Mutation Analysis of Thin Basement Membrane Nephropathy

Abstract

Thin basement membrane nephropathy (TBMN) is characterized by the observation of microhematuria and a thin glomerular basement membrane on kidney biopsy specimens. Its main cause is heterozygous mutations of COL4A3 or COL4A4, which also cause late-onset focal segmental glomerulosclerosis (FSGS) or autosomal dominant Alport syndrome (ADAS). Thirteen TBMN cases were analyzed using Sanger sequencing, multiplex ligation-dependent probe amplification (MLPA), and exome sequencing. Ten heterozygous variants were detected in COL4A3 or COL4A4 in nine patients via Sanger sequencing, three of which were novel variants. The diagnostic rate of "likely pathogenic" or "pathogenic" under the American College of Medical Genetics and Genomics guidelines was 53.8% (7 out of 13 patients). There were eight single nucleotide variants, seven of which were glycine substitutions in the collagenous domain, one of which was a splice-site single nucleotide variant, and two of which were deletion variants. One patient had digenic variants in COL4A3 and COL4A4. While MLPA analyses showed negative results, exome sequencing identified three heterozygous variants in causative genes of FSGS in four patients with no apparent variants on Sanger sequencing. Since patients with heterozygous mutations of COL4A3 or COL4A4 showed a wide spectrum of disease from TBMN to ADAS, careful follow-up will be necessary for these patients.

Keywords: COL4A3; COL4A4; autosomal dominant Alport syndrome; microhematuria; mutation; thin basement membrane nephropathy; variant.

Figure 1

Heterozygous variants of COL4A3 or COL4A4 identified in the present study. Of 10 variants in COL4A3 or COL4A4, 8 were single nucleotide variants and 2 were deletion variants. There was a splice-site single nucleotide variant in Patient 6. Patient 1 had digenic variants (COL4A3 c.469G > C and COL4A4 c.2510G > C).

Figure 2

Multiplex ligation-dependent probe amplification (MLPA) analyses of COL4A3 and COL4A4. MLPA analyses showed negative results in four patients with no apparent variants for Sanger sequencing.