Novel compound heterozygous variants in NBAS underlying fever-dependent infantile liver failure syndrome type 2: potential implications of protein thermostability.

Background & aims: Infant liver failure syndrome type 2 (ILFS2), a rare autosomal recessive disorder manifesting as recurrent acute liver failure (ALF) triggered by febrile illness, is associated with neuroblastoma amplified sequence (NBAS) mutations. This study employs molecular dynamics simulation (MDS) to investigate how missense variants in the Sec39 domain influence protein conformation and thermostability.

Approach & results: We identified novel compound heterozygous variants in the NBAS gene, c.2231 T > C (p.Leu744Pro) and c.2266C > T (p.Arg756Cys), in two Chinese siblings diagnosed with ILFS2. According to ACMG guideline, both variants were initially classified as variants of uncertain significance. To elucidate the potential functional impact, MDS was performed to compare structural dynamics between wild-type (WT) and mutant (MUT) NBASs at physiological temperature (37°C) and under thermal stress (42°C). The results revealed distinct thermal responses. WT demonstrated robust thermotolerance, with comparable trajectory patterns and curve parameters across two temperatures. In contrast, specific variants induced localized conformational perturbations and secondary structural reorganization. Notably, while MUT exhibited kinetic profiles similar to WT at 37°C, it showed pronounced fluctuations in flexible regions under thermal stress, with disrupted hydrogen-bonding networks and significant conformational changes, indicating compromised thermostability.

Conclusions: The diagnosis of ILFS2 primarily relies on clinical presentation and genetic confirmation. Although the exact pathogenesis remains unclear, our findings suggest that temperature-sensitive structural destabilization induced by missense mutations within the Sec39 domain of NBAS probably underlies the fever-associated ALF. This provides critical guidance for subsequent protein structural elucidation and mechanism research, and regions exhibiting significantly reduced thermostability represent promising therapeutic targets.