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.

CONTEXT: 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. SUBJECTS: 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.

Neonatal diabetes mellitus and neonatal polycystic, dysplastic kidneys: Phenotypically discordant recurrence of a mutation in the hepatocyte nuclear factor-1beta gene due to germline mosaicism.

Mutations in the gene coding for hepatocyte nuclear factor-1beta (HNF-1beta) have been known to cause a form of maturity-onset diabetes of the young (MODY5), which is usually characterized by dominantly inherited adolescence-onset diabetes mellitus associated with renal cysts. This report, however, describes recurrence of a novel missense mutation in the HNF-1beta gene, S148W (C443G), in two sibs, one with neonatal diabetes mellitus and the other with neonatal polycystic, dysplastic kidneys leading to early renal failure. The former patient had only a few small renal cysts with normal renal functions, and the latter had only a transient episode of hyperglycemia, which resolved spontaneously. Interestingly, both parents were clinically unaffected, and PCR restriction fragment length polymorphism analysis showed that the mother was a low-level mosaic of normal and mutant HNF-1beta, which suggested that the recurrence was caused by germline mosaicism. This is the first report of permanent neonatal diabetes mellitus caused by a mutation of the HNF-1beta gene as well as the first report of germline mosaicism of this gene. In addition, the two cases described here show that additional factors, genetic or environmental, can have a significant influence on the phenotypic expression of HNF-1beta mutations.

Fibrillin I gene polymorphism is associated with tall stature of normal individuals.

In order to test the hypothesis that polymorphisms of the Marfan syndrome gene (FBN1) might affect the stature (height) of normal individuals, we genotyped three exonic SNPs on 428 males, 219 with tall stature (>2 SD) and 209 with normal stature (within +/-1 SD). One of the SNPs, rs8033037, in exon 15 showed a significant correlation (P = 0.0061) with the adult height, suggesting that FBN1 is one of the 'stature genes' of normal individuals.

Molecular and clinical analyses of Japanese patients with carbamoylphosphate synthetase 1 (CPS1) deficiency.

Carbamoylphosphate synthetase I deficiency (CPS1D) is a urea-cycle disorder characterized by episodes of life-threatening hyperammonemia. Correct diagnosis is crucial for patient management, but is difficult to make from clinical presentation and conventional laboratory tests alone. Enzymatic or genetic diagnoses have also been hampered by difficult access to the appropriate organ and the large size of the gene (38 exons). In this study, in order to address this diagnostic dilemma, we performed the largest mutational and clinical analyses of this disorder to date in Japan. Mutations in CPS1 were identified in 16 of 18 patients with a clinical diagnosis of CPS1D. In total, 25 different mutations were identified, of which 19 were novel. Interestingly, in contrast to previous reports suggesting an extremely diverse mutational spectrum, 31.8% of the mutations identified in Japanese were common to more than one family. We also identified two common polymorphisms that might be useful for simple linkage analysis in prenatal diagnosis. The accumulated clinical data will also help to reveal the clinical presentation of this rare disorder in Japan.

Prevalence of Mutations in the FGFR3 Gene in Individuals with Idiopathic Short Stature.

FGFR3 (fibroblast growth factor receptor 3) is a gene responsible for the most common form of osteodysplasia, achondroplasia, which results in extreme short stature. An allelic disorder, hypochondroplasia, however, presents with a much milder phenotype and is sometimes indistinguishable from idiopathic short stature. In this study, in order to test the possibility of the mildest end of hypochondroplasia being labeled as idiopathic short stature and the possibility of polymorphism of FGFR3 acting as one of the stature genes of normal individuals, we examined the prevalence of sequence alterations of the FGFR3 gene among individuals diagnosed clinically with idiopathic short stature. Sequencing analysis of all exons of the FGFR3 gene on 54 individuals with idiopathic short stature did not reveal any sequence variations related to the stature of the individuals. These results suggest that hidden hypochondroplasia among idiopathic short stature individuals is not a common occurrence and the contribution of polymorphism of the FGFR3 gene as a determinant of stature in normal individuals is small if any.

Effects of arginine treatment on nutrition, growth and urea cycle function in seven Japanese boys with late-onset ornithine transcarbamylase deficiency.

BACKGROUND: The aim of this study was to investigate the effects of arginine on nutrition, growth and urea cycle function in boys with late-onset ornithine transcarbamylase deficiency (OTCD). Seven Japanese boys with late-onset OTCD enrolled in this study resumed arginine treatment after the cessation of this therapy for a few years. Clinical presentations such as vomiting and unconsciousness, plasma amino acids and urinary orotate excretion were followed chronologically to evaluate urea cycle function and protein synthesis with and without this therapy. In addition to height and body weight, blood levels of proteins, lipids, growth hormone (GH), insulin-like growth factor-I (IGF-I) and IGF-binding protein -3 (IGFBP-3) were monitored. RESULTS: The frequency of hyperammonemic attacks and urinary orotate excretion decreased significantly following the resumption of arginine treatment. Despite showing no marked change in body weight, height increased gradually. Extremely low plasma arginine increased to normal levels, while plasma glutamine and alanine levels decreased considerably. Except for a slight increase in high-density lipoprotein cholesterol level, blood levels of markers for nutrition did not change. In contrast, low serum IGF-I and IGFBP-3 levels increased to age-matched control levels, and normal urinary GH secretion became greater than the level observed in the controls. CONCLUSION: Arginine treatment is able to reduces attacks of hyperammonemia in boys with late-onset OTCD and to increase their growth.

Unexpectedly high prevalence of the mild form of propionic acidemia in Japan: presence of a common mutation and possible clinical implications.

Propionic acidemia [MIM 606054] is a form of organic acidemia caused by genetic deficiency of propionyl-CoA carboxylase (PCC) and characterized by attacks of severe metabolic acidemia and hyperammonemia beginning in the neonatal period or in early infancy. There are, however, patients who have higher PCC activities and present later with unusual symptoms, such as mild mental retardation or extrapyramidal symptoms, sometimes even without metabolic acidosis. Through the neonatal screening of more than 130,000 Japanese newborns we detected a frequency of patients with propionic acidemia more than ten times higher than previously reported, most of them with milder phenotypes. The mutational spectrum was quite different from that of patients with the severe form and there was a common mutation (Y435C) in the beta subunit of the PCC gene (PCCB). Since patients with the mild form could present with unusual symptoms and therefore could easily remain unrecognized, it is important to identify those patients and clarify their natural history. Molecularly, one of the mutations (A1288C) caused an unusual pattern of multiple exon skipping and another unidentified mutation lead to the absence of mRNA. Taking into consideration previous findings regarding PCCB mutations, it appears that this gene is particularly prone to posttranscriptional modifications such as missense mediated exon skipping, mRNA decay, or rapid product degradation.