Introduction Following its first description in 2015, NBAS deficiency has become an established, monogenic cause of recurrent acute liver failure (ALF). Acute liver failure is characteristically triggered by fever and its pathobiology has been linked to a disruption in retrograde transport between the Golgi and endoplasmic reticulum. Previous in vitro experiments demonstrated that application of stress by heat caused reduced protein expression and function. A second mechanism proposed is a disruption in nonsense-mediated mRNA decay (NMD), a highly conserved post-transcriptional regulatory mechanism of gene expression in eukaryotes. The purpose of this work was to further characterise the pathobiology of NBAS deficiency and evaluate whether NMD is disrupted using the endogenous NMD targets, GADD45A and GADD45B.

Methods Skin fibroblasts from patients affected by ALF secondary to NBAS deficiency were obtained. Fibroblasts were cultured for 24 hours before stress was applied by increasing their incubation temperature to 40 °C for 24 hours or switching to a low glucose medium. To investigate for NMD disruption, RNA was extracted from fibroblasts and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed for GADD45A and GADD45B, the expressions of which increase when NMD is disrupted.

Results The variants observed in the 4 patients affected by NBAS deficiency is represented in table 1. As expected, cell viability increased in all cell lines incubated at 37 °C with a glucose concentration of 4.5g/L in the culture medium. When the incubation temperature was increased to 40 °C, patient cells demonstrated a lower cell viability in comparison to controls at 500 cells/well. Under glucose deprivation, cell growth was hampered for NBAS3 but was maintained in all other cells at 48 and 72 hours.

For the evaluation of NMD, the expression of GADD45A and GADD45B were higher in control cells in comparison to affected patients.

Conclusion This work expands on the currently limited understanding of the pathobiology of NBAS deficiency. The application of stress on cultured fibroblasts from affected patients demonstrated some impairment in viability in comparison to healthy controls but this finding was not entirely consistent. The expression of endogenous NMD targets, GADD45A and GADD45B, were lower in patient cells suggesting that NMD was maintained.