Novel mutation in the adiponectin (ADIPOQ) gene is associated with hypoadiponectinaemia in Japanese-Brazilians

P>Objective Adiponectin is an important mediator of insulin sensitivity, encoded by the ADIPOQ gene. Here we describe two Japanese-Brazilian families with hypoadiponectinaemia due to a novel mutation in ADIPOQ. Design and patients In this study, we examined the entire translated regions of adiponectin in Japanese-Brazilians, a population with one of the highest prevalence rates of diabetes worldwide. We screened 200 patients with type 2 diabetes (DM) and 240 age-matched subjects with normal glucose tolerance. Results A novel heterozygous T deletion at position 186 in exon 2 of ADIPOQ, causing a frameshift at codon 62 and leading to a premature termination at codon 168 (p.Gly63ValfsX106), was found in two individuals with diabetes. This mutation was not found in 240 nondiabetic control subjects. In addition, we screened the mutation in an expanded set of 100 nondiabetic subjects from the general Brazilian population, but we found no mutations. In addition, six family members of the probands were identified as mutation-carriers. Individuals who were mutation-carriers had markedly low plasma adiponectin concentrations compared with those without the mutation [DM: 0 center dot 65 (0 center dot 59-1 center dot 34) mu g/ml vs. 5 center dot 30 (3 center dot 10-8 center dot 55) mu g/ml, P < 0 center dot 0001; normal glucose tolerance: 0 center dot 95 (0 center dot 76-1 center dot 48) mu g/ml vs. 8 center dot 50 (5 center dot 52-14 center dot 55) mu g/ml, P = 0 center dot 003]. All individuals carrying the p.Gly63ValfsX106 mutation and older than 30 years were found to be diabetic. Conclusions We describe for the first time a frameshift mutation in exon 2 of the ADIPOQ gene, which modulates adiponectin levels and may contribute to the genetic risk of late-onset diabetes in Japanese-Brazilians.

Functional analysis of a novel missense NBC1 mutation and of other mutations causing proximal renal tubular acidosis

Mutations in the Na+-HCO3- cotransporter NBC1 cause severe proximal tubular acidosis (pRTA) associated with ocular abnormalities. Recent studies have suggested that at least some NBC1 mutants show abnormal trafficking in the polarized cells. This study identified a new homozygous NBC1 mutation (G486R) in a patient with severe pRTA. Functional analysis in Xenopus oocytes failed to detect the G486R activity due to poor surface expression. In ECV304 cells, however, G486R showed the efficient membrane expression, and its transport activity corresponded to approximately 50% of wild-type (WT) activity. In Madin-Darby canine kidney (MDCK) cells, G486R was predominantly expressed in the basolateral membrane domain as observed for WT. Among the previously identified NBC1 mutants that showed poor surface expression in oocytes, T485S showed the predominant basolateral expression in MDCK cells. On the other hand, L522P was exclusively retained in the cytoplasm in ECV304 and MDCK cells, and functional analysis in ECV304 cells failed to detect its transport activity. These results indicate that G486R, like T485S, is a partial loss of function mutation without major trafficking abnormalities, while L522P causes the clinical phenotypes mainly through its inability to reach the plasma membranes. Multiple experimental approaches would be required to elucidate potential disease mechanism by NBC1 mutations.

Variable phenotypic manifestations of a K44N mutation in the TGIF gene

The etiologies and clinical spectra of HPE are extremely heterogeneous. Here, we report a Brazilian boy with lobar holoprosencephaly who was ascertained in a sample of 60 patients with HPE and HPE-like phenotypes and screened for molecular analysis of the major HPE causative genes: SHH, PTCH, SIX3, GLI2, and TGIF This boy presented a p.K44N (c.132G > T) mutation in exon 2 of the TGIF gene which was inherited from his phenotypically normal mother. This mutation leads to lysine to arginine amino acid change and is predicted to be a damaging mutation. Clinical aspects involving variable phenotypical manifestations in different mutations of TGIF are discussed. (c) 2007 Elsevier B.V. All rights reserved.

Carpenter Syndrome: Extended RAB23 Mutation Spectrum and Analysis of Nonsense-mediated mRNA Decay

Carpenter syndrome, a rare autosomal recessive disorder characterized by a combination of craniosynostosis, polysyndactyly, obesity, and other congenital malformations, is caused by mutations in RAB23, encoding a member of the Rab-family of small GTPases. In 15 out of 16 families previously reported, the disease was caused by homozygosity for truncating mutations, and currently only a single missense mutation has been identified in a compound heterozygote. Here, we describe a further 8 independent families comprising 10 affected individuals with Carpenter syndrome, who were positive for mutations in RAB23. We report the first homozygous missense mutation and in-frame deletion, highlighting key residues for RAB23 function, as well as the first splice-site mutation. Multi-suture craniosynostosis and polysyndactyly have been present in all patients described to date, and abnormal external genitalia have been universal in boys. High birth weight was not evident in the current group of patients, but further evidence for laterality defects is reported. No genotype-phenotype correlations are apparent. We provide experimental evidence that transcripts encoding truncating mutations are subject to nonsense-mediated decay, and that this plays an important role in the pathogenesis of many RAB23 mutations. These observations refine the phenotypic spectrum of Carpenter syndrome and offer new insights into molecular pathogenesis. (C) 2011 Wiley-Liss, Inc.

Iodide Transport Defect: Functional Characterization of a Novel Mutation in the Na(+)/I(-) Symporter 5 `-Untranslated Region in a Patient with Congenital Hypothyroidism

Context: Iodide transport defect (ITD) is an autosomal recessive disorder caused by impaired Na(+)/I(-) symporter (NIS)-mediated active iodide accumulation into thyroid follicular cells. Clinical manifestations comprise a variable degree of congenital hypothyroidism and goiter, and low to absent radioiodide uptake, as determined by thyroid scintigraphy. Hereditary molecular defects in NIS have been shown to cause ITD. Objective: Our objective was to perform molecular studies on NIS in a patient with congenital hypothyroidism presenting a clinical ITD phenotype. Design: The genomic DNA encoding NIS was sequenced, and an in vitro functional study of a newly identified NIS mutation was performed. Results: The analysis revealed the presence of an undescribed homozygous C to T transition at nucleotide -54 (-54C>T) located in the 5`-untranslated region in the NIS sequence. Functional studies in vitro demonstrated that the mutation was associated with a substantial decrease in iodide uptake when transfected into Cos-7 cells. The mutation severely impaired NIS protein expression, although NIS mRNA levels remained similar to those in cells transfected with wild-type NIS, suggesting a translational deficiency elicited by the mutation. Polysome profile analysis demonstrated reduced levels of polyribosomes-associated mutant NIS mRNA, consistent with reduced translation efficiency. Conclusions: We described a novel mutation in the 5`-untranslated region of the NIS gene in a newborn with congenital hypothyroidism bearing a clinical ITD phenotype. Functional evaluation of the molecular mechanism responsible for impaired NIS-mediated iodide concentration in thyroid cells indicated that the identified mutation reduces NIS translation efficiency with a subsequent decrease in protein expression and function. (J Clin Endocrinol Metab 96: E1100-E1107, 2011)

A Single Mutation at the Sheet Switch Region Results in Conformational Changes Favoring lambda 6 Light-Chain Fibrillogenesis

Systemic amyloid light-chain (LC) amyloidosis is a disease process characterized by the pathological deposition of monoclonal LCs in tissue. All LC subtypes are capable of fibril formation although lambda chains, particularly those belonging to the lambda 6 type, are overrepresented. Here, we report the thermodynamic and in vitro fibrillogenic properties of several mutants of the lambda 6 protein 6aJL2 in which Pro7 and/or His8 was substituted by Ser or Pro. The H8P and H8S mutants were almost as stable as the wildtype protein and were poorly fibrillogenic. In contrast, the P7S mutation decreased the thermodynamic stability of 6aJL2 and greatly enhanced its capacity to form amyloid-like fibrils in vitro. The crystal structure of the P7S mutant showed that the substitution induced both local and long-distance effects, such as the rearrangement of the V(L) (variable region of the light chain)-V(L) interface. This mutant crystallized in two orthorhombic polymorphs, P2(1)2(1)2(1) and C222(1). In the latter, a monomer that was not arranged in the typical Bence-Jones dimer was observed for the first time. Crystal-packing analysis of the C222(1) lattice showed the establishment of intermolecular beta-beta interactions that involved the N-terminus and beta-strand B and that these could be relevant in the mechanism of LC fibril formation. Our results strongly suggest that Pro7 is a key residue in the conformation of the N-terminal sheet switch motif and, through long-distance interactions, is also critically involved in the contacts that stabilized the V(L) interface in lambda 6 LCs. (C) 2009 Elsevier Ltd. All rights reserved.