Absent meibomian glands and cone dystrophy in ADULT syndrome: identification by whole exome sequencing of pathogenic variants in two causal genes TP63 and CNGB3.

BACKGROUND: Ectrodactyly is a rare congenital limb malformation characterized by a deep median cleft of the hand and/or foot due to the absence of central rays. It could be isolated or depicts a part of diverse syndromic forms. Heterozygous pathogenic variants in the TP63 gene are responsible for at least four rare syndromic human disorders associated with ectrodactyly. Among them, ADULT (Acro-Dermato-Ungual-Lacrimal-Tooth) syndrome is characterized by ectodermal dysplasia, excessive freckling, nail dysplasia, and lacrimal duct obstruction, in addition to ectrodactyly and/or syndactyly. Ophthalmic findings are very common in TP63-related disorders, consisting mainly of lacrimal duct hypoplasia. Absent meibomian glands have also been well documented in EEC3 (Ectrodactyly Ectodermal dysplasia Cleft lip/palate) syndrome but not in ADULT syndrome. METHODS: We report a case of syndromic ectrodactyly consistent with ADULT syndrome, with an additional ophthalmic manifestation of agenesis of meibomian glands. The proband, as well as her elder sister, presented with congenital cone dystrophy.The molecular investigation was performed in the proband using Whole Exome Sequencing. Family segregation of the identified variants was confirmed by Sanger sequencing. RESULTS: Two clinically relevant variants were found in the proband: the novel de novo heterozygous missense c.931A > G (p.Ser311Gly) in the TP63 gene classified as pathogenic, and the homozygous nonsense pathogenic c.1810C > T (p.Arg604Ter) in the CNGB3 gene. The same homozygous CNGB3 variation was also found in the sister, explaining the cone dystrophy in both cases. CONCLUSIONS: Whole Exome Sequencing allowed dual molecular diagnoses: de novo TP63-related syndromic ectrodactyly and familial CNGB3-related congenital cone dystrophy.

Turner syndrome: results of the first Tunisian study group on Turner syndrome (TuSGOT).

OBJECTIVES: Early diagnosis in Turner syndrome is desirable to optimize growth and puberty and yet, it is often made late. Here, we aim to identify age at diagnosis, clinical features at presentation and potential strategies to improve the care of TS girls. METHODS: Retrospective study, including patients from 14 care centers across Tunisia including neonatal and pediatric care units, adult endocrinology and genetics departments. RESULTS: We identified 175 patients with TS, karyotype showing 45, xmonosomy in 83(47.4 %) with mosaicism in 37(20 %). Mean ± SD, median (range) age at diagnosis available in 173 patients was 13 ± 9.2,12 (birth-48) years. The diagnosis was antenatal in 4(2.3 %), from birth-2 years in 14 (8 %)with lymphoedema (8)and dysmorphic features (9),2-12 years in 53 (35.5 %) including 35 with short stature, 13-18 years in 43(28.8 %) with short stature(28) and delayed puberty(14) and 35(23.5 %) after 18 years, related to ovarian insufficiency (20) and short stature (11). The associated malformations were cardiac in 14 (12.8 %), renal in 22 (19.6 %). A total of 56 girls (32 %) had proven gonadal dysgenesis and 13 (7 %) had otological problems. Parental height was available in 71 girls (40 %) of whom 59 were below the lower end of parental target range (LTR) (83 %). CONCLUSIONS: This first Tunisian multicenter study, the first African of its kind, reveals that more than half of Turner syndrome cases are diagnosed after the age of 12 years. Subsequently, national strategies for an earlier TS diagnosis are needed such as measuring and plotting parental heights as well as introducing a systematic height screening at 5 years in Tunisia with a view to carrying out a re-audit in five years' time.

A novel WFS1 variant associated with severe diabetic retinopathy in Wolfram syndrome type 1.

BACKGROUND: Wolfram syndrome type 1 is a rare neurodegenerative disorder including diabetes insipidus, diabetes mellitus, optic atrophy, and deafness, with variable additional findings. The phenotypic spectrum is very heterogeneous, with non-autoimmune juvenile-onset diabetes and optic atrophy as minimal criteria for the diagnosis. Biallelic mutations in the WFS1 gene are the causative genetic anomaly for the syndrome, with, however, no evident genotype-phenotype correlation. Among the clinical features of the disease, diabetic retinopathy depicts a rarely reported microvascular complication. In this report, we describe the clinical and genetic findings in a 26-year-old patient presenting with Wolfram syndrome and severe diabetic retinopathy. METHODS: The mutation screening was performed by polymerase chain reaction followed by Sanger sequencing of the entire coding sequence of the WFS1 gene. RESULTS: A novel homozygous missense variant c.1901A>T (p.Lys634Met) was found in the proband and classified as probably pathogenic according to the American College of Medical Genetics and Genomics. CONCLUSIONS: The molecular study of the WFS1 gene is essential for the diagnostic confirmation, to provide appropriate genetic counseling and a mutational screening in the at-risk relatives. The c.1901A>T (p.Lys634 Met) is a novel variant that could be responsible for a severe form of Wolfram syndrome with early and proliferative diabetic retinopathy.

Mucopolysaccharidosis type VII as a cause of recurrent Non-Immune Hydrops Fetalis: The first Tunisian case confirmed by Next-Generation Sequencing.

Non-Immune Hydrops Fetalis (NIHF) is an intrauterine condition characterized by excessive fluid accumulation in at least two fetal compartments in the absence of maternal circulating red cell antibodies. It is associated with a poor prognosis and a wide etiological spectrum. Among the metabolic causes, Mucopolysaccharidosis type VII depicts the most frequent type of lysosomal storage disorders in the cause of NIHF. Nonetheless, it remains an ultra-rare disorder, as less than 150 cases have been reported in the literature. This rarity seems to be related to misdiagnosis since the underlying etiology remains unelusive in most cases of NIHF. In this report, we describe the first Tunisian case of Mucopolysaccharidosis type VII caused by a homozygous mutation in the GUSB gene confirmed by a Next-Generation Sequencing gene panel in a patient with recurrent NIHF.

Mosaic parental germline mutations causing recurrent forms of malformations of cortical development.

To unravel missing genetic causes underlying monogenic disorders with recurrence in sibling, we explored the hypothesis of parental germline mosaic mutations in familial forms of malformation of cortical development (MCD). Interestingly, four families with parental germline variants, out of 18, were identified by whole-exome sequencing (WES), including a variant in a new candidate gene, syntaxin 7. In view of this high frequency, revision of diagnostic strategies and reoccurrence risk should be considered not only for the recurrent forms, but also for the sporadic cases of MCD.

Hexasomy of the Prader-Willi/Angelman critical region, including the OCA2 gene, in a patient with pigmentary dysplasia: case report.

Derivatives of chromosome 15, often referred to as inv dup(15), represent the most common supernumerary marker chromosome (SMC). SMC(15)s can be classified into two major groups according to their length: small SMC(15) and large ones. Depending on the amount of euchromatin, the carriers may either present with a normal phenotype or with a recognizable syndrome. Here we describe a patient with severe mental retardation, epilepsy, dysmorphic features and pigmentary dysplasia. His karyotype was 47,XY,+mar[41]/46,XY[9]. Chromosomal fluorescence in situ hybridization (FISH) showed the SMC to be originating from chromosome 15, dicentric and containing four copies of the Prader-Willi/Angelman Syndrome Critical Region (PWACR), including the OCA2 gene. Molecular studies indicated that it is maternally derived. This report supports the previous observations assuming that severity of phenotype in patients with SMC(15) depends on the dosage of the PWACR and that skin pigmentation is correlated to OCA2 gene copy number.

A novel frame shift mutation in the PQBP1 gene identified in a Tunisian family with X-linked mental retardation.

Mental retardation (MR) is the most frequent cause of serious handicap in children and young adults. Despite recent progress, in most cases the molecular defects underlying this disorder remain unknown. Linkage studies followed by mutational analysis of known X-chromosomal genes related to mental retardation (MRX genes) localized within defined genetic intervals represent a rational strategy to identify a genetic cause of the disorder. Here, we report a Tunisian family including 3 males with severe to mild mental retardation, short stature, lean body and microcephaly; we mapped the disease to a unique interval encompassing Xp21.1-Xq21.33 (with a maximum LOD score of 0.90). Subsequent mutation analysis of genes located in this interval allowed us to identify a truncating mutation in the PQBP1 gene. This mutation is an insertion of an adenosine residue in exon 5 (c.631insA). This frameshift insertion causes premature stop codon at amino acid position 226. The observed mutation was found in all males with MR in this family. Together with previously reported observations, our data further confirm that PQBP1 gene should be tested for males showing mental retardation, short stature, lean body and microcephaly.

Marfan syndrome in a Triple-X girl: a new association?

BACKGROUND: Triple X is a sex chromosomal abnormality that involves the presence of three sex chromosomes resulting in 47, XXX karyotype. Most patients suffering from this syndrome are usually mentally normal or subnormal with no gross malformation. AIM: to report an unusual association between Triple X and Marfan disease in a girl. CASE REPORT: A case of a triple X girl with craniofacial dysmorphy and skeletal anomalies, who did feat Marfan criteria by age, is presented. CONCLUSION: To the best of our knowledge this association has never been reported. Some clinical features are common between Triple X and Marfan disease so a careful follow-up is needed and investigations should be performed in these patients because Marfan syndrome may be incomplete in early age.

X linked mental retardation.

BACKGROUND: Mental retardation (MR) is a group of heterogeneous clinical conditions. There are more than 900 genetic disorders associated with MR and it affects around 3% of the general population. Many MR conditions described are syndromic, fragile X syndrome being the most common clinical entity among them. X linked mental retardation (XLMR) is subdivided in two categories: syndromic XLMR (MRXS) when MR is associated with clinical features and non-syndromic XLMR (MRX) when MR is isolated. AIM: The aim of this systematic review of the literature was to join together the results of several studies related to X linked mental retardation and to present various genes implicated in this disease. In this review, focus has been given on genes implicated in mental retardation, the clinical data and on phenotype-genotype correlations. METHODS: An exhaustive electronic and library research of the recent literature was carried out on the Web sites "Science Direct" and "Interscience Wiley". The key words used were "mental retardation", "X chromosome", "gene", "syndromic mental retardation", "non-syndromic mental retardation". RESULTS: In this review a number of X linked genes, the clinical features associated with the gene abnormality, and the prevalence of the disease gene are discussed. We classified these genes by order of their first implication in MR. A table presented on the XLMR Update Web site who list the 82 known XLMR genes is available as XLMR Genes and corresponding proteins.

MLPA subtelomere analysis in Tunisian mentally retarded patients.

Subtelomeric rearrangements significantly contribute to idiopathic mental retardation and result in several mental retardation syndromes; however, most subtelomeric defects lack a characteristic phenotype. Thirty patients with unexplained mental retardation, a normal R banded karyotype at the 550 band, and no clinically recognizable syndrome were screened by Multiplex ligation-dependent probe amplification (MLPA). Four anomalies were identified: deletion 17q, duplications (4q), and associated duplications 15q and Xq. This duplication was found in two sisters of the proband. Anomalies were unidentified by the conventional technique. The prevalence of subtelomeric imbalances in our cohort of moderate to severe mental retardation is around 13% and is consistent with the literature. The sensitivity of the MLPA technique was characterized on cytogenetically verified positive and negative controls. MLPA is a fast, reliable, and relatively inexpensive technique to detect subtelomeric rearrangement in comparison with the fluorescence in situ hybridization (FISH) technique.

A 24-Mb deletion in 14q in a girl with corpus callosum hypoplasia.

Interstitial deletions of 14q including band 14q31 are uncommon. We report on a 3 year-old Tunisian girl who had a de novo interstitial deletion of the long arm of chromosome 14. The molecular cytogenetic study has identified the deletion as a del(14)(q24.3q32.2) covering nearly 24Mb. This abnormality was associated to phenotypic manifestations, mainly peculiar face, developmental delay and hypoplastic corpus callosum.

A novel splice mutation in PAK3 gene underlying mental retardation with neuropsychiatric features.

PAK3-related mental retardation represents a rare cause of X-linked mental retardation associated with behavioural symptoms. So far, four families carrying PAK3 mutations have been reported, and in most cases PAK3 dysfunction resulted from missense mutations thought to affect either the catalytic or the N-terminal regulatory domain activity. Here, we report on a Tunisian family of X-linked moderate mental retardation with behavioural symptoms, common dysmorphic features, oro-motor impairment and secondary microcephaly. Linkage analysis showed that affected male subjects and obligate carrier female subjects share a common haplotype in the Xp21.31 - Xq23 region that contains the PAK3 gene. Direct sequencing of PAK3 coding exons and flanking intronic sequences allowed us to identify the first splice mutation in PAK3 gene located at the 5' end of intron 6 (c.276+4A>G), which results in a complete switch-off of the genuine donor splice site and an activation of a cryptic donor splice site (GTAAG) located four nucleotides downstream to the genuine one. RT-PCR experiments using the RNA from the patient's lymphoblasts showed that PAK3 transcripts contain four additional nucleotides that lead to a disruption of reading frame with a premature stop codon at position 128. Together with previously reported observations, our data further confirm that PAK3 mutations result in a specific form of X-linked mental retardation with fairly constant clinical features.

The creatine transporter gene paralogous at 16p11.2 is expressed in human brain.

Autism is a complex neurodevelopmental disorder characterized by impairment of social interaction, language, communication, and stereotyped, repetitive behavior. Genetic predisposition to autism has been demonstrated in families and twin studies. About 5-10% of autism cases are associated with chromosomal abnormalities or monogenic disorders. The identification of genes involved in the origin of autism is expected to increase our understanding of the pathogenesis. We report on the clinical, cytogenetic, and molecular findings in a boy with autism carrying a de novo translocation t(7;16)(p22.1;p11.2). The chromosome 16 breakpoint disrupts the paralogous SLC6A8 gene also called SLC6A10 or CT2. Predicted translation of exons and RT-PCR analysis reveal specific expression of the creatine transporter paralogous in testis and brain. Several studies reported on the role of X-linked creatine transporter mutations in individuals with mental retardation, with or without autism. The existence of disruption in SLC6A8 paralogous gene associated with idiopathic autism suggests that this gene may be involved in the autistic phenotype in our patient.

De novo balanced translocation t (7;16) (p22.1; p11.2) associated with autistic disorder.

The high incidence of de novo chromosomal aberrations in a population of persons with autism suggests a causal relationship between certain chromosomal aberrations and the occurrence of isolated idiopathic autism. We report on the clinical and cytogenetic findings in a male patient with autism, no physical abnormalities and a de novo balanced (7;16)(p22.1;p16.2) translocation. G-banded chromosomes and fluorescent in situ hybridization (FISH) were used to examine the patient's karyotype as well as his parents'. FISH with specific RP11-BAC clones mapping near 7p22.1 and 16p11.2 was used to refine the location of the breakpoints. This is, in the best of our knowledge, the first report of an individual with autism and this specific chromosomal aberration.

[Interest of studying subtelomeric abnormalities by in situ fluorescent hybridization to explore idiopathic mental retardation]. / Intérêts de l'étude des remaniements subtélomériques par la technique d'hybridation fluorescente (FISH) dans l'exploration des retards mentaux idiopathiques.

Nowadays, the genetic basis of mental retardation is a huge field of investigations. Genetic abnormalities frequently give rise to a mental retardation phenotype and are observed in 10 to 40% of known etiologies. New syndromes have identified (chromosome 1p, 22q, 3q29 and 9q34) but for 60% of patients there is no etiology because there is no characteristic phenotype. Many studies involve subtelomeric duplications and deletions in idiopathic mental retardation. The autours describe and discuss the interest and the limits of telomeric FISH [Chromoprobe Multiprobe T System] in exploring mental retardation.

[Molecular diagnosis of fragile X syndrome]. / Diagnostic moleculaire du sydrome de l'X fragile.

BACKGROUND: The fragile X syndrome was the most frequent etiology of hereditary mental retardation but the clinical diagnosis is not easy and the individual clinical symptoms were not specific so the confirmation will be made par molecular study of the gene of the fragile X syndrome. The aim of our study is to realise the molecular diagnosis of the fragile X syndrome in 200 Tunisian boys with mental retardation. Our results shows that the frequency of the fragile X syndrome is 7,6%. In the most cases there is a family history of mental retardation with medium age at 11 years. All the boys with the full mutation have mental retardation, dysmorphic features and macro-orchidism (pubescent boy) CONCLUSION: The screening of the molecular abnormalities of FMRI gene must be realised in every boy with mental retardation or boy with delayed speech without any identified etiology. The earlier diagnosis is important for genetic counselling.

MEFV mutations in Tunisian patients suffering from familial Mediterranean fever.

OBJECTIVES: To identify the frequency and distribution of familial Mediterranean fever (FMF) gene (MEFV) mutations in Tunisian patients. PATIENTS AND METHODS: This study was performed in the Genetic Department of Tunis University Hospital. A clinical diagnosis of FMF was made according to published criteria. Mutation screening of the MEFV gene was performed in the Human Genetic Laboratory of the "Faculté de Medecine de Tunis" for 8 mutations including the 5 most common known mutations M694V, V726A, M694l, M680l, and E148Q. The tests performed were polymerase chain reaction (PCR) restriction-digestion for M694V, V726A, M680l, R761H, E148Q; amplification refractory mutation system for A744S, M694l; and PCR-electrophoresis assay for l692del. RESULTS: Of the 139 unrelated patients investigated, 61 (44%) had 1 or 2 mutations. In 78 (56%) probands no mutation was identified: 28 patients were homozygous; 16 were compound-heterozygous; 2 had complex alleles; and 17 had only 1 identifiable mutation. Of the mutations, M680l, M694V, M694l, V726A, A744S, R761H, l692DEL, and E148Q accounted for 32, 27, 13, 5, 3, 1, 1, and 18%, respectively. CONCLUSION: The profile of the MEFV gene mutations in the Tunisian population is concordant with other Arab populations but with some differences. M680l is the most common mutation, while V726A, the commonest mutation among Arabs, is rare in our population.

[Treacher-Collins syndrome: clinical and genetic aspects apropos of 4 cases of which 1 is familial]. / Le syndrome de Treacher Collins: aspects clinique et génétique à propos de 4 observations dont une familiale.

Treacher Collins syndrome was first mentioned by Thompson in 1847, and described by Treacher Collins in 1900, then it was called mandibulo-facial dysostosis and well defined by Franceschetti in 1949. It is a very rare affection occurring lin 50.000 live births, which includes facial and auricular anomalies leading to functional, morphological and psychological difficulties due to related handicaps. Treacher Collins syndrome is inherited as autosomal dominant pattern with a variable expressivity and incomplete penetrance of "TCOF1" gene localized at 5q31.3q32. Today the gene is well identified and several mutations have been reported. In this paper we report the case of 4 Tunisian unrelated girls with Treacher Collins syndrome. One of them was born from an affected father. Clinical diagnostic was performed between age 12 days and 2 years demonstrating the large dysmorphic expression. Main clinical features were present in all reported cases. Family at risk might have genetic counselling and probably prenatal diagnostic in some situations. Out of our observations, we gave genetic counselling and proposed ultrasound prenatal diagnosis for two families without molecular study.

Molecular analysis of the SMN1 and NAIP genes in 60 Tunisian spinal muscular atrophy patients.

In this study we examined the deletion of SMN and NAIP genes in 60 Tunisian families. There were 35 patients with type I SMA. 18 with type II SMA. 6 with type III SMA and I with type IV SMA. The age of onset was before 6 months for type I, between 6 months and 2 years for type II, between 2 years and 17 years for type III and 30 years for type IV. Exon 7 of SMNI gene was homozygously deleted in 95% (57/60) of SMA patients. There was a higher frequency of homozygous absence of SMN1 in type I and type II (100% and 94% respectively) than in type III (66,7%). SMN1 exon 8 was undetectable in 88% (53/60) of patients. The case type II patient with homozygous deletion of SMNI exon 7 and not exon 8 was tested for the presence of a hybrid SMN gene. This patient showed in the second PCR a SMN1 exon 8 product by restriction site assay indicating that a gene conversion event had occurred. All parents' individuals retained one copy of their SMN1 gene. Exon 5 of NAIP gene was homozygously deleted in 58% (35/60) of patients (77% in type I (27/35), 27,7% in type II (5/18), 50% (3/6) in type III. No patient had a deletion in NAIP gene without a deletion in the SMN1 gene. Homozygous deletion of NAIP exon 5 was detected in 1 parent. Our results show that the incidence of NAIP deletion is higher in the more severe SMA cases.