Smg8 is a regulatory subunit involved in nonsense-mediated mRNA decay (NMD), a crucial cellular pathway that regulates mRNA transcription, transcript stability, and degrades transcripts with premature stop codons [4]. It binds to SMG9 and SMG1 to form the SMG1C complex and inhibits the kinase activity of SMG1 [4]. NMD is essential for mammalian embryonic development, brain development, and modulation of the stress response [1].

In humans, recessive, deleterious variants in SMG8 lead to a novel neurodevelopmental disorder with dysmorphic facies and cataracts, now defined as Alzahrani-Kuwahara syndrome (ALKUS) [3,4,5]. Patients with SMG8-related ALKUS show severe global developmental delay, microcephaly, facial dysmorphism, and variable congenital heart and eye malformations [3,4,5]. RNA-seq analysis of patients with SMG8 deficiency reveals a general increase in mRNA expression levels with significant overrepresentation of core NMD substrates, along with increased phosphorylation of UPF1, likely due to loss of SMG8-mediated inhibition of SMG1 kinase activity [3]. Loss-of-function mutations in either SMG8 or SMG9 in gastric cancer models cause ATR inhibitor resistance through an SMG1-mediated mechanism [2].

In conclusion, Smg8 plays a vital role in the NMD pathway, and its deficiency leads to overlapping developmental disorders likely due to impaired NMD. The study of Smg8-related loss-of-function models, especially in the context of ALKUS and gastric cancer, provides insights into the mechanisms underlying these diseases, which may aid in the development of novel therapeutic strategies.