Autosomal Dominant Alport's Syndrome : study of a large Tunisian family

Alport's syndrome is a hereditary nephritis that may lead to end-stage renal disease (ESRD) in early adult life. It is a clinically and genetically heterogeneous nephropathy. Alport's syndrome is often associated with sensorineural deafness and / or ocular abnormalities. In contrast with the well-known X-linked phenotype, very little is known about the autosomal dominant form caused by mutations in COL4A3 and COL4A4 in the chromosome region 2q35-q37. We describe a Tunisian family with autosomal dominant Alport's syndrome in which males and females were equally affected. Two members reached ESRD at age 40 and 53 years, respectively. Three members experienced isolated microhematuria and one member experienced sensorineural deafness. No eye abnormalities were observed. Immunohistochemical studies showed a normal distribution of the α5 (type IV collagen) chain in the epidermal basement membrane. Genetic analysis demonstrated that a common haplotype co-segregated with the disease in the heterozygous state in all affected patients, thereby, confirming an autosomal dominant mode of inheritance. The same haplotype was observed in two asymptomatic children. We conclude that autosomal dominant Alport's syndrome, follows a rare mode of inheritance and exhibits a milder phenotype than usually observed in classic X-linked Alport's syndrome. The frequency of this mode of inheritance should be confirmed by a larger study.