Collagen type IV nephropathy: Genetic heterogeneity examinations in affected Hungarian families

Abstract

The Col4A3, Col4A4 and Col4A5 collagen type IV genes are found to be mutated in Col IV nephropathy. In males with a mutation in the Col4A5 gene (X-linked Alport syndrome: XL-AS), progressive renal disease always develops. Female carriers with a mutation in the Col4A5 gene can develop thin basement membrane nephropathy (TBMN). Males and females who carry 1 Col4A3 or Col4A4 mutation usually manifest TBMN with nonprogressive hematuria. In the event of 2 Col4A3 or Col4A4 gene mutations, the autosomal recessive AS will develop. We examined the cosegregation pattern of hematuria in 20 families. The renal biopsies led to diagnoses of AS in 7 families, and of TBMN in 6 families. In 7 others, the diagnosis of familial hematuria (FHU) was based on the clinical symptoms. Markers of the ColA3/Col4A4 and Col4A5 loci (Col4A3: CA11 and D2S401; Col4A4: HaeIII/RFLP; and Col4A5: DXS456, 2B6 and 2B20) were used to assess their linkage to the clinical symptoms and morphological alterations. Maximum likelihood and the FASTLINK version of the linkage program were applied to compute logarithm of the odds (LOD) scores. A linkage to the Col4A3/Col4A4 genes was identified in 5 families (FHU in 3, AS in 2 families, 25%, LOD score range: 0.20–3.51). The XL-AS pattern of inheritance seemed likely with Col4A5 in 9 families (45%, LOD: 0.43–4.20); we found 4 disease-causative mutations by high-resolution melting curve analysis (LC480) and sequencing in this group. In 2 FHU families, the linkage to chromosomes 2 and X was precluded. Knowledge of the genetic background of Col IV nephropathy is essential to avoid the misdiagnosis of FHU and early AS. The allele frequencies, heterozygosity content and polymorphism information content of the applied STR markers on unrelated Hungarian normal and affected chromosomes 2 and X were also calculated.