Genome-wide association study of longitudinal urinary albumin excretion in patients with type 1 diabetes

Identifying genetic determinants for longitudinal changes in albumin excretion in individuals with type 1 diabetes may help identify those that are predisposed to renal, retinal and cardiovascular complications. Most studies have focussed on genetic predisposition to diabetic kidney disease and used cross-sectional measurements of urinary albumin excretion, but with limited success. Here, we utilise the wealth of longitudinal data and bio-samples collected from cohorts of childhood-onset type 1 diabetes followed over the last 30 years to describe a novel trajectory phenotype quantifying urinary albumin excretion changes during childhood and adolescence. We conducted a genome-wide association study and fine-mapping analysis for albumin excretion in 1584 individuals, finding one signal for cross-sectional albumin excretion close to GALNTL6 (rs150766792), which validated in a previous independent study, and a novel genome-wide significant signal for albumin excretion trajectory in the CDH18 gene region (rs145715205). Our trajectory phenotype quantifies albumin progression and offers a complementary measure to an albumin excretion phenotype based on a single measurement (i.e. most recent data collection) or an average of repeated measurements in longitudinal studies. It can be used to identify genetic or other risk factors which predict better or worse prognosis, thus facilitating the development of new preventive and therapeutic approaches.