
characterized by presence of photophobia, congenital nystagmus,
strabismus, iris translucency, hypopigmentation of the ocular
fundus, foveal hypoplasia, and impaired vision . In
AfricanAmerican males, iris color is usually brown with little iris
translucency (compared to Caucasians where iris translucency is
more common) and individuals with darker skin may have scattered
hypopigmented macules, but this is rarely seen in the skin of
Caucasian individuals [24,25]. The characteristics of OA1 have not
been well defined in Asians. There were Chinese pedigrees of
congenital nystagmus reported showing that the patients in these
families had very similar symptoms as those in our pedigree. It is
interesting to reevaluate these pedigree to make sure the diagnosis of
congenital nystagmus, not ocular albinism, is correct, and the
impression that OA1 has rarely seen in China is correct.
In summary, this study adds a novel nonsense mutation to the
existing spectrum of GPR143 mutations in Chinese families with
X-linked OA1. The specific molecular mechanism by which these
GPR143 mutations result in OA1 is still unknown, further
functional studies are needed to provide new insights to this
inherited ocular disease.
The authors are deeply grateful to all the family members of this pedigree
for their cooperation in this study.
Copyright License Statement
All authors have contributed to the work, agreed with the presented
findings. The manuscript is not currently under consideration by any other
Conceived and designed the experiments: NY XYL. Performed the
experiments: YW XZ. Analyzed the data: XL CL. Contributed reagents/
materials/analysis tools: YY WY. Wrote the paper: SC.
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