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Unlabelled: We aimed to identify causal mutation(s) in 13 patients with thyroid dyshormonogenesis (TD) from three consanguineous Tunisian families. A 12-year clinical follow-up showed phenotypic variability ranging from the presence to the absence of goiter, sensorineural deafness, and mental retardation. Genetic analysis using microsatellite markers within two candidate genes (TPO and PDS) gave evidence of linkage with the TPO gene. Sequencing of its 17 exons and their flanking intron-exon junctions revealed the previously described c.875C>T (p.S292F) mutation in homozygous state. No additional mutations were found in either a 900 bp of the TPO gene promoter or PDS gene. In silico analysis showed that p.S292F mutation might reduce the catalytic cavity of the TPO which would restrict access of a potential substrate to the catalytic pocket. Using 4SNPs and one microsatellite marker in the TPO gene, an associated haplotype: G-C-G-G-214 was found, giving evidence of a founder mutation.Conclusion: This is the first description of a TD causing mutation in Tunisia and thus may help to develop a genetic screening protocol for congenital hypothyroidism in the studied region. Although structural modeling suggested a pathogenic effect of this mutation, functional studies are needed. Additional causing and/or modifier genes, together with late diagnosis could explain the clinical variability observed in our patients. [ABSTRACT FROM AUTHOR]

Angle-closure glaucoma (ACG) is a subset of glaucoma affecting 16 million people. Although 4 million people are bilaterally blind from ACG, the causative molecular mechanisms of ACG remain to be defined. High intraocular pressure induces glaucoma in ACG. High intraocular pressure traditionally was suggested to result from the iris blocking or closing the angle of the eye, thereby limiting aqueous humor drainage. Eyes from individuals with ACG often have a modestly decreased axial length, shallow anterior chamber and relatively large lens, features that predispose to angle closure. Here we show that genetic alteration of a previously unidentified serine protease (PRSS56) alters axial length and causes a mouse phenotype resembling ACG. Mutations affecting this protease also cause a severe decrease of axial length in individuals with posterior microphthalmia. Together, these data suggest that alterations of this serine protease may contribute to a spectrum of human ocular conditions including reduced ocular size and ACG. [ABSTRACT FROM AUTHOR]

Deleterious mutations of SLC26A4 cause Pendred syndrome (PS), an autosomal recessive disorder comprising goitre and deafness with enlarged vestibular aqueducts (EVA), and nonsyndromic hearing loss (NSHL). However, the SLC26A4 hyperactivity was recently associated with the emergence of autoimmune thyroid diseases (AITD) and asthma among human and mouse model. Here, by direct sequencing, we investigate the sequences of the 20 coding exons (2 to 21) of SLC26A4 and their flanking intron-exon junctions among patients affected with Graves' disease (GD) hyperthyroidism. Ten mono-allelic variants were identified, seven of which are intronic and previously unreported. Two, c.898A>C (p.I300L) and c.1061T>C (p.F354S), of the three exonic variants are non synonymous. The p.F354S variant is already described to be involved in PS or NSHL inheritances. The exploration by PCR-RFLP of p.I300L and p.F354S variants among 132 GD patients, 105 Hashimoto thyroiditis (HT), 206 Healthy subjects and 102 families with NSHL have shown the presence of both variants. The p.F354S variation was identified both among patients (1~HT and 3 GD) and healthy subjects (n=5). Whereas, the p.I300L variant was identified only in GD patients (n=3). Our studies provide evidence of the importance of systematic analysis of SLC26A4 gene sequences on models other than deafness. This approach allows the identification of new variants and the review of the pathogenic effects of certain mono-allelic variants reported responsible for PS and NSHL development. [ABSTRACT FROM AUTHOR]

Autosomal recessive retinitis pigmentosa (ARRP) is a genetically heterogeneous disorder. ARRP could be associated with extraocular manifestations that define specific syndromes such as Usher syndrome (USH) characterized by retinal degeneration and congenital hearing loss (HL). The USH type II (USH2) associates RP and mild-to-moderate HL with preserved vestibular function. At least three genes USH2A, the very large G-protein-coupled receptor, GPR98, and DFNB31 are responsible for USH2 syndrome. Here, we report on the segregation of non-syndromic ARRP and USH2 syndrome in a consanguineous Tunisian family, which was previously used to define USH2B locus. With regard to the co-occurrence of these two different pathologies, clinical and genetic reanalysis of the extended family showed (i) phenotypic heterogeneity within USH2 patients and (ii) excluded linkage to USH2B locus. Indeed, linkage analysis disclosed the cosegregation of the USH2 phenotype with the USH2C locus markers, D5S428 and D5S618, whereas the ARRP perfectly segregates with PDE6B flanking markers D4S3360 and D4S2930. Molecular analysis revealed two new missense mutations, p.Y6044C and p.W807R, occurring in GPR98 and PDE6B genes, respectively. In conclusion, our results show that the USH2B locus at chromosome 3p23–24.2 does not exist, and we therefore withdraw this locus designation. The combination of molecular findings for GPR98 and PDE6B genes enable us to explain the phenotypic heterogeneity and particularly the severe ocular affection first observed in one USH2 patient. This report presents an illustration of how consanguinity could increase familial clustering of multiple hereditary diseases within the same family.European Journal of Human Genetics (2009) 17, 474–482; doi:10.1038/ejhg.2008.167; published online 15 October 2008 [ABSTRACT FROM AUTHOR]

Hereditary nonsyndromic hearing impairment (HI) is extremely heterogeneous. Mutations of the transmembrane channel-like gene 1 (TMC1) have been shown to cause autosomal dominant and recessive forms of nonsyndromic HI linked to the loci DFNA36 and DFNB7/B11, respectively. TMC1 is 1 member of a family of 8 genes encoding transmembrane proteins. In the mouse, MmTmc1 and MmTmc2 are both members of Tmc subfamily A and are highly and almost exclusively expressed in the cochlea. The restricted expression of Tmc2 in the cochlea and its close phylogenetic relationship to Tmc1 makes it a candidate gene for nonsyndromic HI. We analyzed 3 microsatellite markers linked to the TMC1 and TMC2 genes in 85 Tunisian families with autosomal recessive nonsyndromic HI and without mutations in the protein-coding region of the GJB2 gene. Autozygosity by descent analysis of 2 markers bordering the TMC2 gene allowed us to rule out its association with deafness within these families. However, 5 families were found to segregate deafness with 3 different alleles of marker D9S1837, located within the first intron of the TMC1 gene. By DNA sequencing of coding exons of TMC1 in affected individuals, we identified 3 homozygous mutations, c.100C→T (p.R34X), c.1165C→T (p.R389X) and the novel mutation c.1764G→A (p.W588X). We additionally tested 60 unrelated deaf Tunisian individuals for the c.100C→T mutation. We detected this mutation in a homozygous state in 2 cases. This study confirms that mutations in the TMC1 gene may be a common cause for autosomal recessive nonsyndromic HI. Copyright © 2008 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

The congenital muscular dystrophies (CMD) constitute a clinically and genetically heterogeneous group of autosomal recessive myopathies. Patients show congenital hypotonia, muscle weakness, and dystrophic changes on muscle biopsy. Mutations in four genes (FKT1, POMGnT1, POMT1, FKRP) encoding putative glycosyltransferases have been identified in a subset of patients characterized by a deficient glycosylation of α-dystroglycan on muscle biopsy. FKRP mutations account for a broad spectrum of patients with muscular dystrophy, from a severe congenital form with or without mental retardation (MDC1C) to a much milder limb-girdle muscular dystrophy (LGMD2I). We identified two novel homozygous missense FKRP mutations, one, A455D, in six unrelated Tunisian patients and the other, V405L, in an Algerian boy. The patients, between the ages of 3 and 12 years, presented with a severe form of MDC1C with calf hypertrophy and high serum creatine kinase levels. None had ever walked. Two had cardiac dysfunction and one strabismus. They all had mental retardation, microcephaly, cerebellar cysts, and hypoplasia of the vermis. White matter abnormalities were found in five, mostly when cranial magnetic resonance imaging was performed at a young age. These abnormalities were shown to regress in one patient, as has been observed in patients with Fukuyama CMD. Identification of a new microsatellite close to the FKRP gene allowed us to confirm the founder origin of the Tunisian mutation. These results strongly suggest that particular FKRP mutations in the homozygous state induce structural and clinical neurological lesions in addition to muscular dystrophy. They also relate MDC1C to other CMD with abnormal protein glycosylation and disordered brain function. [ABSTRACT FROM AUTHOR]

Fanconi anemia (FA) is a rare autosomal recessive disease characterized by progressive pancytopenia, congenital malformations, and predisposition to acute myeloid leukemia. Fanconi anemia is genetically heterogeneous, with at least eight distinct complementation groups of FA (A, B, C, D1, D2, E, F, and G) having been defined by somatic cell fusion studies. Six genes (FANCA, FANCC, FANCD2, FANCE, FANCG, and FANCF) have been cloned. Mutations of the seventh Fanconi anemia gene, BRCA2, have been shown to lead to FAD1 and probably FAB groups. In order to characterize the molecular defects underlying FA in Tunisia, 39 families were genotyped with microsatellite markers linked to known FA gene. Haplotype analysis and homozygosity mapping assigned 43 patients belonging to 34 families to the FAA group, whereas one family was probably not linked to the FANCA gene or to any known FA genes. For patients belonging to the FAA group, screening for mutations revealed four novel mutations: two small homozygous deletions 1693delT and 1751-1754del, which occurred in exon 17 and exon 19, respectively, and two transitions, viz., 513G → A in exon 5 and A → G at position 166 (IV-S24+166A → G) of intron 24. Two new polymorphisms were also identified in intron 24 (IVS24-5G/A and IVS24-6C/G). [ABSTRACT FROM AUTHOR]

A correction to the article "Segregation of S292F TPO gene mutation in three large Tunisian families with thyroid dyshormonogenesis: evidence of a founder effect" that was published in the November 14, 2015 issue is presented.

Congenital microphthalmia (CMIC) is a common developmental ocular disorder characterized by a small, and sometimes malformed, eye. Posterior microphthalmia (PM) and nanophthalmia are two rare subtypes of isolated CMIC characterized by extreme hyperopia due to short axial length and elevated lens/eye volume ratio. While nanophthalmia is associated with a reduced size in both anterior and posterior segments, PM involves a normal-size anterior chamber but a small posterior segment. Several genes encoding transcription and non-transcription regulators have been identified in different forms of CMIC. MFRP gene mutations have, for instance, been associated with nanophthalmia, and mutations in the recently identified PRSS56 gene have been linked to PM. So far, these two forms of CMIC have been associated with 9 mutations in PRSS56. Of particular interest, a c.1059_1066insC mutation has recently been reported in four Tunisian families with isolated PM and one Tunisian family with nanophthalmia. Here, we performed a genome-wide scan using a high density single nucleotide polymorphism (SNP) array 50 K in a large consanguineous Tunisian family (PM7) affected with PM and identified the same causative disease mutation. A total of 24 polymorphic markers spanning the PRSS56 gene in 6 families originating from different regions of Tunisia were analyzed to investigate the origin of the c.1059_1066insC mutation and to determine whether it arose in a common ancestor. A highly significant disease-associated haplotype, spanning across the 146kb of the 2q37.1 chromosome, was conserved in those families, suggesting that c.1059_1066insC arose from a common founder. The age of the mutation in this haplotype was estimated to be around 1850years. The identification of such ‘founder effects’ may greatly simplify diagnostic genetic screening and lead to better prognostic counseling. [ABSTRACT FROM AUTHOR]

Abstract: Objective: Recessive mutations of the SLC26A4 (PDS) gene on chromosome 7q31 can cause sensorineural hearing loss with goiter (Pendred syndrome) or non-syndromic autosomal recessive hearing loss (DFNB4). Furthermore, mutations in the GJB2 gene results in autosomal recessive (DFNB1) and dominant (DFNA3) non-syndromic hearing loss. The aim of the present study was to characterize a family with Pendred syndrome affected by severe to profound HL and presenting goiter. Methods: Affected members underwent detailed audiologic examination and characterization. DNA samples from family members were genotyped with polymorphic microsatellite markers and sequencing of the SLC26A4 and GJB2 genes was performed. A total of 25 families with non-syndromic hearing loss were screened for the common p.E47X mutation in the GJB2 gene by direct dideoxy sequencing. Results: Genetic microsatellite analysis showed linkage to the 7q22–q31 chromosomal region and mutation analysis revealed a novel frameshift mutation (c.451delG) in the SLC26A4 gene. Screening of the GJB2 gene in one patient, displayed a homozygous p.E47X mutation, together with a heterozygous c.451delG mutation. Screening of 25 families with HL showed frequent segregation of the p.E47X mutation, which was homozygous in five of these families. Haplotype analysis using microsatellite markers and single nucleotide polymorphisms (SNPs) closely flanking the GJB2 gene, revealed the presence of two disease-associated-haplotypes suggesting the presence of at least, two founder effects carrying the p.E47X non-sense mutation in the Tunisian population. Conclusions: The segregation of both SLC26A4 and GJB2 mutations in the family illustrates once again the unexpected intra-familial genetic heterogeneity in consanguineous families and highlights the difficulty of genetic counselling in such families. In addition, our results disclose the existence of founder effects in the Tunisian population. [Copyright &y& Elsevier]

Abstract: Biallelic mutations in the GJB2, GJB3, GJB6 and CLDN14 genes have been implicated in autosomal recessive non-syndromic hearing impairment (ARNSHI). Moreover, a large number of GJB2 heterozygous patients was reported. The phenotype was in partly justified by the occurrence of two deletions including GJB6. We analysed GJB2, GJB6, GJB3 and CLDN14 in 102 Tunisian patients with ARNSHI. The deletions del(GJB6-D13S1830) and del(GJB6-D13S1854) were also screened. The c.35delG in GJB2 was the most frequent mutation (21.57%). It was detected at heterozygous state in 2 patients. The del(GJB6-D13S1830) was identified in one case at heterozygous state. No other mutation in studied gap junction genes was detected in heterozygous patients. Several polymorphisms were identified in GJB3, GJB6 and CLDN14. Our study confirms the importance of GJB2 screening in ARNSHI and suggests that in consanguineous populations, a single DFNB1 mutant allele in individuals with HI is likely due to a coincidental carrier state. [Copyright &y& Elsevier]

Abstract: We previously mapped the DFNB66 locus to an interval overlapping the DFNB67 region. Mutations in the LHFPL5 gene were identified as a cause of DFNB67 hearing loss (HL). However, screening of the coding exons of LHFPL5 did not reveal any mutation in the DFNB66 family. The objective of this study was to check whether DFNB66 and DFNB67 are distinctive loci and determining their contribution to HL. In the DFNB66 family, sequencing showed absence of mutations in the untranslated regions and the predicted promoter sequence of LHFPL5. Analysis of five microsatellites in the 6p21.31–22.3 region and screening of the LHFPL5 gene by DNA heteroduplex analysis in DHPLC revealed a novel mutation (c.89dup) in one out of 129 unrelated Tunisian families with autosomal recessive nonsyndromic (ARNS) HL. Our findings suggest that two distinct genes are responsible for DFNB66 and DFNB67 HL. These loci are likely to be a rare cause of ARNSHL. [Copyright &y& Elsevier]

Abstract: Autosomal recessive non-syndromic hearing loss (ARNSHL) is a genetically heterogenous disorder with 41 genes so far identified. Among these genes, ESRRB whose mutations are responsible for DFNB35 hearing loss in Pakistani and Turkish families. This gene encodes the estrogen-related receptor beta. In this study, we report a novel mutation (p.Y305H) in the ESRRB gene in a Tunisian family with ARNSHL. This mutation was not detected in 100 healthy individuals. Molecular modeling showed that the p.Y305H mutation is likely to alter the conformation of the ligand binding-site by destabilizing the coactivator binding pocket. Interestingly, this ligand-binding domain of the ESRRB protein has been affected in 5 out of 6 mutations causing DFNB35 hearing loss. Using linkage and DHPLC analysis, no more mutations were detected in the ESRRB gene in other 127 Tunisian families with ARNSHL indicating that DFNB35 is most likely to be a rare type of ARNSHL in the Tunisian population. [Copyright &y& Elsevier]