CRYBB1 mutation associated with congenital cataract and microcornea

The molecular characterization of a UK family with an autosomal dominant congenital cataract associated with microcornea is reported. METHODS: Family history and clinical data were recorded. This phenotype was linked to a 7.6 cM region of chromosome 22q11.2-q12.2, spanning the beta-crystallin gene cluster (ZMax of 3.91 for marker D22S1114 at theta=0). Candidate genes were PCR amplified and screened for mutations on both strands using direct sequencing. RESULTS: Sequencing of the coding regions and flanking intronic sequences of CRYBB2 and CRYBB1 showed the presence of a novel, heterozygous X253R change in exon 6 of CRYBB1. SSCP analysis confirmed that this sequence change segregated with the disease phenotype in all available family members and was not found in 109 ethnically matched controls. CONCLUSIONS: X253R is predicted to elongate the COOH-terminal extension of the protein and would be expected to disrupt beta-crystallin interactions. This is the first documented involvement of CRYBB1 in ocular development beyond cataractogenesis.

VAX1 mutation associated with microphthalmia, corpus callosum agenesis and orofacial clefting-the first description of a VAX1 phenotype in humans.

Vax1 and Vax2 have been implicated in eye development and the closure of the choroid fissure in mice and zebrafish. We sequenced the coding exons of VAX1 and VAX2 in 70 patients with anophthalmia/microphthalmia. In VAX1, we observed homozygosity for two successive nucleotide substitutions c.453G>A and c.454C>A, predicting p.Arg152Ser, in a proband of Egyptian origin with microphthalmia, small optic nerves, cleft lip/palate and corpus callosum agenesis. This mutation affects an invariant residue in the homeodomain of VAX1 and was absent from 96 Egyptian controls. It is likely that the mutation results in a loss of function, as the mutation results in a phenotype similar to the Vax1 homozygous null mouse. We did not identify any mutations in VAX2. This is the first description of a phenotype associated with a VAX1 mutation in humans and establishes VAX1 as a new causative gene for anophthalmia/microphthalmia. ©2011 Wiley Periodicals, Inc.

RET haplotype, not linked to the C620R activating mutation, associated with Hirschsprung disease in a novel MEN2 family

Hirschsprung disease is a congenital form of aganglionic megacolon that results from cristopathy. Hirschsprung disease usually occurs as a sporadic disease, although it may be associated with several inherited conditions, such as multiple endocrine neoplasia type 2. The rearranged during transfection (RET) proto-oncogene is the major susceptibility gene for Hirschsprung disease, and germline mutations in RET have been reported in up to 50% of the inherited forms of Hirschsprung disease and in 15-20% of sporadic cases of Hirschsprung disease. The prevalence of Hirschsprung disease in multiple endocrine neoplasia type 2 cases was recently determined to be 7.5% and the cooccurrence of Hirschsprung disease and multiple endocrine neoplasia type 2 has been reported in at least 22 families so far. It was initially thought that Hirschsprung disease could be due to disturbances in apoptosis or due to a tendency of the mutated RET receptor to be retained in the Golgi apparatus. Presently, there is strong evidence favoring the hypothesis that specific inactivating haplotypes play a key role in the fetal development of congenital megacolon/Hirschsprung disease. In the present study, we report the genetic findings in a novel family with multiple endocrine neoplasia type 2: a specific RET haplotype was documented in patients with Hirschsprung disease associated with medullary thyroid carcinoma, but it was absent in patients with only medullary thyroid carcinoma. Despite the limited number of cases, the present data favor the hypothesis that specific haplotypes not linked to RET germline mutations are the genetic causes of Hirschsprung disease.

Impairment of mitochondrial tRNAIle processing by a novel mutation associated with chronic progressive external ophthalmoplegia

We report a sporadic case of chronic progressive external ophthalmoplegia associated with ragged red fibers. The patient presented with enlarged mitochondria with deranged internal architecture and crystalline inclusions. Biochemical studies showed reduced activities of complex I, III and IV in skeletal muscle. Molecular genetic analysis of all mitochondrial tRNAs revealed a G to A transition at nt 4308; the G is a highly conserved nucleotide that participates in a GC base-pair in the T-stem of mammalian mitochondrial tRNA(Ile). The mutation was detected at a high level (approx. 50%) in muscle but not in blood. The mutation co-segregated with the phenotype, as the mutation was absent from blood and muscle in the patient's healthy mother. Functional characterization of the mutation revealed a six-fold reduced rate of tRNA(Ile) precursor 3' end maturation in vitro by tRNAse Z. Furthermore, the mutated tRNA(Ile) displays local structural differences from wild-type. These results suggest that structural perturbations reduce efficiency of tRNA(Ile) precursor 3' end processing and contribute to the molecular pathomechanism of this mutation.

Syntrophin mutation associated with long QT syndrome through activation of the nNOS-SCN5A macromolecular complex.

Mutations in 11 genes that encode ion channels or their associated proteins cause inherited long QT syndrome (LQTS) and account for approximately 75-80% of cases (LQT1-11). Direct sequencing of SNTA1, the gene encoding alpha1-syntrophin, was performed in a cohort of LQTS patients that were negative for mutations in the 11 known LQTS-susceptibility genes. A missense mutation (A390V-SNTA1) was found in a patient with recurrent syncope and markedly prolonged QT interval (QTc, 530 ms). SNTA1 links neuronal nitric oxide synthase (nNOS) to the nNOS inhibitor plasma membrane Ca-ATPase subtype 4b (PMCA4b); SNTA1 also is known to associate with the cardiac sodium channel SCN5A. By using a GST-fusion protein of the C terminus of SCN5A, we showed that WT-SNTA1 interacted with SCN5A, nNOS, and PMCA4b. In contrast, A390V-SNTA1 selectively disrupted association of PMCA4b with this complex and increased direct nitrosylation of SCN5A. A390V-SNTA1 expressed with SCN5A, nNOS, and PMCA4b in heterologous cells increased peak and late sodium current compared with WT-SNTA1, and the increase was partially inhibited by NOS blockers. Expression of A390V-SNTA1 in cardiac myocytes also increased late sodium current. We conclude that the A390V mutation disrupted binding with PMCA4b, released inhibition of nNOS, caused S-nitrosylation of SCN5A, and was associated with increased late sodium current, which is the characteristic biophysical dysfunction for sodium-channel-mediated LQTS (LQT3). These results establish an SNTA1-based nNOS complex attached to SCN5A as a key regulator of sodium current and suggest that SNTA1 be considered a rare LQTS-susceptibility gene.

Defective trafficking and function of KATP channels caused by a sulfonylurea receptor 1 mutation associated with persistent hyperinsulinemic hypoglycemia of infancy

The ATP-sensitive potassium channel (KATP) regulates insulin secretion in pancreatic β cells. Loss of functional KATP channels because of mutations in either the SUR1 or Kir6.2 channel subunit causes persistent hyperinsulinemic hypoglycemia of infancy (PHHI). We investigated the molecular mechanism by which a single phenylalanine deletion in SUR1 (ΔF1388) causes PHHI. Previous studies have shown that coexpression of ΔF1388 SUR1 with Kir6.2 results in no channel activity. We demonstrate here that the lack of functional expression is due to failure of the mutant channel to traffic to the cell surface. Trafficking of KATP channels requires that the endoplasmic reticulum-retention signal, RKR, present in both SUR1 and Kir6.2, be shielded during channel assembly. To ask whether ΔF1388 SUR1 forms functional channels with Kir6.2, we inactivated the RKR signal in ΔF1388 SUR1 by mutation to AAA (ΔF1388 SUR1AAA). Inactivation of similar endoplasmic reticulum-retention signals in the cystic fibrosis transmembrane conductance regulator has been shown to partially overcome the trafficking defect of a cystic fibrosis transmembrane conductance regulator mutation, ΔF508. We found that coexpression of ΔF1388 SUR1AAA with Kir6.2 led to partial surface expression of the mutant channel. Moreover, mutant channels were active. Compared with wild-type channels, the mutant channels have reduced ATP sensitivity and do not respond to stimulation by MgADP or diazoxide. The RKR → AAA mutation alone has no effect on channel properties. Our results establish defective trafficking of KATP channels as a molecular basis of PHHI and show that F1388 in SUR1 is critical for normal trafficking and function of KATP channels.

MEN1 Gene Mutation and Reduced Expression Are Associated With Poor Prognosis in Pulmonary Carcinoids

Context: MEN1 gene alterations have been implicated in lung carcinoids, but their effect on gene expression and disease outcome is unknown. Objective: Our objective was to analyze MEN1 gene and expression anomalies in lung neuroendocrine neoplasms and their correlations with clinicopathologic data and disease outcome. Design: We examined 74 lung neuroendocrine neoplasms including 58 carcinoids and 16 high-grade neuroendocrine carcinomas (HGNECs) for MEN1 mutations (n = 70) and allelic losses (n = 69), promoter hypermethylation (n = 65), and mRNA (n = 74) expression. Results were correlated with disease outcome. Results: MEN1 mutations were found in 7 of 55 (13%) carcinoids and in 1 HGNEC, mostly associated with loss of the second allele. MEN1 decreased expression levels correlated with the presence of mutations (P = .0060) and was also lower in HGNECs than carcinoids (P = .0024). MEN1 methylation was not associated with mRNA expression levels. Patients with carcinoids harboring MEN1 mutation and loss had shorter overall survival (P = .039 and P = .035, respectively) and low MEN1 mRNA levels correlated with distant metastasis (P = .00010) and shorter survival (P = .0071). In multivariate analysis, stage and MEN1 allelic loss were independent predictors of prognosis. Conclusion: Thirteen percent of pulmonary carcinoids harbor MEN1 mutation associated with reduced mRNA expression and poor prognosis. Also in mutation-negative tumors, low MEN1 gene expression correlates with an adverse disease outcome. Hypermethylation was excluded as the underlying mechanism.

A point mutation in the HIV-1 Tat responsive element is associated with postintegration latency.

Study of the mechanism of HIV-1 postintegration latency in the ACH2 cell line demonstrates that these cells failed to increase HIV-1 production following treatment with exogenous Tat. Reasoning that the defect in ACH2 cells involves the Tat response, we analyzed the sequence of tat cDNA and Tat responsive element (TAR) from the virus integrated in ACH2. Tat cDNA sequence is closely related to that of HIV LAI, and the encoded protein is fully functional in terms of long terminal repeat (LTR) transactivation. Cloning of a region corresponding to the 5'-LTR from ACH2, however, identified a point mutation (C37 -> T) in TAR. This mutation impaired Tat responsiveness of the LTR in transient transfection assays, and the measured defect was complemented in cells that had been treated with tetradecanoyl phorbol acetate or tumor necrosis factor type alpha (TNF-alpha). A compensatory mutation in TAR (G28 -> A), designed to reestablish base pairing in the TAR hairpin, restored wild-type Tat responsiveness. When the (C37 -> T) mutation was introduced in an infectious clone of HIV-1, no viral production was measured in the absence of TNF-alpha, whereas full complementation was observed when the infection was conducted in the presence of TNF-alpha or when a compensatory mutation (G28 -> A) was introduced into TAR. These experiments identify a novel mutation associated with HIV-1 latency and suggest that alterations in the Tat-TAR axis can be a crucial determinant of the latent phenotype in infected individuals.

Haplotype analysis suggest common founders in carriers of the recurrent BRCA2 mutation, 3398delAAAAG, in French Canadian hereditary breast and/ovarian cancer families

Affiliation: Faculté de médicine, Université de Montréal

A novel succinate dehydrogenase subunit B gene mutation, H132P, causes familial malignant sympathetic extraadrenal paragangliomas

We report a family with malignant sympathetic paragangliomas (PGL) exhibiting a new type of germline mutation in the succinate dehydrogenase subunit B (SDHB) gene. Two affected brothers, presenting with symptoms at the ages of 25 and 52 yr, suffered from malignant abdominal extraadrenal sympathetic PGL. They died of their disease at ages 43 and 61 yr. Their mother had the same history of signs and symptoms, suggesting a catecholamine-producing tumor at the age of 55 yr. Analysis of the germline DNA from these three patients revealed a novel mutation in exon 4 (H132P) of the SDHB gene. This mutation was absent in 160 control chromosomes. Loss of heterozygosity analysis of the tumors showed a loss of one SDHB allele, and RT-PCR-based expression analysis confirmed the exclusive expression of the mutated allele in both tumors. A review of the published PGL families revealed malignant tumors in seven of 12 well-documented families with SDHB mutation-associated extraadrenal PGL. These findings, as well as findings of the family reported here, suggest a strong causal relationship of SDHB germline mutations with malignant extraadrenal abdominal PGL and imply the necessity of a close follow-up of affected individuals and family members.

Clinical Application of Poly(ADP-Ribose) Polymerase Inhibitors in High-Grade Serous Ovarian Cancer

: High-grade serous ovarian cancer is characterized by genomic instability, with one half of all tumors displaying defects in the important DNA repair pathway of homologous recombination. Given the action of poly(ADP-ribose) polymerase (PARP) inhibitors in targeting tumors with deficiencies in this repair pathway by loss of BRCA1/2, ovarian tumors could be an attractive population for clinical application of this therapy. PARP inhibitors have moved into clinical practice in the past few years, with approval from the Food and Drug Administration (FDA) and European Medicines Agency (EMA) within the past 2 years. The U.S. FDA approval of olaparib applies to fourth line treatment in germline BRCA-mutant ovarian cancer, and European EMA approval to olaparib maintenance in both germline and somatic BRCA-mutant platinum-sensitive ovarian cancer. In order to widen the ovarian cancer patient population that would benefit from PARP inhibitors, predictive biomarkers based on a clear understanding of the mechanism of action are required. Additionally, a better understanding of the toxicity profile is needed if PARP inhibitors are to be used in the curative, rather than the palliative, setting. We reviewed the development of PARP inhibitors in phase I-III clinical trials, including combination trials of PARP inhibitors and chemotherapy/antiangiogenics, the approval for these agents, the mechanisms of resistance, and the outstanding issues, including the development of biomarkers and the rate of long-term hematologic toxicities with these agents.

IMPLICATIONS FOR PRACTICE: The poly(ADP-ribose) polymerase (PARP) inhibitor olaparib has recently received approval from the Food and Drug Administration (FDA) and European Medicines Agency (EMA), with a second agent (rucaparib) likely to be approved in the near future. However, the patient population with potential benefit from PARP inhibitors is likely wider than that of germline BRCA mutation-associated disease, and biomarkers are in development to enable the selection of patients with the potential for clinical benefit from these agents. Questions remain regarding the toxicities of PARP inhibitors, limiting the use of these agents in the prophylactic or adjuvant setting until more information is available. The indications for olaparib as indicated by the FDA and EMA are reviewed.

Incidence of resistance to benzimidazole fungicides in a field population of Venturia inaequalis /

The allele-specific polymerase chain reaction (PCR) was used to screen for the presence of benomyl resistance, and to characterize their levels and frequencies in field populations of Venturia inaequalis during two seasons. Three hundred isolates of V. inaequalis were collected each season from infected leaves of MalusX domestica. Borkh c.v. Mcintosh. The trees used were sprayed in the year prior to collection with five applications of benomyl, its homologue Azindoyle, or water. Monoconidial isolates of V. inaequalis were grown on 2% potato dextrose agar (PDA) for four weeks. Each isolate was taken from a single lesion from a single leaf. Total genomic DNA was extracted from the four week old colonies of V. inaequalis, prepared and used as a template in PCR reactions. PCR reactions were achieved by utilizing allele-specific primers. Each primer was designed to amplify fragments from a specific allele. Primer Vin was specific for mutations conferring the ben^^"^ phenotype. It was expected to amplify a 171 bp. DNA fragment from the ben^"^ alleles only. Primers BenHR and BenMR were specific for mutations conferring the ben"" and ben'^'' phenotypes, respectively. They were expected to amplify 172 bp. and 165 bp. DNA fragments from the ben"" and ben"^" alleles, respectively. Of the 953 isolates tested, 414 (69.9%) were benomyl sensitive (ben^) and 179 (30.1%) were benomyl resistant. All the benomyl resistant alleles were ben^"", since neither the ben"" nor the ben"" alleles were detected. Frequencies of benomyl resistance were 23%, 24%, and 23% for the 1997 collections, and were 46%, 26% and 38% for the 1998 collections for benomyl, Azindoyle and water treatments, respectively. Growth assay was performed to evaluate the applicability of using PCR in monitoring benomyl resistance in fungal field populations. Tests were performed on 14 isolates representing the two phenotypes (ben^ and ben^"'' alleles) characterized by PCR. Results of those tests were in agreement with PCR results. Enzyme digestion was also used to evaluate the accuracy and reliability of PCR products. The mutation associated with the ben^"'' phenotype creates a unique site for the endonuclease enzyme Bsh^236^ allowing the use of enzyme digestion. Isolates characterized by PCR as ben^'^'^ alleles had this restriction site for the SsA7l2361 enzyme. The most time consuming aspect of this study was growing fungal isolates on culture media for DNA extraction. In addition, the risk of contamination or losing the fungus during growth processes was relatively high. A technique for extracting DNA directly from lesions on leaves has been used (Luck and Gillings 1 995). In order to apply this technique in experiments designed to monitor fungicide resistance, a lesion has to be homogeneous for fungicide sensitivity. For this purpose, PCR protocol was used to determine lesion homogeneity. One hundred monoconidial isolates of V. inaequalis from 10 lesions (10-conidia/ lesion) were tested for their phenotypes with respect to benomyl sensitivity. Conidia of six lesions were homogeneous, while conidia of the remaining lesions were mixtures of ben^ and ben^ phenotypes. Neither the ben" nor the ben' phenotype was detected.