Characterization of a novel MYO3A missense mutation associated with a dominant form of late onset hearing loss.

Whole-exome sequencing of samples from affected members of two unrelated families with late-onset non-syndromic hearing loss revealed a novel mutation (c.2090 T > G; NM_017433) in MYO3A. The mutation was confirmed in 36 affected individuals, showing autosomal dominant inheritance. The mutation alters a single residue (L697W or p.Leu697Trp) in the motor domain of the stereocilia protein MYO3A, leading to a reduction in ATPase activity, motility, and an increase in actin affinity. MYO3A-L697W showed reduced filopodial actin protrusion initiation in COS7 cells, and a predominant tipward accumulation at filopodia and stereocilia when coexpressed with wild-type MYO3A and espin-1, an actin-regulatory MYO3A cargo. The combined higher actin affinity and duty ratio of the mutant myosin cause increased retention time at stereocilia tips, resulting in the displacement of the wild-type MYO3A protein, which may impact cargo transport, stereocilia length, and mechanotransduction. The dominant negative effect of the altered myosin function explains the dominant inheritance of deafness.

Novel partial duplication of EYA1 causes branchiootic syndrome in a large Brazilian family.

OBJECTIVE: To identify novel genetic causes of syndromic hearing loss in Brazil. DESIGN: To map a candidate chromosomal region through linkage studies in an extensive Brazilian family and identify novel pathogenic variants using sequencing and array-CGH. STUDY SAMPLE: Brazilian pedigree with individuals affected by BO syndrome characterized by deafness and malformations of outer, middle and inner ear, auricular and cervical fistulae, but no renal abnormalities. RESULTS: Whole genome microarray-SNP scanning on samples of 11 affected individuals detected a multipoint Lod score of 2.6 in the EYA1 gene region (chromosome 8). Sequencing of EYA1 in affected patients did not reveal pathogenic mutations. However, oligonucleotide-array-CGH detected a duplication of 71.8Kb involving exons 4 to 10 of EYA1 (heterozygous state). Real-time-PCR confirmed the duplication in fourteen of fifteen affected individuals and absence in 13 unaffected individuals. The exception involved a consanguineous parentage and was assumed to involve a different genetic mechanism. CONCLUSIONS: Our findings implicate this EYA1 partial duplication segregating with BO phenotype in a Brazilian pedigree and is the first description of a large duplication leading to the BOR/BO syndrome.

c.G2114A MYH9 mutation (DFNA17) causes non-syndromic autosomal dominant hearing loss in a Brazilian family.

We studied a family presenting 10 individuals affected by autosomal dominant deafness in all frequencies and three individuals affected by high frequency hearing loss. Genomic scanning using the 50k Affymetrix microarray technology yielded a Lod Score of 2.1 in chromosome 14 and a Lod Score of 1.9 in chromosome 22. Mapping refinement using microsatellites placed the chromosome 14 candidate region between markers D14S288 and D14S276 (8.85 cM) and the chromosome 22 near marker D22S283. Exome sequencing identified two candidate variants to explain hearing loss in chromosome 14 [PTGDR - c.G894A:p.R298R and PTGER2 - c.T247G:p.C83G], and one in chromosome 22 [MYH9, c.G2114A:p.R705H]. Pedigree segregation analysis allowed exclusion of the PTGDR and PTGER2 variants as the cause of deafness. However, the MYH9 variant segregated with the phenotype in all affected members, except the three individuals with different phenotype. This gene has been previously described as mutated in autosomal dominant hereditary hearing loss and corresponds to DFNA17. The mutation identified in our study is the same described in the prior report. Thus, although linkage studies suggested a candidate gene in chromosome 14, we concluded that the mutation in chromosome 22 better explains the hearing loss phenotype in the Brazilian family.

Obesity and variants of the GHRL (ghrelin) and BCHE (butyrylcholinesterase) genes.

Ghrelin coded by the GHRL gene is related to weight-gain, its deactivation possibly depending on its hydrolyzation by butyrylcholinesterase (BChE) encoded by the BCHE gene, an enzyme already associated with the body mass index (BMI). The aim was to search for relationships between SNPs of the GHRL and BCHE genes with BChE activity, BMI and obesity in 144 obese and 153 nonobese Euro-Brazilian male blood donors. In the obese individuals, a significant association with higher BChE activity, in the 72LM+72MM; -116GG genotype class (GHRL and BCHE genes, respectively) was noted. No significant differences were found otherwise, through comparisons between obese and control individuals, of genotype and allele frequencies in SNPs of the GHRL gene (Arg51Gln and Leu72Met), or mean BMI between 72LL and 72LM+72MM genotypes. Although there appears to be no direct relationship between the examined GHRL SNPs and BMI, the association of the 72M SNP with higher BChE activity in obese subjects probably points to a regulatory mechanism, thereby implying the influence of the GHRL gene on BChE expression, and a consequential metabolic role in the complex process of fat utilization.

Obesity and variants of the GHRL (ghrelin) and BCHE (butyrylcholinesterase) genes

Ghrelin coded by the GHRL gene is related to weight-gain, its deactivation possibly depending on its hydrolyzation by butyrylcholinesterase (BChE) encoded by the BCHE gene, an enzyme already associated with the body mass index (BMI). The aim was to search for relationships between SNPs of the GHRL and BCHE genes with BChE activity, BMI and obesity in 144 obese and 153 nonobese Euro-Brazilian male blood donors. In the obese individuals, a significant association with higher BChE activity, in the 72LM+72MM; -116GG genotype class (GHRL and BCHE genes, respectively) was noted. No significant differences were found otherwise, through comparisons between obese and control individuals, of genotype and allele frequencies in SNPs of the GHRL gene (Arg51Gln and Leu72Met), or mean BMI between 72LL and 72LM+72MM genotypes. Although there appears to be no direct relationship between the examined GHRL SNPs and BMI, the association of the 72M SNP with higher BChE activity in obese subjects probably points to a regulatory mechanism, thereby implying the influence of the GHRL gene on BChE expression, and a consequential metabolic role in the complex process of fat utilization.