Novel exon 12 mutations in the HIF2A gene associated with erythrocytosis.

Erythrocytosis can arise from deregulation of the erythropoietin (Epo) axis resulting from defects in the oxygen-sensing pathway. Epo synthesis is controlled by the hypoxia inducible factor (HIF) complex, composed of an a and a ß subunit. There are 2 main a subunits, HIF-1a and HIF-2a. Recently, a HIF-2a Gly537Trp mutation was identified in a family with erythrocytosis. This raises the possibility of HIF2A mutations being associated with other cases of erythrocytosis. We now report a subsequent analysis of HIF2A in a cohort of 75 erythrocytosis patients and identify 4 additional patients with novel heterozygous Met535Val and Gly537Arg mutations. All patients presented at a young age with elevated serum Epo. Mutations at Gly-537 account for 4 of 5 HIF2A mutations associated with erythrocytosis. These findings support the importance of HIF-2a in human Epo regulation and warrant investigation of HIF2A in patients with unexplained erythrocytosis.

Identification of novel Factor XI mutations in a patient requiring dental extractions

Factor XI is a serine protease that participates in the intrinsic pathway of blood coagulation. Patients deficient in factor XI exhibit varying degrees of post operative bleeding following invasive surgical procedures such as dental extractions. Objectives: The aim of the study was to identify the specific mutations in a patient from a family with known factor XI deficiency. Methods: Samples were obtained from the patient, his mother and his father and subjected to DNA sequencing. Each protein coding exon 2-15 of the factor XI gene was amplified by polymerase chain reaction (PCR) followed by bidirectional sequencing utilizing di-deoxy chain termination chemistry. Results: The patient had a factor XI level of 20% of normal. Initial sequencing of factor XI from the patient identified a point mutation (646G>A) and a putative splice site mutation (1567+4A>T) in intron 13. These are novel previously unreported mutations. DNA sequence analysis of the mother revealed the 1567+4A>T mutation and the father exhibited the 646G>A mutation. As a consequence the treatment proceeded without serious bleeding complication and required administration only of transexamic acid though factor XI was available as haemostatic cover. Conclusion: The two mutations identified in this family are novel; further laboratory investigation of the functional consequences of those mutations is currently underway. Although factor XI deficiency is rare in the Northern Irish population this study highlights the techniques available to sequence and analyse this and similar haematological disorders.

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.

Role of the Mitochondrial Mutations, m. 827A > G and the Novel m. 7462C > T, in the Origin of Hearing Loss

Samples from 30 deaf probands exhibiting features suggestive of syndromic mitochondrial deafness or from families with maternal transmission of deafness were selected for investigation of mutations in the mitochondrial genes MT-RNR1 and MT-TS1. Patients with mutation m. 1555A>G had been previously excluded from this sample. In the MT-RNR1 gene, five probands presented the m. 827A>G sequence variant, of uncertain pathogenicity. This change was also detected in 66 subjects of an unaffected control sample of 306 Brazilian individuals from various ethnic backgrounds. Given its high frequency, we consider it unlikely to have a pathogenic role on hereditary deafness. As to the MT-TS1 gene, one proband presented the previously known pathogenic m. 7472insC mutation and three probands presented a novel variant, m. 7462C>T, which was absent from the same control sample of 306 individuals. Because of its absence in control samples and association with a family history of hearing impairment, we suggest it might be a novel pathogenic mutation.

Novel OTOF mutations in Brazilian patients with auditory neuropathy

The OTOF gene encoding otoferlin is associated with auditory neuropathy (AN), a type of non-syndromic deafness. We investigated the contribution of OTOF mutations to AN and to non-syndromic recessive deafness in Brazil. A test for the Q829X mutation was carried out on a sample of 342 unrelated individuals with non-syndromic hearing loss, but none presented this mutation. We selected 48 cases suggestive of autosomal recessive inheritance, plus four familial and seven isolated cases of AN, for genotyping of five microsatellite markers linked to the OTOF gene. The haplotype analysis showed compatibility with linkage in 11 families (including the four families with AN). Samples of the 11 probands from these families and from seven isolated cases of AN were selected for an exon-by-exon screening for mutations in the OTOF gene. Ten different pathogenic variants were detected, among which six are novel. Among the 52 pedigrees with autosomal recessive inheritance (including four familial cases of AN), mutations were identified in 4 (7.7%). Among the 11 probands with AN, seven had at least one pathogenic mutation in the OTOF gene. Mutations in the OTOF gene are frequent causes of AN in Brazil and our results confirm that they are spread worldwide. Journal of Human Genetics (2009) 54, 382-385; doi: 10.1038/jhg.2009.45; published online 22 May 2009

Identification of 2 Novel ANTXR2 Mutations in Patients With Hyaline Fibromatosis Syndrome and Proposal of a Modified Grading System

Juvenile hyaline fibromatosis (JHF) and infantile systemic hyalinosis (ISH) are rare, autosomal recessive disorders of the connective tissue caused by mutations in the gene encoding the anthrax toxin receptor 2 protein (ANTXR2) located on chromosome 4q21. Characteristically, these conditions present with overlapping clinical features, such as nodules and/or pearly papules, gingival hyperplasia, flexion contractures of the joints, and osteolytic bone defects. The present report describes a pair of sibs and three other JHF/ISH patients whose diagnoses were based on typical clinical manifestations and confirmed by histopathologic analyses and/or molecular analysis. A comparison of ISH and JHF, additional thoughts about new terminology (hyaline fibromatosis syndrome) and a modified grading system are also included. (C) 2012 Wiley Periodicals, Inc.

Identification of eight novel coagulation factor XIII subunit A mutations: implied consequences for structure and function

Severe hereditary coagulation factor XIII deficiency is a rare homozygous bleeding disorder affecting one person in every two million individuals. In contrast, heterozygous factor XIII deficiency is more common, but usually not associated with severe hemorrhage such as intracranial bleeding or hemarthrosis. In most cases, the disease is caused by F13A gene mutations. Causative mutations associated with the F13B gene are rarer.

Characterization of novel StAR (steroidogenic acute regulatory protein) mutations causing non-classic lipoid adrenal hyperplasia

Context Steroidogenic acute regulatory protein (StAR) is crucial for transport of cholesterol to mitochondria where biosynthesis of steroids is initiated. Loss of StAR function causes lipoid congenital adrenal hyperplasia (LCAH). Objective StAR gene mutations causing partial loss of function manifest atypical and may be mistaken as familial glucocorticoid deficiency. Only a few mutations have been reported. Design To report clinical, biochemical, genetic, protein structure and functional data on two novel StAR mutations, and to compare them with published literature. Setting Collaboration between the University Children's Hospital Bern, Switzerland, and the CIBERER, Hospital Vall d'Hebron, Autonomous University, Barcelona, Spain. Patients Two subjects of a non-consanguineous Caucasian family were studied. The 46,XX phenotypic normal female was diagnosed with adrenal insufficiency at the age of 10 months, had normal pubertal development and still has no signs of hypergonodatropic hypogonadism at 32 years of age. Her 46,XY brother was born with normal male external genitalia and was diagnosed with adrenal insufficiency at 14 months. Puberty was normal and no signs of hypergonadotropic hypogonadism are present at 29 years of age. Results StAR gene analysis revealed two novel compound heterozygote mutations T44HfsX3 and G221S. T44HfsX3 is a loss-of-function StAR mutation. G221S retains partial activity (~30%) and is therefore responsible for a milder, non-classic phenotype. G221S is located in the cholesterol binding pocket and seems to alter binding/release of cholesterol. Conclusions StAR mutations located in the cholesterol binding pocket (V187M, R188C, R192C, G221D/S) seem to cause non-classic lipoid CAH. Accuracy of genotype-phenotype prediction by in vitro testing may vary with the assays employed.

Novel ADAMTS13 mutations in an obstetric patient with upshaw-schulman syndrome

Upshaw-Schulman syndrome (USS) is a rarely reported congenital form of thrombotic thrombocytopenic purpura (TTP) that results from mutations in the ADAMTS13 gene. Many USS patients are diagnosed during the second or third trimester of their first pregnancy. We present a patient diagnosed with USS following retinal detachments and intrauterine fetal demise at 34 weeks of gestation. The patient's plasma was tested for ADAMTS13 activity, inhibitor, and antibody. Subsequently, she and her first-degree relatives had ADAMTS13 gene sequencing. Initially, the patient was found to have an ADAMTS13 activity of <5% in the absence of an ADAMTS13 inhibitor (FRETS assay) or antibody (immunoassay). Repeat studies in the months following hospital discharge showed persistent, undetectable ADAMTS13 activity and she was given a clinical diagnosis of USS. Molecular sequencing demonstrated two novel missense mutations in the ADAMTS13 gene: one in the maternal exon 17 (p.Ala690Thr due to nucleotide substitution c.2068 G>A) and another in the paternal exon 22 (p.Arg915Cys due to nucleotide substitution c.2746 C>T). In addition to being compound heterozygous for two ADAMTS13 mutations, the patient also had two maternally inherited single nucleotide polymorphisms: p.P618A (exon 16) and p.A732V (exon 18). Her parents and only sister had normal or near-normal ADAMTS13 activity. Each was heterozygous for one of the novel missense mutations. This case highlights the importance of molecular analysis of the ADAMTS13 gene in patients and family members when the severe ADAMTS13 deficiency does not appear to be autoimmune in nature. J. Clin. Apheresis, 2012. © 2012 Wiley Periodicals, Inc.

Identification and in silico analyses of novel TGFBR1 and TGFBR2 mutations in Marfan syndrome-related disorders

Very recently, heterozygous mutations in the genes encoding transforming growth factor beta receptors I (TGFBR1) and II (TGFBR2) have been reported in Loeys-Dietz aortic aneurysm syndrome (LDS). In addition, dominant TGFBR2 mutations have been identified in Marfan syndrome type 2 (MFS2) and familial thoracic aortic aneurysms and dissections (TAAD). In the past, mutations of these genes were associated with atherosclerosis and several human cancers. Here, we report a total of nine novel and one known heterozygous sequence variants in the TGFBR1 and TGFBR2 genes in nine of 70 unrelated individuals with MFS-like phenotypes who previously tested negative for mutations in the gene encoding the extracellular matrix protein fibrillin-1 (FBN1). To assess the pathogenic impact of these sequence variants, in silico analyses were performed by the PolyPhen, SIFT, and Fold-X algorithms and by means of a 3D homology model of the TGFBR2 kinase domain. Our results showed that in all but one of the patients the pathogenic effect of at least one sequence variant is highly probable (c.722C > T, c.799A > C, and c.1460G > A in TGFBR1 and c.773T > G, c.1106G > T, c.1159G > A, c.1181G > A, and c.1561T > C in TGFBR2). These deleterious alleles occurred de novo or segregated with the disease in the families, indicating a causative association between the sequence variants and clinical phenotypes. Since TGFBR2 mutations found in patients with MFS-related disorders cannot be distinguished from heterozygous TGFBR2 mutations reported in tumor samples, we emphasize the importance of segregation analysis in affected families. In order to be able to find the mutation that is indeed responsible for a MFS-related phenotype, we also propose that genetic testing for sequence alterations in TGFBR1 and TGFBR2 should be complemented by mutation screening of the FBN1 gene.

Novel chloride channel mutations leading to mild myotonia among Chinese

We describe two Chinese families with a mild form of the myotonia congenita due to novel chloride channel (ClCN1) mutations. In one case, heterozygous I553F and H555N mutations were found. The patient shared the I553F mutation with his healthy father, and his mother had a history of mild myotonia when she was younger. In another family, autosomal dominant myotonia congenita was due to a L844F change. The physiological effects of the mutations were examined by using the two-electrode voltage-clamp technique after expression of the channels in Xenopus oocytes. All mutations drastically shifted the voltage required for half-maximal activation, more under conditions mimicking the homozygous situation, than under conditions mimicking the heterozygous situation. The larger effect was seen in the compound heterozygous situation combining the I553F and the H555N mutations. Our data suggest that myotonia congenita caused by CLCN1 mutations in Chinese have similar variable features to those found in the West.