Molecular and clinical analysis of the most frequent European Alport syndrome variant

Principal Investigator

Scientific interest within the context of the graduate college:

Not Everything Is “Genetic”, but Genes Are Involved in Everything (adapted from Kenneth M. Weiss). Our group is interested in identification and investigation of genetic, clinical, and environmental factors determining onset of chronic kidney disease (CKD) and kidney survival. We make use of next-generation sequencing techniques and deep-phenotyping to identify genetic variants that are predictive for disease progression or convey protection from organ failure. We functionally evaluate identified germline variants in vitro in order to understand underlying molecular mechanisms leading to CKD on the one hand or protecting from kidney failure on the other. By doing so, we aim at defining and targeting molecular switches responsible for health maintenance and disease alleviation.

Project description:

Alport syndrome (AS) is one of the most common genetic kidney diseases. On the renal level, AS is characterized by proteinuria, hematuria, and progressive kidney function decline over lifetime. Beyond the kidney, affected individuals may suffer from sensorineural deafness and eye involvement, such as retinopathy, cataract and lenticonus. AS is caused by germline mutations in three disease genes: COL4A3, COL4A4, and COL4A5. While mutations in the latter lead to X-linked AS with a male preponderance, defects in COL4A3 and COL4A4 result in the autosomal forms, either with a dominant or recessive inheritance pattern. There is one single gene variant in COL4A5 accounting for about 16% of all AS-cases in our datasets: COL4A5-Gly624Asp.¹ This variant constitutes a founder mutation originating from Eastern Europe. Interestingly, we and others found that it is associated with a significantly milder course of disease: median age at kidney failure between 20-30 years later than in carriers of other COL4A5 missense mutations.^1,2 However, the molecular effect of the most common disease causing COL4A5 variant has not been investigated to date and it is unknown why it is somehow less damaging than other protein variants. On the other hand, we observe a phenomenon called intra- and inter-familial variability among carriers of COL4A5-Gly624Asp, leaving the possibility of environmental and epigenetic modification. To address this question, we propose the following two specific aims and work packets (WP):

Aim 1 / WP1: Clinical cohort expansion and functional comparison of COL4A5-Gly624Asp compared to other COL4A5-missense variants. With the help of the European Reference Network (ERKNet), we aim to identify and clinically characterize additional patients with COL4A5-Gly624Asp. Functionally, we would like to run in vitro assays in overexpression systems (such as Western Blotting /Co-IP, by use of HEK293T) for systematic comparison of COL4A5-Gly624Asp with other Gly- and non-Gly missense variants. Thereby, we aim to see differences in residual protein function, stability, and protein interaction compared to other COL4A4/A3/A5 mutant and wildtype constructs.

Aim 2 / WP2: Epigenetic comparison of monozygotic twins with the COL4A5-Gly624Asp variant. DNA methylation is an epigenetic modification that plays an important role in regulating gene expression. Within our in-house AS-cohort (n> 200), we have a unique opportunity to investigate this research question by examining divergent disease progression in monozygotic twins carrying the identical COL4A5 Gly624Asp variant, yet exhibiting markedly different disease severity (CKD stage G3a in one twin versus CKD stage G5 in the other, both at 32 years of age).We would like to investigate their existing kidney biopsy material (kidney tissue) for methylome-wide differences potentially explaining discrepancies in clinical course (in collaboration with Dr. rer. nat. Antje Richter, expert on epigenetics at the Justus-Liebig University in Giessen).

Application details

References