Functional and pathogenic insights into CNNM4 variants in Jalili syndrome

Jalili syndrome, an autosomal recessive disorder causing cone-rod dystrophy and amelogenesis imperfecta, is a rare genetic disorder impacting visual and dental development. Missense variants (c.1474G > T and c.1475G > A) previously identified in patients with Jalili syndrome have been linked to functional impairment of CNNM4, however, the biological consequences of these pathogenic variants remain largely unexplored. In this study, we investigated the functional implications of these CNNM4 missense variants, which correspond to p.(Gly492Cys) and p.(Gly492Asp) substitutions within the CBS domain of the CNNM4 protein. Our findings demonstrated that these variants exhibit significantly reduced protein stability and increased mRNA decay rates compared with wild type. Despite exhibiting normal Mg²⁺ localization, the mutant proteins demonstrated significantly reduced Mg²⁺ extrusion activity. This suggests that the pathogenic mechanism underlying Jalili syndrome associated with these variants likely involves decreased mRNA and/or protein stability, rather than mislocalization. Our study provides valuable insights into the interplay between genetic variations, molecular stability, and functional consequences in the context of CNNM4-related disorders, highlighting the importance of CNNM4-mediated Mg²⁺ transport in Jalili syndrome. Further investigation into the mechanisms regulating CNNM4 expression and protein stability may reveal potential therapeutic avenues.