Alport syndrome

The diagnosis of Alport syndrome is suspected from the clinical features and confirmed by identifying the almost pathognomonic ultrastructural changes to the basement membrane in a family member with early disease (so that glomeruli are not too sclerosed), or in modern times by identifying a causative mutation in one or more of the three implicated COL4 genes. Genetic testing is becoming simpler and cheaper, but is still out of the reach of many. Eighty-five per cent of cases are caused by COL4A5 mutations and 10–15% by autosomal recessive disease. A significant proportion of morbidity in X-linked disease occurs in female ‘carriers’ heterozygous for the disease. Changes by light microscopy are non-specific, and can be misleading unless accompanied by electron microscopy. Immunohistology can be helpful but may not be definitive as some causative mutations are not associated with absence of protein product. As COL4A5 is expressed in skin, skin studies are theoretically useful, but they are technically challenging and only a definite negative result is helpful. It is important to distinguish other disorders causing renal disease with deafness, and other causes of glomerular haematuria. Two rare syndromes are caused by extended deletions beyond the COL4A5 gene: X-linked Alport syndrome with diffuse oesophageal leiomyomatosis in which smooth muscle leoimyomas is transmitted in a dominant fashion, and X-linked Alport syndrome with mental retardation.