ABCC9-related Intellectual disability Myopathy Syndrome is a KATP channelopathy with loss-of-function mutations in ABCC9.

Mutations in genes encoding K_ATP channel subunits have been reported for pancreatic disorders and Cantú syndrome. Here, we report a syndrome in six patients from two families with a consistent phenotype of mild intellectual disability, similar facies, myopathy, and cerebral white matter hyperintensities, with cardiac systolic dysfunction present in the two oldest patients. Patients are homozygous for a splice-site mutation in ABCC9 (c.1320 + 1 G > A), which encodes the sulfonylurea receptor 2 (SUR2) subunit of K_ATP channels. This mutation results in an in-frame deletion of exon 8, which results in non-functional K_ATP channels in recombinant assays. SUR2 loss-of-function causes fatigability and cardiac dysfunction in mice, and reduced activity, cardiac dysfunction and ventricular enlargement in zebrafish. We term this channelopathy resulting from loss-of-function of SUR2-containing K_ATP channels ABCC9-related Intellectual disability Myopathy Syndrome (AIMS). The phenotype differs from Cantú syndrome, which is caused by gain-of-function ABCC9 mutations, reflecting the opposing consequences of K_ATP loss- versus gain-of-function. ABCC9 encodes the SUR2 subunit of K_ATP channels and dominant genetic variants in ABCC9 have been associated with cardiac phenotypes. Here, the authors report recessive ABCC9 mutations in individuals with mild intellectual disability, myopathy and cardiac systolic dysfunction which is associated with loss of K_ATP channel function. [ABSTRACT FROM AUTHOR]