Mechanistic basis of desmosome-targeted diseases

Desmosomes are dynamic junctions between cells that maintain the structural integrity of skin and heart tissues by withstanding shear forces. Mutations in component genes cause life-threatening conditions including arrhythmogenic right ventricular cardiomyopathy, and desmosomal proteins are targeted by pathogenic autoantibodies in skin blistering diseases such as pemphigus. Here, we review a set of newly discovered pathogenic alterations and discuss the structural repercussions of debilitating mutations on desmosomal proteins. The architectures of native desmosomal assemblies have been visualized by cryo-electron microscopy and cryo-electron tomography, and the network of protein domain interactions is becoming apparent. Plakophilin and desmoplakin mutations have been discovered to alter binding interfaces, structures, and stabilities of folded domains that have been resolved by X-ray crystallography and NMR spectroscopy. The flexibility within desmoplakin has been revealed by small-angle X-ray scattering and fluorescence assays, explaining how mechanical stresses are accommodated. These studies have shown that the structural and functional consequences of desmosomal mutations can now begin to be understood at multiple levels of spatial and temporal resolution. This review discusses the recent structural insights and raises the possibility of using modeling for mechanism-based diagnosis of how deleterious mutations alter the integrity of solid tissues

Pasireotide treatment for severe congenital hyper-insulinism due to a homozygous ABCC8 mutation

ABCC8 and KCJN11 mutations cause the most severe diazoxide-resistant forms of congenital hyperinsulinism (CHI). Somatostatin analogues are considered as secondline treatment in diazoxide-unresponsive cases. Current treatment protocols include the first-generation somatostatin analogue octreotide, although pasireotide, a second-generation somatostatin analogue, might be more effective in reducing insulin secretion. Herein we report the first off-label use of pasireotide in a boy with a severe therapy-resistant form of CHI due to a homozygous ABCC8 mutation. After partial pancreatectomy, hyperinsulinism persisted; in an attempt to prevent further surgery, off-label treatment with pasireotide was initiated. Short-acting pasireotide treatment caused high blood glucose level shortly after injection. Long-acting pasireotide treatment resulted in more stable glycemic control. No side effects (e.g., central adrenal insufficiency) were noticed during a 2-month treatment period. Because of recurrent hypoglycemia despite a rather high carbohydrate intake, the boy underwent near-total pancreatectomy at the age of 11 months. In conclusion, pasireotide treatment slightly improved glycemic control without side effects in a boy with severe CHI. However, the effect of pasireotide was not sufficient to prevent near-total pancreatectomy in this case of severe CHI

Mutations in IRS4 are associated with central hypothyroidism

Background: Four genetic causes of isolated congenital central hypothyroidism (CeH) have been identified, but many cases remain unexplained. We hypothesised the existence of other genetic causes of CeH with a Mendelian inheritance pattern. Methods: We performed exome sequencing in two families with unexplained isolated CeH and subsequently Sanger sequenced unrelated idiopathic CeH cases. We performed clinical and biochemical characterisation of the probands and carriers identified by family screening. We investigated IRS4 mRNA expression in human hypothalamus and pituitary tissue, and measured serum thyroid hormones and Trh and Tshb mRNA expression in hypothalamus and pituitary tissue of Irs4 knockout mice. Results: We found mutations in the insulin receptor substrate 4 (IRS4) gene in two pairs of brothers with CeH (one nonsense, one frameshift). Sequencing of IRS4 in 12 unrelated CeH cases negative for variants in known genes yielded three frameshift mutatio

Genome-wide association analyses identify new Brugada syndrome risk loci and highlight a new mechanism of sodium channel regulation in disease susceptibility.

Brugada syndrome (BrS) is a cardiac arrhythmia disorder associated with sudden death in young adults. With the exception of SCN5A, encoding the cardiac sodium channel Na1.5, susceptibility genes remain largely unknown. Here we performed a genome-wide association meta-analysis comprising 2,820 unrelated cases with BrS and 10,001 controls, and identified 21 association signals at 12 loci (10 new). Single nucleotide polymorphism (SNP)-heritability estimates indicate a strong polygenic influence. Polygenic risk score analyses based on the 21 susceptibility variants demonstrate varying cumulative contribution of common risk alleles among different patient subgroups, as well as genetic associations with cardiac electrical traits and disorders in the general population. The predominance of cardiac transcription factor loci indicates that transcriptional regulation is a key feature of BrS pathogenesis. Furthermore, functional studies conducted on MAPRE2, encoding the microtubule plus-end binding protein EB2, point to microtubule-related trafficking effects on Na1.5 expression as a new underlying molecular mechanism. Taken together, these findings broaden our understanding of the genetic architecture of BrS and provide new insights into its molecular underpinnings

Genetics and phenomics of hypothyroidism and goiter due to TPO mutations

Thyroid peroxidase (TPO) is a heme binding protein localized on the apical membrane of the thyrocyte. TPO enzymatic activity is essential for thyroid hormonogenesis. Inactivating mutations form the molecular basis for a specific subtype of congenital hypothyroidism: thyroid dyshormonogenesis due to an iodide organification defect. The most common phenotype of this autosomal recessive disease is a total iodide organification defect, with severe and permanent hypothyroidism as a consequence. Currently 61 properly annotated mutations in the TPO gene have been reported, of which the majority are missense mutations. Functional data of most missense mutations is not available, making it necessary to revert to in silico methods for functional interpretation of mutations. We hypothesize that iodine status is the main phenomic modifier of TPO function. (C) 2010 Elsevier Ireland Ltd. All rights reserve

The Fundamental Themes of Rural Planning

textabstractA 50-kb deletion was demonstrated in the gene encoding for the β-subunit of human hexosaminidase (HEXB), using field inversion gel electrophoresis (FIGE) of SfiI-digested chromosomal DNA from patients with Sandhoff disease. We investigated 14 patients from different parts of Europe and found no deletion in 5 patients, 2 patients homozygous for the deletion, and 7 patients with the deletion in one allele. The distribution of the 50-kb deletion was approximately in agreement with the Hardy-Weinberg equilibrium. The deletion was characterized using chromosomal DNA from one of the two homozygous patients. Restriction fragments were hybridized with a 1.6-kb (almost complete) and a 0.4-kb (5′) HEXB cDNA clone. It appeared that the deletion started in intron 5, extending in the 5′ direction and causing the loss of exon 1-5 and the promoter area of the HEXB gene

NKX2-1 mutations in brain-lung-thyroid syndrome: a case series of four patients

Brain-lung-thyroid syndrome (BLTS) characterized by congenital hypothyroidism, respiratory distress syndrome, and benign hereditary chorea is caused by thyroid transcription factor 1 (NKX2-1/TTF1) mutations. We report the clinical and molecular characteristics of four cases presenting with primary hypothyroidism, respiratory distress, and neurological disorder. Two of the four patients presenting with the triad of BLTS had NKX2-1 mutations, and one of these NKX2-1 [c.890_896del (p.Ala327Glyfs(star)52)] is a novel variant. The third patient without any identified NKX2-1 mutations was a carrier of mitochondrial mutation; this raises the possibility of mitochondrial mutations contributing to thyroid dysgenesis. Although rare, the triad of congenital hypothyroidism, neurological, and respiratory signs is highly suggestive of NKX2-1 anomalies. Screening for NKX2-1 mutations in patients with thyroid, lung, and neurological abnormalities will enable a unifying diagnosis and genetic counseling for the affected families. In addition, identification of an NKX2-1 defect would be helpful in allaying the concerns about inadequate thyroxine supplementation as the cause of neurological defects observed in some children with congenital hypothyroidis