A genotype-phenotype correlation in Sicilian patients with GJB2 biallelic mutations.

The aim of this work was to study the genotype distribution of Sicilian patients with biallelic GJB2 mutations; to correlate genotype classes and/or specific mutations of GJB2 gene (35delG-non-35delG) with audiologic profiles. A total of 10 different mutations and 11 different genotypes were evidenced in 73 SNHL subjects; 35delG (90.36 % of cases) and IVS1+1 (13.69 %) were the most common mutations found in the cohort with a significant difference in the distribution between North and South Sicily. Audiological evaluation revealed a severe (16/73) to profound (47/73) hearing loss (HL) in 86.13 % of cases without significant difference between the degree of HL and the province of origin of the subjects (P = 0.727). The homozygous truncating (T/T) genotype was the most widespread (89.04 % of cases), with a severe-to-profound hearing impairment in 90.36 % of T/T class with respect to truncating/non-truncating (T/NT) and non-truncating/non-truncating (NT/NT) genotypes (P = 0.012). From the comparison of homozygous 35delG and 35delG/non-35delG genotypes, a more profound HL in the homozygous 35delG than in compound heterozygous 35delG/non-35delG (p < 0.0001) resulted. This study confirms that 35delG is the most common mutation in the Mediterranean area with a heterogeneous distribution of the genotypes between North and South Sicily; probands homozygotes for 35delG or presenting a T/T genotype are more apt to have a severe-to-profound HL.

Identification of D179H, a novel missense GJB2 mutation in a western Sicily family.

The main purpose of this study was to describe a novel missense mutation (p.D179H) found in a Western Sicily family and to examine the genetic and audiologic profiles of all family members by performing a GJB2 and GJB6 mutations analysis and a complete audiologic assessment. The proband was a 3-month-old infant with a congenital profound sensorineural hearing loss; direct sequencing of the GJB2 revealed the presence of a c.35delG mutation in the heterozygous state and a heterozygous G>C transition at nucleotide 535 in trans; this novel mutation, called p.D179H, resulted in an aspartic acid to histidine change at codon 179. It was also evidenced in the heterozygous state in two members of this family, both with normal hearing. No GJB6 mutations were evidenced in all subjects studied. Considering the genotypic and phenotypic analysis of all family members, we suggest, differently from the p.D179 N mutation previously reported, a recessive mode of inheritance. Functional studies on p.D179H have to be performed to confirm our hypothesis.

High variability of Fabry disease manifestations in an extended Italian family.

Fabry disease (FD) is an inherited metabolic disorder caused by partial or full inactivation of the lysosomal hydrolase α-galactosidase A (α-GAL). The impairment of α-GAL results in the accumulation of undegraded glycosphingolipids in lysosomes and subsequent cell and microvascular dysfunctions. This study reports the clinical, biochemical, and molecular characterization of 15 members of the same family. Eight members showed the exonic mutation M51I in the GLA gene, a disease-causing mutation associated with the atypical phenotype. The clinical history of this family highlights a wide phenotypic variability, in terms of involved organs and severity. The phenotypic variability of two male patients is not related to differences in α-GAL enzymatic activity: though both have no enzymatic activity, the youngest shows severe symptoms, while the eldest is asymptomatic. It is noticeable that for two female patients with the M51I mutation the initial clinical diagnosis was different from FD. One of them was diagnosed with Familial Mediterranean Fever, the other with Multiple Sclerosis. Overall, this study confirms that the extreme variability of the clinical manifestations of FD is not entirely attributable to different mutations in the GLA gene and emphasizes the need to consider other factors or mechanisms involved in the pathogenesis of Fabry Disease.

De novo mutation in a male patient with Fabry disease: a case report.

BACKGROUND: Fabry disease is an X-linked inherited metabolic condition where the deficit of the α-galactosidase A enzyme, encoded by the GLA gene, leads to glycosphingolipid storage, mainly globotriaosylceramide. To date, more than 600 mutations have been identified in human GLA gene that are responsible for FD, including missense and nonsense mutations, small and large deletions. Such mutations are usually inherited, and cases of de novo onset occur rarely. CASE PRESENTATION: In this article we report an interesting case of a 44-year-old male patient suffering from a severe form of Fabry disease, with negative family history. The patient showed signs such as cornea verticillata, angiokeratomas, cardiac and neurological manifestations, an end-stage renal disease and he had low α-galactosidase A activity. We detected, in this subject, the mutation c.493 G > C in the third exon of the GLA gene which causes the amino acid substitution D165H in the protein. This mutation affects the amino acid - belonging to the group of buried residues - involved, probably, in the preservation of the protein folding. Moreover, studies of multiple sequence alignment indicate that this amino acid is highly conserved, thus strengthening the hypothesis that it is a key amino acid to the enzyme functionality.The study of the relatives of the patient showed that, surprisingly, none of the members of his family of origin had this genetic alteration, suggesting a de novo mutation. Only his 11-year-old daughter - showing acroparaesthesias and heat intolerance with reduced enzymatic activity - had the same mutation. CONCLUSIONS: We suggest that a non-inherited mutation of the α-galactosidase A gene is responsible for Fabry disease in the patient who had reduced enzyme activity and classical clinical manifestations of the disease. In a family, it is rare to find only one Fabry disease affected subject with a de novo mutation. These findings emphasize the importance of early diagnosis, genetic counselling, studying the genealogical tree of the patients and starting enzyme replacement therapy to prevent irreversible vital organ damage that occurs during the course of the disease.