Three affected individuals were genotyped with HumanOmni2-5Exome-8-v1-1-A (2,583,651 markers) while 8 samples were genotyped with InfiniumOmni2-5Exome-8v1-3_A1 (2,612,357 markers). Genomic DNA was extracted from blood or saliva samples using standard procedures.
Clinical information was obtained from telephone interviews, questionnaires and physician reports. We obtained longitudinal clinical data and eventually blood, saliva, or isolated DNA. Patients were recruited at University Health Network, Toronto, ON, Canada after receiving informed consent in accordance with the hospital Research Ethics Board. Our own local experience has highlighted a preponderance of undiagnosed Alport syndrome but here we describe an unexplained family with FSGS, where our detailed genetic analysis identified an association with segregating heterozygous variants in LAMA2 and LOXL4, whose encoded proteins serve roles in basement membrane assembly and function. The most abundant protein in the glomerular based membrane (GBM) is heterotrimeric type IV collagen (α3α4α5) but there exists numerous other proteins that contribute to GBM architecture and turnover. Through broader sequencing efforts, reports over the past several years have identified an under-recognition of pathogenic variants in type IV collagen, causative for Alport syndrome, in patients presenting with a range of phenotypes spanning from non-progressive haematuria/albuminuria, adult-onset FSGS and classic (severe) disease. ĭefects in basement membrane proteins of the kidney such as those encoded by type IV collagen and LAMβ2 are amongst the monogenic causes of FSGS. Monogenic FSGS has extensive genetic heterogeneity with 59 implicated genes and the list continues to expand, facilitated by the adoption of next-generation sequencing technologies. Thus, our report will be of benefit to the renal community as sequencing in renal disease becomes more widespread.įocal and segmental glomerulosclerosis (FSGS) is a histologic lesion with varied causes which include putative circulating factor(s), monogenic etiologies and hyperfiltering conditions. Alternatively, identification of additional FSGS cases with suspected deleterious variants in LAMA2 and LOXL4 will provide more evidence for disease causality. Limitations to our study includes the absence of functional characterization to support pathogenicity. Conclusionsīased on our findings, we postulate that the additive effect of digenic inheritance of heterozygous variants in LAMA2 and LOXL4 leads to adult-onset FSGS. Examination of basement membranes with electron microscopy showed regions of dense mesangial matrix in one individual and wider glomerular basement membrane (GBM) thickness in two individuals compared to historic control averages. Renal biopsies showed classic segmental sclerosis/hyalinosis lesion on a background of mild mesangial hypercellularity. Two of these variants, in LAMA2 and LOXL4, remained as candidates after segregation analysis and encode extracellular matrix proteins of the glomerulus. WES identified 5 heterozygous rare variants, which were sequenced in 11 relatives where DNA was available. Subsequently, linkage analysis was performed and narrowed the disease gene(s) to within 3% of the genome. Pathogenic variants in known nephropathy genes were excluded. In a family with adult-onset autosomal dominant FSGS, linkage analysis was performed in 11 family members followed by whole exome sequencing (WES) in 3 affected relatives to identify candidate genes. Many genetic causes have been identified in FSGS but even in families with comprehensive testing, a significant proportion remain unexplained. Focal and segmental glomerulosclerosis (FSGS) is a histologic pattern of injury that characterizes a wide spectrum of diseases.
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