No linkage to the COL4A3 gene locus in Japanese thin basement membrane disease families

Summary: Patients with thin basement membrane disease (TBMD) exhibit persistent haematuria with a diffuse thinning of the glomerular basement membrane (GBM), especially of the lamina densa. It appears to be an autosomal dominant trait. It has been reported that the Goodpasture epitope, which is located in the non-collagenous domain of type IV collagen α 3 chain, may be reduced in patients with TBMD. We speculated that the candidate gene for TBMD could be the type IV collagen α 3 chain gene ( COL4A3 ), which is present closely to type IV collagen α 4 chain gene ( COL4A4 ) on chromosome 2q35–37. We conducted a linkage analysis to investigate the relationship between familial TBMD and COL4A3 gene, using COL4A3 cDNA polymorphism and a (CA)_n microsatellite marker located in the COL4A3 gene. We examined 32 individuals from four Japanese families with TBMD. There were no associations between the patients with haematuria and certain alleles of the two markers in the pedigrees of three families. It has been reported that type IV collagen α 1 chain gene ( COL4A1 ) and α 2 chain gene ( COL4A2 ) are not involved in TBMD, and that α 5 chain gene ( COL4A5 ) and a 6 chain gene ( COL4A6 ) map to chromosome X. In conclusion, our findings suggested that familial TBMD is not caused by the genetic abnormalities of type IV collagen genes isolated thus far.