IDENTIFICATION AND FUNCTIONAL-ANALYSIS OF SULFONYLUREA RECEPTOR-1 VARIANTS IN JAPANESE PATIENTS WITH NIDDM

The sulfonylurea receptor 1 (SUR1) is an essential regulatory subunit of the beta-cell ATP-sensitive K+ channel (K-ATP). The possible role o f SUR1 gene mutation(s) in the development of NIDDM remains controvers ial as both a positive association and negative linkage results have b een reported, Therefore, Re examined the SUR1 gene at the single nucle otide level with single strand conformation polymorphism analysis in 1 00 Japanese NIDDM patients, We identified a total of five amino acid s ubstitutions and 17 silent mutations by examining all 39 exons of this gene, Two rare novel mutations, (DN)-N-811 in exon 20 and (RC)-C-835 in exon 21, were identified in the first nucleotide-binding fold (NBF) , a functionally important region of SUR1, in one patient. each, both heterozygotes. To analyze possible functional alterations, we reconsti tuted the mutant K-ATP by coexpressing beta-cell inward rectifier (BIR ) (Kir 6.2), a channel subunit of K-ATP, mutant SUR1 in HEK293T and CO S-7 cells, As demonstrated by the patch clamp technique and rubidium ( Rb+) efflux studies, neither mutation alters the properties of channel activities. Two other rare missense mutations, R(275)Q in exon 6 and (VM)-M-560 in exon 12, were also identified, The R(275)Q substitution was not found in 67 control subjects, and (VM)-M-560 was present in th ree control subjects, Neither of these substitutions appeared to coseg regate with NIDDM in the probands' families, A previously reported S(1 370)A substitution located in the second NBF was also common in the Ja panese subjects (allelic frequency 0.37), and was found at an equal fr equency in nondiabetic control subjects, In conclusion, SUR1 mutations impairing K-ATP function do not appear to be major determinants of NI DDM susceptibility in Japanese.