Regulation of human insulin, IGF-I, and multidrug resistance protein 2 promoter activity by hepatocyte nuclear factor (HNF)-1beta and HNF-1alpha and the abnormality of HNF-1beta mutants.

Mutations in hepatocyte nuclear factor-1beta (HNF-1beta) lead to type 5 maturity-onset diabetes of the young (MODY5). Moreover, mutations in the HNF-1beta gene might cause multiorgan abnormalities including renal diseases, genital malformations, and abnormal liver function. The objective of this study was to investigate the molecular mechanism of diabetes mellitus, intrauterine growth retardation, and cholestasis observed in MODY5 patients. We analyzed the transactivity of wild-type and three mutant HNF-1beta on native human insulin, IGF-I, and multidrug resistance protein 2 (MRP2) promoters in combination with HNF-1alpha, using a reporter-assay system in transiently transfected mammalian cells. In the human insulin gene promoter, we found that the cooperation of HNF-1alpha and HNF-1beta is prominent. Absence of this cooperation was observed in all of the HNF-1beta mutants. In the human IGF-I and MRP2 promoters, we found that the HNF-1beta His153Asn (H153N) mutant had a mutant-specific repressive effect on both HNF-1alpha and wild-type HNF-1beta transactivity. Absence of the cooperation of HNF-1beta mutants with HNF-1alpha in the human insulin gene promoter might be one cause of defective insulin secretion. The H153N mutant-specific repression of HNF-1alpha and HNF-1beta transactivity in human IGF-I and MRP2 promoters might explain the case-specific clinical features of growth retardation and cholestasis observed only in early infancy. We found differential property of HNF-1alpha/HNF-1beta activity and the effect of HNF-1beta mutants by the promoters. We consider that analyses of HNF-1beta mutants on the intended human native promoters in combination with HNF-1alpha may be useful in investigating the molecular mechanisms of the various features in MODY5.

A novel compound heterozygous mutation in the thyroglobulin gene resulting in congenital goitrous hypothyroidism with high serum triiodothyronine levels.

Thyroglobulin abnormality is a rare cause of congenital hypothyroidism and only a limited number of mutations in the thyroglobulin gene have been reported. We analyzed the thyroglobulin gene in a patient with congenital goitrous hypothyroidism. This girl was identified with hyperthyrotropinemia in a neonatal mass-screening test. The patient had goiter, and her body weight gain was poor. Distal femoral epiphysis was absent on roentgenography. Her serum thyroxine level was low; however, her triiodothyronine level was high. Autoantibodies against triiodothyronine, thyroid peroxidase, and thyroglobulin were all negative. Her serum thyroglobulin level was undetectable. The thyroglobulin gene from the genomic DNA of the patient was analyzed by direct sequencing. Two novel heterozygous missense mutations, Cys1897Tyr (exon 31) and Arg2336Gln (exon 40), were found in the patient. The former mutation was derived from her mother, suggesting a compound heterozygous state. Normal triiodothyronine and low thyroxine concentrations are often observed in patients with thyroglobulin gene mutations. We considered that some patients with thyroglobulin abnormality might have high triiodothyronine levels. In cases of congenital goitrous hypothyroidism with normal-to-high triiodothyronine levels and low serum thyroglobulin levels, thyroglobulin abnormality should be considered.

A compound heterozygous mutation in the BSND gene detected in Bartter syndrome type IV.

Bartter syndrome is a genetic disorder with hypokalemic metabolic alkalosis and is classified into five types. Type IV Bartter syndrome is a type of neonatal Bartter syndrome with sensorineural deafness and has been recently shown to be caused by mutations in the BSND gene. Owing to the rarity of this disease, only a limited number of mutations have been reported. We analyzed the BSND gene in a patient with type IV Bartter syndrome. The patient was delivered at 37 weeks, with normal body weight, and his neonatal course was uneventful. He was examined for developmental delay and polyuria at age 1 year 8 months and was found to have hypokalemia, metabolic alkalosis, hyperreninemic hyperaldosteronism, and sensorineural deafness. He developed end-stage renal failure at age 15 years, and renal transplantation was performed. We identified compound heterozygous mutations (Q32X and G47R) in the BSND gene. Each mutation was inherited from the parents. The Q32X mutation is a novel mutation and the first nonsense mutation identified in this gene. The mild perinatal clinical features of the patient were similar to those of a patient reported with a homozygous G47R mutation. However, the severity of renal failure suggested that factors other than this gene might affect the manifestation of renal abnormalities.

Functional characterization of LMX1B mutations associated with nail-patella syndrome.

Nail-patella syndrome (NPS) is an autosomal dominant disease characterized by dysplastic nails, absent or hypoplastic patellae, elbow dysplasia, and nephropathy. Recently, it was shown that NPS is the result of heterozygous mutations in the LIM-homeodomain gene, LMX1B. Subsequently, many mutations of the LMX1B gene have been reported in NPS patients. However, functional analyses of the mutant proteins have been performed in only a few mutations. Furthermore, the mechanisms of dominant inheritance in humans have not been established. In the present study, we analyzed the LMX1B gene in three Japanese patients with NPS and identified two novel mutations, 6 nucleotide deletion (Delta246N 247Q) and V242L. These two mutations are located in the homeodomain of LMX1B. Functional analyses of the LMX1B mutants revealed that these mutants had diminished transcriptional activity and had lost DNA binding ability. Furthermore, we demonstrated that each mutant did not manifest a dominant-negative effect on the transcriptional activity of wild-type LMX1B. These results suggested that NPS is caused by loss-of-function mutations of LMX1B, and haploinsufficiency of LMX1B should be the predominant pathogenesis of NPS in humans.

Novel compound heterozygous AIRE mutations in a Japanese patient with APECED.

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a rare autosomal recessive disorder defined by the presence of two of three conditions, namely, Addison's disease, hypoparathyroidism, and mucocutaneous candidiasis. APECED is caused by alteration in a single gene, named the autoimmune regulator (AIRE) gene. We report AIRE gene mutations in a Japanese female with APECED. The patient is a 22-year-old Japanese female who was diagnosed with Addison's disease, hypoparathyroidism, and mucocutaneous candidiasis at age 8 years. Sequence analysis of the AIRE gene revealed novel compound heterozygous mutations. One was 1471 delCinsTT in exon 11 (GenBank accession no. AB006682), which leads to a frameshift and premature truncation of a 502 amino acid protein. The other was a G-->A transition at IVS11+1. Her mother was heterozygous for 1471 delCinsTT and was normal homozygous for IVS11+1. We found novel compound heterozygous mutations in the AIRE gene of a Japanese female with APECED.

Aire downregulates multiple molecules that have contradicting immune-enhancing and immune-suppressive functions.

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a systemic disease with autoimmune characteristics caused by mutations in a single gene called AIRE. Although a defect in negative selection has been emphasized for the pathogenesis of the autoimmune symptoms on the basis of studies of Aire-targeted mice, the function of the gene in the peripheral immune system and the cause of immunodeficiency noted in the disease have not been clarified yet. In this study, we demonstrated using murine Aire transfectants that Aire downregulates IL-1 receptor antagonist (IL-1Ra), which is important for immune suppression, and major histocompatibility complex (MHC) class II molecules, which are critical for acquired immunity. It was surprising to learn that Aire, which has been supposed to positively regulate transcription, downregulates multiple molecules. This downregulation of IL-1Ra and MHC class II molecules seems to be caused by the competition for transcriptional coactivator, CREB-binding protein (CBP), and may explain part of the contradictory (i.e., both autoimmune and immunodeficient) nature of APECED.