Functional analysis of novel and recurrent RINT1 variants in patients with infantile liver dysfunction

Area of Science:

• Genetics
• Molecular Biology
• Hepatology

Background:

• Rad50-interacting protein (RINT1) is crucial for membrane trafficking and lipid metabolism, interacting with ER tethering and SNARE complexes.
• Loss-of-function RINT1 variants are linked to episodic transaminitis, skeletal dysplasia, or spastic paraplegia.

Purpose of the Study:

• To investigate the molecular mechanisms underlying liver disease caused by RINT1 variants.
• To characterize the functional consequences of identified RINT1 variants in patients and model systems.

Main Methods:

• Trio-whole-exome sequencing to identify pathogenic variants in patients.
• Immunoprecipitation to assess protein interactions.
• Quantitative PCR (qPCR) to analyze gene expression.
• Autophagic flux assays (LC3-II turnover).
• Drosophila melanogaster models for in vivo functional studies.

Main Results:

• Two unrelated patients with recurrent transaminitis, coagulopathy, and hyperammonemia were found to have biallelic pathogenic RINT1 variants.
• Mutant RINT1 proteins exhibited disrupted ER tether and SNARE interactions.
• RINT1 dysfunction activated the unfolded protein response (UPR) and impaired autophagic flux.
• Drosophila models showed tissue atrophy and reduced lipid droplets in the fat body.

Conclusions:

• Loss of RINT1 function contributes to liver disease pathogenesis through UPR activation, impaired autophagy, and lipid storage abnormalities.
• RINT1 variants disrupt essential cellular processes, leading to severe liver manifestations.