Genetic investigation of XPA gene: high frequency of the c.682C>T mutation in Moroccan XP patients with moderate clinical profile
Kindil et al. BMC Res Notes
Genetic investigation of XPA gene: high frequency of the c.682C>T mutation in Moroccan XP patients with moderate clinical profile
Zineb Kindil 0 2
Mohamed Amine Senhaji 0
Amina Bakhchane 0
Hicham Charoute 0
Soumia Chihab 1
Sellama Nadifi 2
Abdelhamid Barakat 0
0 Human Molecular Genetics Laboratory, Institut Pasteur du Maroc , 1, Place Louis Pasteur, 20360 Casablanca , Morocco
1 Department of Dermatology, Hospital University Ibn Rochd , Casablanca , Morocco
2 Laboratory of Genetics and Molecular Pathology, Faculty of Medicine, Hassan II University , Casablanca
Objective: Xeroderma pigmentosum (XP) is a genetically and clinically heterogeneous disease, associated with an inherited defect in one of eight different genes (XPA to XPG and XPV). In addition to the early onset of the skin manifestations, the XP group A is marked by the presence of a mild to severe neural disorders which appear tardily and worsens with age. In this study, 9 patients with moderate clinical profile belonging to 6 XP families were recruited to determine the XPA mutational spectrum in Morocco, using the direct sequencing of the whole coding region of the XPA gene. Results: The genetic investigation of the XPA gene showed that 7 from 9 patients were homozygous for the c.682C>T, p.Arg228X mutation, while all their investigated family members were heterozygous. The frequency of this mutation was estimated to be 83.33% (5/6 families) .The molecular analysis of the 5 other exons of the XPA gene, showed that the 2 negative siblings carried no mutation in the XPA gene. This finding suggests that c.682C>T (p.Arg228X) mutation is relatively associated with moderate phenotype in XP group A Moroccan families; this result will also contribute to improve the molecular diagnosis of XP disease in Moroccan patients.
Xeroderma pigmentosum; XPA; Mutation; Morocco
Xeroderma pigmentosum (XP) is a rare disease
inherited under the autosomal recessive mode. It is clinically
characterized by sunlight hypersensitivity, pigmentary
changes, premature skin ageing, malignant skin and
eyes tumor development [
]. This genodermatosis is
responsible evenly for a markedly elevated risk of
developing other skin and ocular disorders with or without
neurological abnormalities [
pigmentosum disease shows also a high genetic heterogeneity, it
has been classified into eight complementation groups
(XPA to XPG and XPV) [
]. The XPC, XPD and XPA
complementation groups present the most frequent
forms of Xeroderma pigmentosum in Europe, North
Africa, Japan and the USA, as they are responsible for
about 90% of XP patients worldwide [
]. In Japan about
60% of XP patients belong to group A, moreover, nearly
1% of Japanese population shares the (c.390-1G>C) XPA
gene mutation with a founder effect [
]. The XPA human
gene ensures a key role in verification of protein
damage during the NER, this gene is composed of 6 exons
and encodes a 273 amino acid protein which is involved
in DNA excision repair pathway [
]. The XPA is a highly
mutated gene, and about 32 mutations with different
degree of severity have been identified [according to the
Human Gene Mutation Database (HGMD): http://www.
hgmd.cf.ac.uk/ac/index.php] (Table 1). This explains
the fact that the XP group A patients present high
heterogeneity of cutaneous and ocular symptoms, which
are qualified as moderates comparing with the XPC
group, who is known as the most severe form of
Xeroderma Pigmentosum. Unlike the XP group C phenotype,
XP group A patients present also neurological
abnormalities that appeared tardily and independently from
UVinduced DNA lesions [
In Morocco, prevalence of the xeroderma
pigmentosum is approximately 1/80 504, which is higher than
that found in Europe and the USA [
]. Soufir et al. have
reported that XPC gene is the major cause of xeroderma
pigmentosum in North Africa, this study showed also
that the founder mutation 1643-1644delTG in XPC gene
is responsible for a high proportion of XP cases [
This founder mutation was estimated to be responsible
of more than 76% XP in Moroccan patients [
]. To the
best of our knowledge, there is no study investigating the
spectrum of XPA gene mutations in the Moroccan
population. Thus, 9 Moroccan patients suspected to be XP
group A were analyzed; they present different degrees of
severity of neuronal disorders and their age range from 7
to 33. This work aims to describe the mutation spectrum
of the XPA gene in Moroccan XP patients, and clarify
its involvement in molecular diagnosis of XP group A
We recruited 9 XPA patients (5 male and 4 female
individuals), belonging to 6 unrelated families to describe the
genetic profile of XPA diseases in Moroccan XP patients.
The Classification of these patients as XP group A was
based on clinical symptoms observed in almost the
totality of them, including an abnormal neurological
development, which worsens with age and moderate skin lesions
which start earlier than neurological signs. One of our
patients, a 7 years child (XP43.01) whose recruitment
was based in his family history, shows no neurological
disorders. Our participants all originated from different
regions of Morocco and are all diagnosed and treated at
the department of Dermatology in Ibn Rochd University
Hospital in Casablanca.
A detailed questionnaire giving all information
regarding the clinical data of each patient was filled in. An
informed consent was obtained from patients as well as
their relatives and was approved by the local committee
on research ethics of the Pasteur Institute in Morocco.
For all patients and their relatives, the DNA extraction
from whole blood was carrying out according to phenol
chloroform standard protocol [
]. To disclose the
presence of genetic variations in our patients, the six exons of
XPA gene were amplified using specific primers (Table 2).
The PCRs were done in particular conditions included
initial denaturation at 95 °C for 5 min, 35 cycles of
denaturation at 94 °C for 30 s, annealing at a specific
temperature which change depending of the primer couple for
35 s, extension at 72 °C for 40 s, and final elongation at
72 °C for 7 min.
PCRs were performed in 15 µl final mixture volume
containing 30–50 ng of DNA, 6 pmol of each primer,
a The first fragment of exon 6
b The second fragment of exon 6
200 µM of dNTPs, 3 mM of MgCl2, 1× PCR buffer,
0.75 U of GoTaq polymerase (Promega, Madison, USA).
Purified PCR product was sequenced using the BigDye
Terminator v 1.1 Standard Kit according to the
manufacturer’s recommendations (Applied Biosystems, Foster
City, CA, USA) using ABI 3130 Genetic Analyzer.
This study involved 6 unrelated XPA Moroccans families,
including 9 patients. All patients developed pokilodermia
as first symptom of XP at a mean age of 36 month, this
pokilodermia was present in all patients’ sun exposed
zones (face and hand), and was more marked in patients
with low sun protection, 44.44% (4/9) of our patients
showed telangiectasia, and only one woman suffered
from malignant tumors, she developed an non
melanoma skin cancer (NMSC) at 16 years old, the
Pathological analysis demonstrated an 5 × 7.5 × 3 mm basal
cell carcinoma (BCC) located in the left side of the base
of her nose, a later dermatoscopy examination
demonstrated that she has also developed two benign tumors at
20 and 23 years old. No ocular malignancies were noticed
in our patients. However five patients had
photophobia and three showed keratitis in one or both eyes, one
patient XP22.02 had a repetitive eye inflammation which
was first diagnosed at the age of 10 years old. All our
recruited patients was born with normal size and weight,
an neurological abnormalities progression was shown
in 8 among them; including a low sensorineural
hearing loss observed in two siblings XP16.01 and XP16.02,
a 33 years woman XP39.01 showed a severe mental and
psychomotor retardation which progress in a loss of
ability to walk, speech and motion disorders; according to
her family history, two of her sisters had a typical XPA
clinical profile, they also developed an progressive
intellectual impairment and died in their early adulthood.
Those patient’s sisters hadn’t been sequenced for the XPA
gene, but their medical history mentioned that during
their lives they developed all clinical signs
characteristic of the Xeroderma pigmentosum type A. One young
boy XP43.01 had a normal neurological development at
the moment of his recruitment (Table 3), his family
history indicate that two members of his maternal family
(aunt and uncle), had a XPA clinical profile, similarly to
the XP39.01 sister’s, they developed a severe
neurological troubles in their adulthood, before dying from cancer
at the age of 29 and 34 years old respectively. The other
patients aged between 12 and 18 years old had no similar
antecedents in their families.
The screening of the coding region of the XPA gene
disclosed the presence in homozygote state of the recurrent
mutation c.682C>T (p.Arg228Ter) in 7/9 XP patients.
This punctual variation localized in the exon 6 of the XPA
gene leads to a premature termination of the encoded
protein. Furthermore, all tested parents and healthy
relatives of these patients were heterozygous for this
mutation (Fig. 1). Additional investigation showed that 2
female siblings had no mutations in the whole XPA gene;
even so they present a moderate clinical profile with mild
neural retardation, this clinical feature is maybe related
with molecular variations in other XP gene (XPB, XPD or
Xeroderma pigmentosum is genetically and clinically
heterogonous disease, its incidence was estimated at
1/1,000,000 in the United States and Europe, 1/20,000–
100,000 in Japan [
], and around 1/10,000–50,000 in
North Africa and the Middle East [
]. Eight genes
were identified as implicated in this rare
genodermatosis among them the XPA gene [
], which is characterized
by neurological defects [
]. In Morocco, no data
concerning the XP group A incidence is available. However
in this study a clinical and mutational investigation of
XPA complementation group is performed in Moroccan
patients, in order to contribute to improve diagnosis for
XP group A patients and to establish a genetic counseling
for their families.
The majority of our patients 88.88% (8/9) were born
from consanguineous parents; they are aged between
7 and 33 years with average age of 16.42 years.
Moreover, almost all of them showed moderate skin and ocular
symptoms. Neurological disorders were also observed
especially in aged patients. The patient XP43.01 too
young to show a mental abnormal development had a
normal neurological profile.
The XPA is one of six XP protein factors overriding
in human NER machinery [
]. Nowadays, over thirty
mutations affecting the XPA gene had been listed at the
Human Gene Mutation Database; the majority of them
are Missense variations (http://www.hgmd.cf.ac.uk/ac/
index.php). The direct sequencing of the exon 6 of XPA
gene showed that about 83% of screened families bear
the c.682C>T (p.Arg228X) point mutation, this
mutation correspond to C to T transition at position 682 of
the coding DNA, and leads to a truncated protein. This
nonsense mutation occurs in the C-terminal domain of
XPA protein, and this could explain the moderate clinical
manifestations of our XP group A patients; since the
severity of the clinical phenotype is observed when
mutations are located in the DNA binding region (aa 98–219)
(Fig. 2). This moderate phenotype was also detected
in American, European and Japanese families who are
sharing this punctual mutation [
]. In Tunisia, six out
of seven XP group A patients had this nonsense
mutation with a frequency of 86% [
]. In addition, a previous
study has shown that all XP group A Tunisian patients
with moderate phenotype had this mutation with
founder effect [
]. The same mutation was also
identified in Algerian XP group A patients [
]. A study leading
by Soufir et al. including 66 unrelated XP families from
North Africa, showed that the c.682C>T (p.Arg228X)
mutation was present in all XP group A analyzed patients
with a frequency of 12% [
]. This suggested that this
mutation may have a common founder effect in the
North African region.
Severe clinical phenotype is usually observed when
patients had mutations within exons 3–5, as reported in
four Egyptians [
] and one Iranian patient [
]. A very
severe abnormalities were also observed in a Japanese
patient who present a mutation located at intron 3 in the
splice site [
On the other hand, the molecular investigation in
patients with no mutation in exon 6, has demonstrated
that those two young siblings don’t share any molecular
variation in the others XPA gene exons. As perspective,
those two patients will be analyzed for the XPB, XPD and
XPF genes responsible of rare forms of xeroderma
pigmentosum with neurological disorders [
In conclusion, our finding suggested that the c.682C>T
(p.Arg228X) mutation is relatively associated with
moderate clinical profile in XP group A Moroccan patients.
This work in which the XPA gene were analyzed for the
first time in the Moroccan population will provide a basis
for the prenatal diagnosis and genetic counseling.
However, the sample size is relatively small and further
studies are necessary to determine the spectrum of XPA gene
mutations is Moroccan patients.
BCC: basal cell carcinoma; NER: nucleotide excision repair; NMSC: melanoma
skin cancer; PCR: polymerase chain reaction; XP: xeroderma pigmentosum;
XPA: xeroderma pigmentosum, complementation group A; XPC: xeroderma
pigmentosum, complementation group C; XPD: xeroderma pigmentosum
complementary group D; XPG: xeroderma pigmentosum complementary
group G; XPV: xeroderma pigmentosum, variant type.
AB conceived, designed and coordinated the study. ZK performed the
laboratory work. MAS helped in the laboratory work. ZK wrote the paper. AmB,
HC, SC and SN participated in interpretation of results. All authors read and
approved the final manuscript.
The authors would like to express their deep gratitude to patients and their
families, as well as the dermatology service members for their contribution to
The authors declare that they have no competing interests.
Availability of data and supporting materials
Please contact Dr. Abdelhamid Barakat () for data
Consent for publication
Ethics approval and consent to participate
All participants signed informed consent forms. In the case of children aged
less than 16 years old, we obtained parental consent. The study protocol
was approved by local Committee on Research Ethics of Pasteur Institut of
This work was supported by Institut Pasteur du Maroc.
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
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