In vitro functional analyses can aid precision diagnostics of HNF1B-MODY

Precision medicine relies on accurate and consistent classification of sequence variants. A correct diagnosis of HNF1B-MODY, caused by pathogenic variants in the HNF1B gene, is important for optimal disease management and prognosis, and has implications for genetic counseling and follow-up of at-risk family members. In the present study, the hypothesis is that the functional characterization could provide valuable information to assist the interpretation of pathogenicity of HNF1B variants. Using different in vitro functional assays, seven variants were analyzed identified among 313 individuals suspected to have monogenic diabetes with or without kidney disease. The data from the functional assays were subsequently conjugated with obtained clinical, biochemical, and in silico data. Two variants (p.A167P, p.H336Pfs*22) showed severe loss-of-function due to impaired transactivation, reduced DNA binding (p.A167P), and mRNA instability (p.A167P). While both these variant carriers were diagnosed with diabetes, the p.H336Pfs*22 carrier also had congenital absence of a kidney, which is a characteristic HNF1B-MODY trait. Functional analysis of the p.A167P variant revealed damaging effects on HNF-1B protein function, which may warrant imaging of the kidneys and/or pancreas. In addition, the current study has generated important data, including evidence supporting the benign functional impact of five variants (p.D82N, p.T88A, p.N394D, p.V458G and p.T544A), and piloting new approaches that will prove critical for the growth of HNF1B-diabetes diagnosis.