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A Mutation in the TMD0-L0 Region of Sulfonylurea Receptor-1 (L225P) Causes Permanent Neonatal Diabetes Mellitus (PNDM)

¹ Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri
² Division of Endocrinology, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania

Address correspondence and reprint requests to Colin G. Nichols, Department of Cell Biology and Physiology, Washington University School of Medicine, 660 South Euclid Ave., St. Louis, MO 63110. E-mail: cnichols{at}wustl.edu

Abbreviations: ABC, ATP-binding cassette; K_ATP channel, ATP-sensitive K⁺ channel; NDM, neonatal diabetes mellitus; PNDM, permanenent neonatal diabetes mellitus; SUR, sulfonylurea receptor; TMD, transmembrane domain

OBJECTIVE—We sought to examine the molecular mechanisms underlying permanenent neonatal diabetes mellitus (PNDM) in a patient with a heterozygous de novo L225P mutation in the L0 region of the sulfonylurea receptor (SUR)1, the regulatory subunit of the pancreatic ATP-sensitive K⁺ channel (K_ATP channel).

RESEARCH DESIGN AND METHODS—The effects of L225P on the properties of recombinant K_ATP channels in transfected COS cells were assessed by patch-clamp experiments on excised membrane patches and by macroscopic Rb-flux experiments in intact cells.

RESULTS—L225P-containing K_ATP channels were significantly more active in the intact cell than in wild-type channels. In excised membrane patches, L225P increased channel sensitivity to stimulatory Mg nucleotides without altering intrinsic gating or channel inhibition by ATP in the absence of Mg²⁺. The effects of L225P were abolished by SUR1 mutations that prevent nucleotide hydrolysis at the nucleotide binding folds. L225P did not alter channel inhibition by sulfonylurea drugs, and, consistent with this, the patient responded to treatment with oral sulfonylureas.

CONCLUSIONS—L225P underlies K_ATP channel overactivity and PNDM by specifically increasing Mg-nucleotide stimulation of the channel, consistent with recent reports of mechanistically similar PNDM-causing mutations in SUR1. The mutation does not affect sulfonylurea sensitivity, and the patient is successfully treated with sulfonylureas.

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