Abdelhamid Barakat

Mutations in TPRN Cause a Progressive Form of Autosomal-Recessive Nonsyndromic Hearing Loss

We performed genome-wide homozygosity mapping in a large consanguineous family from Morocco and mapped the autosomal-recessive nonsyndromic hearing loss (ARNSHL) in this family to the DFNB79 locus on chromosome 9q34. By sequencing of 62 positional candidate genes of the critical region, we identified a causative homozygous 11 bp deletion, c.42_52del, in the TPRN gene in all seven affected individuals. The deletion is located in exon 1 and results in a frameshift and premature protein truncation (p.Gly15AlafsX150). Interestingly, the deleted sequence is part of a repetitive and CG-rich motive predicted to be prone to structural aberrations during crossover formation. We identified another family with progressive ARNSHL linked to this locus, whose affected members were shown to carry a causative 1 bp deletion (c.1347delG) in exon 1 of TPRN. The function of the encoded protein, taperin, is unknown; yet, partial homology to the actin-caping protein phostensin suggests a role in actin dynamics.

Mutations in the protamine locus: association with spermatogenic failure?

The protamine locus consists of a 28.5 kb region with a linear array of the protamine (PRM)1, PRM2, PRM3 and transition nuclear protein (TNP)2 genes. Several studies indicate an abnormal expression pattern of protamine genes associated with male infertility, although the molecular mechanism underlying this observation is unclear. Here, we determined the spectrum of DNA variants present in all four genes in men with unexplained infertility compared with an ancestry-matched fertile/normospermic population. A total of 160 control individuals and at least 125 infertile men with either idiopathic azoospermia or oligozoospermia were sequenced for the open reading frame of PRM1, PRM2, PRM3 and TNP2 genes. All individuals carried an apparently intact Y chromosome. Of the 28 variants identified, 21 were previously described in the literature. The novel variants that were observed only in the infertile cohort included the SNP c.65G>A mutation which resulted in an amino acid change at the codon 22 (p.Ser22Asn) in the PRM1 gene, a mutation in the promoter region of PRM2 (-67C>T) and a nonsense mutation in the PRM3 gene. These data are consistent with that of previous studies which have indicated that mutations in the protamine locus may be an infrequent cause of male infertility.

Association of Spermatogenic Failure with the b2/b3 Partial AZFc Deletion

Infertility affects around 1 in 10 men and in most cases the cause is unknown. The Y chromosome plays an important role in spermatogenesis and specific deletions of this chromosome, the AZF deletions, are associated with spermatogenic failure. Recently partial AZF deletions have been described but their association with spermatogenic failure is unclear. Here we screened a total of 339 men with idiopathic spermatogenic failure, and 256 normozoospermic ancestry-matched men for chromosome microdeletions including AZFa, AZFb, AZFc, and the AZFc partial deletions (gr/gr, b1/b3 and b2/b3). AZFa and AZFc deletions were identified in men with severe spermatogenic failure at similar frequencies to those reported elsewhere. Gr/gr deletions were identified in case and control populations at 5.83% and 6.25% respectively suggesting that these deletions are not associated with spermatogenic failure. However, b2/b3 deletions were detected only in men with spermatogenic failure and not in the normospermic individuals. Combined with our previous data this shows an association of the b2/b3 deletion (p = 0.0318) with spermatogenic failure in some populations. We recommend screening for this deletion in men with unexplained spermatogenic failure.

Association of the MTHFR A1298C Variant with Unexplained Severe Male Infertility

The methylenetetrahydrofolate reductase (MTHFR) gene is one of the main regulatory enzymes involved in folate metabolism, DNA synthesis and remethylation reactions. The influence of MTHFR variants on male infertility is not completely understood. The objective of this study was to analyze the distribution of the MTHFR C677T and A1298C variants using PCR-Restriction Fragment Length Polymorphism (RFLP) in a case group consisting of 344 men with unexplained reduced sperm counts compared to 617 ancestry-matched fertile or normozoospermic controls. The Chi square test was used to analyze the genotype distributions of MTHFR polymorphisms. Our data indicated a lack of association of the C677T variant with infertility. However, the homozygous (C/C) A1298C polymorphism of the MTHFR gene was present at a statistically high significance in severe oligozoospermia group compared with controls (OR = 3.372, 95% confidence interval CI = 1.27–8.238; p = 0.01431). The genotype distribution of the A1298C variants showed significant deviation from the expected Hardy-Weinberg equilibrium, suggesting that purifying selection may be acting on the 1298CC genotype. Further studies are necessary to determine the influence of the environment, especially the consumption of diet folate on sperm counts of men with different MTHFR variants.

No association between T222P/LGR8 mutation and cryptorchidism in the Moroccan population.

Background: Cryptorchidism is the most common genital anomaly in men. The INSL3/LGR8 system is involved in testicular descent via gubernacular development. INSL3 binds with high affinity to its receptor LGR8 and receptor activation is associated with cAMP signaling. Analysis of human INSL3 and LGR8 mutations confirms that some cases of cryptorchidism are caused by mutations in these genes. The T222P mutation is the only one within the LGR8 gene associated with the cryptorchidism phenotype. A strong association of the T222P mutation with cryptorchidism was found in an Italian population. Due to the same mutation being found in patients within the Mediterranean area, a possible founder effect of this mutation is supposed. Methods: We screened 109 patients with cryptorchidism and 250 controls in a Moroccan population. Results: We found that 3 of the 109 patients tested carry the T222P mutation and 4 individuals in the control group also carry the mutation. Conclusions: Our results show in fact that the same mutation is present in the Moroccan population, but an association between cryptorchidism and the T222P mutation was not found.

Recessive Mutations in RTN4IP1 Cause Isolated and Syndromic Optic Neuropathies

Autosomal-recessive optic neuropathies are rare blinding conditions related to retinal ganglion cell (RGC) and optic-nerve degeneration, for which only mutations in TMEM126A and ACO2 are known. In four families with early-onset recessive optic neuropathy, we identified mutations in RTN4IP1, which encodes a mitochondrial ubiquinol oxydo-reductase. RTN4IP1 is a partner of RTN4 (also known as NOGO), and its ortholog Rad8 in C. elegans is involved in UV light response. Analysis of fibroblasts from affected individuals with a RTN4IP1 mutation showed loss of the altered protein, a deficit of mitochondrial respiratory complex I and IV activities, and increased susceptibility to UV light. Silencing of RTN4IP1 altered the number and morphogenesis of mouse RGC dendrites in vitro and the eye size, neuro-retinal development, and swimming behavior in zebrafish in vivo. Altogether, these data point to a pathophysiological mechanism responsible for RGC early degeneration and optic neuropathy and linking RTN4IP1 functions to mitochondrial physiology, response to UV light, and dendrite growth during eye maturation.

Association of the C677T polymorphism in the human methylenetetrahydrofolate reductase (MTHFR) gene with the genetic predisposition for type 2 diabetes mellitus in a Moroccan population.

AIMS Type 2 diabetes mellitus (T2DM) is a major public health problem around the world. The C677T and A1298C polymorphisms of the methylenetetrahydrofolate reductase (MTHFR) gene have been reported to be associated with T2DM and its complications. This study aimed to investigate this association in the Moroccan population. METHODS A case-control study was performed among 282 Moroccan diabetic patients and 232 healthy controls. The MTHFR C677T and A1298C polymorphisms were genotyped by polymerase chain reaction, followed by enzymatic digestion with HinfI and MboII enzymes, respectively. RESULTS There was a significant association between C677T polymorphism and T2DM in both additive and dominant models. In addition, the 677T allele frequency differed significantly between the diabetic and control groups (26.06% vs. 33.20%, respectively). However, no significant association was found between A1298C polymorphism and T2DM. The frequencies of combined genotypes 677CC/1298AA and 677CT/1298AC differed significantly between the diabetic and control groups (32.62% vs. 20.61% and 9.57% vs. 17.55%, respectively). CONCLUSIONS These results show an evident association between the MTHFR C677T polymorphism and T2DM in Moroccan patients but no significant association with the MTHFR A1298C polymorphism.

Contribution of CDKAL1 rs7756992 and IGF2BP2 rs4402960 polymorphisms in type 2 diabetes, diabetic complications, obesity risk and hypertension in the Tunisian population 在突尼斯人群中，CDKAL1 rs7756992与IGF2BP2 rs4402960的多态性对2型糖尿病、糖尿病并发症、肥胖风险以及高血压的影响

The insulin‐like growth factor 2 mRNA‐binding protein 2 (IGF2BP2) and the cyclin‐dependent kinase 5 regulatory subunit‐associated protein 1‐like 1 (CDKAL1) identified through genome‐wide association (GWA) studies have been shown to be associated with Type 2 diabetes in various ethnic groups. In this study, we investigated the association of the rs7756992 of CDKAL1 and the rs4402960 of IGF2BP2 with Type 2 diabetes, diabetic complications (nephropathy, retinopathy and cardiovascular disease), obesity and hypertension in a Tunisian population.

Prevalence of the mitochondrial A 1555G mutation in Moroccan patients with non-syndromic hearing loss

UNLABELLED Mutations in mitochondrial DNA (mtDNA), especially the A1555G transition in the 12S rRNA gene, are one of the causes of both aminoglycoside-induced and non-syndromic sensorineural hearing loss. OBJECTIVE The aim of this study was to determine the prevalence of the A1555G mitochondrial mutation in Moroccan patients. METHODS We performed molecular characterization by PCR-RFLP and direct sequencing of one hundred and sixty four patients (84 unrelated familial and 80 sporadic cases) with a congenital sensorineural non-syndromic hearing loss and one hundred normal hearing controls for the occurrence of the A1555G mutation. RESULTS Mutational analysis of the mtDNA showed the presence of the homoplasmic A1555G mutation in three families, leading to a frequency of 3.6% similar to that reported for European-populations. No A1555G mutation was detected in sporadic and controls cases. However, we detected in twenty normal hearing controls a novel polymorphism A1557C, which was not found in patient samples. We further evidenced the presence of the A1438G mitochondrial polymorphism in four patients with sensorineural hearing loss and in five controls. CONCLUSION Our results show that the occurrence of the A1555G mutation in hearing impaired patients accounts for 3.6% in a Moroccan patients and those novel mtDNA polymorphisms might contribute to a novel sub-haplogroup specific of the Magrheb.

A novel mutation in the TMC1 gene causes non-syndromic hearing loss in a Moroccan family

Autosomal recessive non-syndromic hearing loss (ARNSHL) is one of the most common genetic diseases in human and is subject to important genetic heterogeneity, rendering molecular diagnosis difficult. Whole-exome sequencing is thus a powerful strategy for this purpose. After excluding GJB2 mutation and other common mutations associated with hearing loss in Morocco, whole-exome sequencing was performed to study the genetic causes of one sibling with ARSHNL in a consanguineous Moroccan family. After filtering data and Sanger sequencing validation, one novel pathogenic homozygous mutation c.1810C>G (p.Arg604Gly) was identified in TMC1, a gene reported to cause deafness in various populations. Thus, we identified here the first mutation in the TMC1 gene in the Moroccan population causing non-syndromic hearing loss.