The C42R mutation in the Kir6.2 (KCNJ11) gene as a cause of transient neonatal diabetes, childhood diabetes, or later-onset, apparently type 2 diabetes mellitus.
BACKGROUND
Known genes in maturity-onset diabetes of the young account for only a fraction of families with dominantly inherited diabetes in Japan. There should be as-yet-unidentified genes that account for the rest of the patients.


OBJECTIVE
To identify and characterize the mutation responsible for a Japanese family with dominantly inherited diabetes mellitus.


METHODS
Members of a four-generation family with dominantly inherited diabetes mellitus observed in three generations. None of the patients in this family had permanent neonatal diabetes. One had transient neonatal diabetes, one had childhood diabetes, and the others had adult-onset diabetes without autoantibodies or insulin resistance.


METHODS
Screening of the chromosomal location of the gene by a genome-wide linkage analysis followed by candidate gene sequencing. Confirmation of the functional significance of the identified mutation by the population survey and the physiological analysis.


RESULTS
We identified a novel mutation (C42R) in the KCNJ11 gene coding for the Kir6.2 subunit of the pancreatic ATP-sensitive potassium channel. The patch-clamp experiments using the mutated KCNJ11 showed that the mutation causes increased spontaneous open probability and reduced ATP sensitivity. The effect, however, was partially compensated by the reduction of functional ATP-sensitive potassium channel expression at the cell surface, which could account for the milder phenotype of our patients.


CONCLUSIONS
These results broaden the spectrum of diabetes phenotypes caused by mutations of KCNJ11 and suggest that mutations in this gene should be taken into consideration for not only permanent neonatal diabetes but also other forms of diabetes with milder phenotypes and later onset.
Yorifuji
Tohru
T
Department of Pediatrics, Kyoto University Hospital, 54 Shogoin Sakyo, Kyoto 606-8507, Japan. yorif@kuhp.kyoto-u.ac.jp
Nagashima
Kazuaki
K
Kurokawa
Keiji
K
Kawai
Masahiko
M
Oishi
Mariko
M
Akazawa
Yoshiharu
Y
Hosokawa
Masaya
M
Yamada
Yuichiro
Y
Inagaki
Nobuya
N
Nakahata
Tatsutoshi
T
D019943:Amino Acid Substitution; D001483:Base Sequence; D004247:DNA / Q000097:blood / Q000235:genetics / Q000302:isolation & purification; D017931:DNA Primers; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics*; D004553:Electric Conductivity; D005260:Female; D005799:Genes, Dominant; D006801:Humans; D007231:Infant, Newborn; D015640:Ion Channel Gating / Q000502:physiology; D008297:Male; D020125:Mutation, Missense; D010375:Pedigree; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics* / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D000099161:Kcnj11 Channel
D004247:DNA; D017931:DNA Primers; D024661:Potassium Channels, Inwardly Rectifying; D000099161:Kcnj11 Channel