Collagen type IV‐related nephropathies in Portugal: pathogenic COL4A5 mutations and clinical characterization of 22 families

Abstract

Alport syndrome (AS) is caused by pathogenic mutations in the genes encoding α3, α4 or α5 chains of collagen IV (COL4A3/COL4A4/COL4A5), resulting in hematuria, chronic renal failure (CRF), sensorineural hearing loss (SNHL) and ocular abnormalities. Mutations in the X-linked COL4A5 gene have been identified in 85% of the families (XLAS). In this study, 22 of 60 probands (37%) of unrelated Portuguese families, with clinical diagnosis of AS and no evidence of autosomal inheritance, had pathogenic COL4A5 mutations detected by Sanger sequencing and/or multiplex-ligation probe amplification, of which 12 (57%) are novel. Males had more severe and earlier renal and extrarenal complications, but microscopic hematuria was a constant finding irrespective of gender. Nonsense and splice site mutations, as well as small and large deletions, were associated with younger age of onset of SNHL in males, and with higher risk of CRF and SNHL in females. Pathogenic COL4A3 or COL4A4 mutations were subsequently identified in more than half of the families without a pathogenic mutation in COL4A5. The lower than expected prevalence of XLAS in Portuguese families warrants the use of next-generation sequencing for simultaneous COL4A3/COL4A4/COL4A5 analysis, as first-tier approach to the genetic diagnosis of collagen type IV-related nephropathies.

Comparison between conventional and comprehensive sequencing approaches for genetic diagnosis of Alport syndrome

“…Although the percentage of patients who were genetically diagnosed with AS did not differ between the conventional Sanger sequencing approach and targeted exome sequencing approach, the proportion of patients with COL4A5 gene mutations was substantially lower (79% and 64%), while the proportion of patients with COL4A3 or COL4A4 variants was correspondingly higher in the NGS group. A higher detection rate in COL4A3 or COL4A4 in the NGS group was similar to recent reports on Southern European populations (Fallerini et al, ; Nabais Sa, Sampaio, et al, ; Nabais Sa, Storey, et al, ). The reason for the higher detection rate in autosomal genes might be due to the inheritance mode of ADAS, which has recently been widely recognized among nephrologists in Japan because of several studies suggesting that the prevalence of ADAS is higher than assumed, not only in Southern European populations, but also in the Japanese population (Fallerini et al, ; Kamiyoshi et al, ; Nabais Sa, Sampaio, et al, ; Nabais Sa, Storey, et al, ).…”

“…In autosomal dominant AS (ADAS), patients usually progress to ESRD later than with ARAS. Although frequencies of these forms have been estimated to be 80% for XLAS, 15% for ARAS, and 5% for ADAS (Kashtan & Segal, ), recent studies have suggested that the proportion of ADAS is greater than previous estimations, especially in Southern European populations (Fallerini et al, ; Moriniere et al, ; Nabais Sa, Sampaio, et al, ; Nabais Sa, Storey, et al, ). It has also been reported that treatment with angiotensin converting enzyme inhibitors can delay development of ESRD.…”

Collagen type IV‐related nephropathies in Portugal: pathogenic COL4A3 and COL4A4 mutations and clinical characterization of 25 families

“…Overall, the two‐stepped molecular analyses of COL4A5 and COL4A3 / COL4A4 in our cohort established the diagnosis of a collagen IV‐related GBM nephropathy in 72.3% of 65 apparently unrelated families; however, only 46.8% of those families with a genetically confirmed diagnosis had XLAS . The lower than expected prevalence of XLAS in our cohort, and the high COL4A3 / COL4A4 / COL4A5 mutation detection rate in patients with fewer than three of the standard diagnostic criteria of AS, are in‐line with the results of recently published Italian and French studies which have used next‐generation sequencing (NGS) to simultaneously screen COL4A5 / COL4A4 / COL4A3 for pathogenic mutations.…”

“…Details of the study design, data collection protocol, patient inclusion criteria and ethics clearance are reported elsewhere . In brief, 40 apparently unrelated probands diagnosed with AS/TBMN, either with a family history suggestive of autosomal inheritance of kidney disease ( n = 5) or without detectable pathogenic mutations in COL4A5 ( n = 35), as screened by Sanger sequencing and multiplex ligation‐dependent probe amplification, were selected for molecular analysis of COL4A3 and COL4A4 .…”

Alport Syndrome

“…Hearing and ocular abnormalities are also more prevalent in men than in women among X-linked AS subjects [20,21]. Sensorineural hearing loss by the age of 30 is found in 60% of male patients with missense mutations compared to 90% of patients with mutations of other more severe types (including splice site mutations) [19].…”