#2438 ADPKD and collagen genes (COL4A3, COL4A4, COL4A5)
Authors: Caprara Carlotta , Corradi Valentina , Rigato Matteo , Mancini Barbara , Marzano Nenzi , Perbellini Omar , Gastaldon Fiorella , Ronco Claudio , Zanella Monica 
Published: May 2024

Abstract

Background and Aims
Familial hematuria diseases are a heterogeneous group of monogenic conditions caused by mutations in one of the collagen IV genes: COL4A3 (2q36.3), COL4A4 (2q36.3), and COL4A5 (Xq22.3) that are expressed in the glomerular basement membranes (GBM) and are responsible for the most frequent forms of microscopic hematuria (MH), Alport syndrome, and thin basement membrane nephropathy (TBMN).
Recent data suggest that about 1% (1 in 106 individuals) of the world population may have heterozygous predicted pathogenic COL4A3 or COL4A4 variants, a frequency that leads to the occasional superimposition of TBMN with other glomerulopathies.
Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a major genetic disorder affecting up to 12.5 million individuals worldwide and it is the fourth most common global cause of renal replacement therapy. Two are the principal causative genes: PKD1(16p13.3) and PKD2 (4q22.1).
The aim of the study was to describe a cohort of clinically ADPKD patients studying collagen IV genes COL4A3, COL4A4, and COL4A5.

Method
We performed NGS with Sophia Genetic “Nephropathies Solution” Panel on clinically ADPKD patients (pts). This panel includes 44 genes (target region 105.8 kb) involved in different types of nephropathies.
We considered variants that are categorized as Variant of Uncertain Significance (Vus), likely pathogenic, or pathogenic (Class 3,4, or 5 of American College of Medical Genetics (ACMG)) in COL4A3, COL4A4, and COL4A5 genes.

Results
We analyzed 250 consecutive clinically ADPKD pts (consecutive in the outpatient clinic).
We found 13 (6.3%) clinically potentially interesting (Class 3,4 or 5 of ACMG) variants in collagen genes.
We found 2 pts that were negative for PKD1, PKD2, PKHD1 analysis: 1 pt carrier COL4A4 NM_000092.5: c.2908C&gt;T (p.Gln970Ter), Pathogenic and c.2756A&gt;G (p.Glu919Gly) Vus; 1 male pt carrier COL4A3 NM_000091.5: c.609+3_609+6del, Vus and COL4A5 NM_000495:c.169G&gt;A p.(Gly57Arg), likely pathogenic.
We also found 4 pts with 4 Vus variants in collagens genes combined with at least 1 pathogenic or likely pathogenic variant in PKD1 or PKD2 genes.
We found 3 pts with likely pathogenic variants in COL4A4 or COL4A3 genes combined with Vus or likely benign variants in PKD1 or PKD2 genes and 1 patient with 1 likely pathogenic variant in COL4A3 and 1 likely pathogenic variant in PKD1.

Conclusion
Variants in collagen genes are very frequent and the associated phenotype is varied, sometimes very mild such as microhematuria. Furthermore, penetrance has to be considered. The study outlines the importance of considering also collagen genes, even if we have a clear clinical manifestation of ADPKD. An additional variant in a kidney already compromised can have an impact on the phenotype. Analysis of genes involved in these 2 pathologies could lead to a better understanding of the phenotype-genotype correlation at least in patients with both conditions.