Brahim El Houate

Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis

Atopic disease, including atopic dermatitis (eczema), allergy and asthma, has increased in frequency in recent decades and now affects ∼20% of the population in the developed world. Twin and family studies have shown that predisposition to atopic disease is highly heritable. Although most genetic studies have focused on immunological mechanisms, a primary epithelial barrier defect has been anticipated. Filaggrin is a key protein that facilitates terminal differentiation of the epidermis and formation of the skin barrier. Here we show that two independent loss-of-function genetic variants (R510X and 2282del4) in the gene encoding filaggrin (FLG) are very strong predisposing factors for atopic dermatitis. These variants are carried by ∼9% of people of European origin. These variants also show highly significant association with asthma occurring in the context of atopic dermatitis. This work establishes a key role for impaired skin barrier function in the development of atopic disease.

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.

Y-chromosome AZFc structural architecture and relationship to male fertility

OBJECTIVE To determine if there is a relationship between various forms of partial AZFc deletions and spermatogenic failure. DESIGN Case-control study. SETTING Infertility clinic (Tenon Hospital, Paris). PATIENT(S) 557 men, comprising 364 infertile men from mixed ethnic backgrounds, and 193 men with known fertility (n = 84) and/or normospermic (n = 109). INTERVENTION(S) Characterization of 32 partial AZFc deletions. MAIN OUTCOME MEASURE(S) DAZ gene cluster divided into two families (DAZ1/2 and DAZ3/4), CDY1 gene, and Y-chromosome haplogroups. RESULT(S) We observed 18 partial AZFc deletions in 364 (4.95%) infertile men compared with 14 out of 193 (7.25%) in the control normospermic/fertile group. CONCLUSION(S) The analysis of informative Y-chromosome single nucleotide variants combined with Y-chromosome haplogroup definition enabled us to infer seven deletion classes that occur on a minimum of six Y-chromosome parental architectures. We found no relationship between either the presence or the absence of DAZ1/2, DAZ3/4, CDY1a, or CDY1b with spermatogenic failure at least on one Y-chromosome lineage. The DAZ dosage and Southern blot analyses indicated that the majority of individuals tested carried two copies of the DAZ gene, indicating a partial AZFc deletion. Our data are consistent with the hypothesis that, at least in our study populations, partial AZFc deletions may have a limited impact on fertility.

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.

Mutation rate at 17 Y-STR loci in “Father/Son” pairs from moroccan population

Precise knowledge of mutation rate at Y-STRs loci is essential for a correct evaluation of typing results in forensic casework and specially kinship genetic studies. In this study, we have examined 252 confirmed and unrelated father/son sample pairs from Moroccan population using the 17 Y-STR markers DYS19, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS385a, DYS385b, DYS437, DYS438, DYS439, DYS448, DYS456, DYS458, DYS635, and Y-GATA-H4 of the AmpFlSTR Yfiler™ kit used in routine casework. We observed a total of 15 single repeat mutations between fathers and sons as mutational events. Nine mutations resulted in the gain of a repeat in the son and six resulted in a loss of a repeat. The average mutation rate in the studied sample is 3.5×10(-3) (95% CI 2-5.8×10(-3)). Furthermore, Y-STRs mutation occurrence seems to be 4 times more frequent than autosomal STRs mutation in this sample.

Y Chromosome Microdeletions and Haplotypes

The human Y chromosome contains a number of genes and gene families that are necessary for spermatogenesis. Many of these genes are embedded in repetitive elements that are subject to deletion events. Deletions of azoospermia factor (AZF) regions AZFa, AZFb, and AZFc are found in approx 10–15% of men with either unexplained severe oligozoospermia or azoospermia. These deletions fall on different Y chromosome backgrounds and there is no evidence for a link between a Y-chromosome lineage and the presence or absence of an AZF deletion. Several partial AZFc deletions have been described. One of these, which removes around half of all the genes within the AZFc region, appears to be present as in inconsequential polymorphism in populations of northern Eurasia. A second deletion, termed gr/gr, results in the absence of several AZFc genes and has been suggested to be a genetic risk factor for spermatogenic failure. However, the link between the gr/gr deletion and infertility is more complex. First, the gr/gr deletion is actually not a single type of deletion but a combination of deletions that vary in size and complexity and result in the absence of different members of the deleted azoospermia (DAZ) gene family as well as other AZFc genes, such as CDY1. Second, there are regional or ethnic differences in the frequency of gr/gr deletions. In some Y-chromosome lineages, these deletion appear to be fixed and may have little influence on spermatogenesis. Third, these observations have influenced a number of association studies aimed to determine the relationship between the gr/gr deletion and male infertility. Consequently, some studies suggest that the gr/gr deletion confers a strong genetic susceptibility to reduced sperm counts, whereas others suggest that the genetic susceptibility may not exist or be limited to specific Y-chromosome haplotypes.