A novel ABCC9 variant in a Greek family with Cantu syndrome affecting multiple generations highlights the functional role of the SUR2B NBD1.

Cantu syndrome (CS) (OMIM #239850) is an autosomal dominant multiorgan system condition, associated with a characteristic facial phenotype, hypertrichosis, and multiple cardiovascular complications. CS is caused by gain-of-function (GOF) variants in KCNJ8 or ABCC9 that encode pore-forming Kir6.1 and regulatory SUR2 subunits of ATP-sensitive potassium (KATP) channels. A novel heterozygous ABCC9 variant, c.2440G>T; p.Gly814Trp, was identified in three individuals from a four generation Greek family. The membrane potential in cells stably expressing hKir6.1 and hSUR2B with p.Gly814Trp was hyperpolarized compared to cells expressing WT channels, and inside-out patch-clamp assays of KATP channels formed with hSUR2B p.Gly814Trp demonstrated a decreased sensitivity to ATP inhibition, confirming a relatively mild GOF effect of this variant. The specific location of the variant reveals an unrecognized functional role of the first glycine in the signature motif of the nucleotide binding domains in ATP-binding cassette (ABC) protein ion channels.

Multiple Coronary Artery Microfistulas in a Girl with Kleefstra Syndrome.

Kleefstra syndrome is characterized by hypotonia, developmental delay, dysmorphic features, congenital heart defects, and so forth. It is caused by 9q34.3 microdeletions or EHMT1 mutations. Herein a 20-month-old girl with Kleefstra syndrome, due to a de novo subterminal deletion, is described. She exhibits a rare and complex cardiopathy, encompassing multiple coronary artery microfistulas, VSD/ASD, and PFO.