Mutations in the Proenteropeptidase Gene Are the Molecular Cause of Congenital Enteropeptidase Deficiency

Enteropeptidase (enterokinase [E.C.3.4.21.9]) is a serine protease of the intestinal brush border in the proximal small intestine. It activates the pancreatic proenzyme trypsinogen, which, in turn, releases active digestive enzymes from their inactive pancreatic precursors. Congenital enteropeptidase deficiency is a rare recessively inherited disorder leading, in affected infants, to severe failure to thrive. The genomic structure of the proenteropeptidase gene (25 exons, total gene size 88 kb) was characterized in order to perform DNA sequencing in three clinically and biochemically proved patients with congenital enteropeptidase deficiency who were from two families. We found compound heterozygosity for nonsense mutations (S712X/R857X) in two affected siblings and found compound heterozygosity for a nonsense mutation (Q261X) and a frameshift mutation (FsQ902) in the third patient. In accordance with the biochemical findings, all four defective alleles identified are predicted null alleles leading to a gene product not containing the active site of the enzyme. These data provide first evidence that proenteropeptidase-gene mutations are the primary cause of congenital enteropeptidase deficiency.     

Novel Interaction of Ornithine Decarboxylase with Sepiapterin Reductase Regulates Neuroblastoma Cell Proliferation

Ornithine decarboxylase (ODC) is the sentinel enzyme in polyamine biosynthesis. Both ODC and polyamines regulate cell division, proliferation, and apoptosis. Sepiapterin reductase (SPR) catalyzes the last step in the biosynthesis of tetrahydrobiopterin (BH₄), an essential cofactor of nitric oxide synthase, and has been implicated in neurological diseases but not yet in cancer. In this study, we present compelling evidence that native ODC and SPR physically interact, and we defined the individual amino acid residues involved in both enzymes using in silico protein–protein docking simulations. The resulting heterocomplex is a surprisingly compact structure, featuring two energetically and structurally equivalent binding modes both in monomer and in dimer conformations. The novel interaction between ODC and SPR proteins was confirmed under physiological conditions by co-immunoprecipitation and co-localization in neuroblastoma (NB) cells. Importantly, we showed that siRNA (small interfering RNA)-mediated knockdown of SPR expression significantly reduced endogenous ODC enzyme activity in NB cells, thus demonstrating the biological relevance of the ODC–SPR interaction. Finally, in a cohort of 88 human NB tumors, we found that high SPR mRNA expression correlated significantly with poor survival prognosis using a Kaplan–Meier analysis (log-rank test, P = 5 × 10^− 4), suggesting an oncogenic role for SPR in NB tumorigenesis. In conclusion, we showed that ODC binds SPR and thus propose a new concept in which two well-characterized biochemical pathways converge via the interaction of two enzymes. We identified SPR as a novel regulator of ODC enzyme activity and, based on clinical evidence, present a model in which SPR drives ODC-mediated malignant progression in NB.     

Novel Mutations in the Human HPRT Gene

Inherited mutation of a purine salvage enzyme, hypoxanthine guanine phosphoribosyltransferase (HPRT), gives rise to Lesch-Nyhan Syndrome (LNS) or HPRT-related gout. Here, we report five novel independent mutations in the coding region of the HPRT gene from five unrelated male patients manifesting different clinical phenotypes associated with LNS: exon 2: c.133A > G, p.45R > G; c.35A > C, p.12D > A; c.88delG; exon 7: c.530A > T, p.177D > V; and c.318 + 1G > C: IVS3 + 1G > C splice site mutation.     

Detection of a Novel Sepiapterin Reductase mRNA: Assay of mRNA in Various Cells and Tissues of Various Species

Fragments of cDNA coding for rat, murine, and human sepiapterin reductase (SR) were amplified by PCR via primer positioning close to the reported 3′-end of the coding region in the rat enzyme. They were sequenced and used as probes for mRNA detection. Northern blot analysis detected two mRNA species for SR. Their sizes were 1.3 and 2.1 kb for rat, 1.3 and 2.3 kb for mouse, and 1.6 and 2.1 kb for human cell lines. Comparison of rat cell lines and rat tissues indicated that in tissues only the 1.3-kb species is present. Washing of the Northern blots under different stringency conditions indicated a more stable interaction of the 1.3-kb mRNA species with the cDNA probe as compared to the 2.3-kb species. The 1.3-kb species corresponds to the reported 28.2-kDa molecular mass of rat SR monomer. SR mRNA expression is absent in the human NK-like cell line YT and in the murine erythroleukemia subclone B8/3, which both lack SR activity. Moreover, the relative mRNA expression correlates with the enzymatic activities of different cell lines within the same species. This indicates that SR activity is regulated by its steady state mRNA levels.     

Sepiapterin Reductase Mediates Chemical Redox Cycling in Lung Epithelial Cells

In the lung, chemical redox cycling generates highly toxic reactive oxygen species that can cause alveolar inflammation and damage to the epithelium, as well as fibrosis. In this study, we identified a cytosolic NADPH-dependent redox cycling activity in mouse lung epithelial cells as sepiapterin reductase (SPR), an enzyme important for the biosynthesis of tetrahydrobiopterin. Human SPR was cloned and characterized. In addition to reducing sepiapterin, SPR mediated chemical redox cycling of bipyridinium herbicides and various quinones; this activity was greatest for 1,2-naphthoquinone followed by 9,10-phenanthrenequinone, 1,4-naphthoquinone, menadione, and 2,3-dimethyl-1,4-naphthoquinone. Whereas redox cycling chemicals inhibited sepiapterin reduction, sepiapterin had no effect on redox cycling. Additionally, inhibitors such as dicoumarol, N-acetylserotonin, and indomethacin blocked sepiapterin reduction, with no effect on redox cycling. Non-redox cycling quinones, including benzoquinone and phenylquinone, were competitive inhibitors of sepiapterin reduction but noncompetitive redox cycling inhibitors. Site-directed mutagenesis of the SPR C-terminal substrate-binding site (D257H) completely inhibited sepiapterin reduction but had minimal effects on redox cycling. These data indicate that SPR-mediated reduction of sepiapterin and redox cycling occur by distinct mechanisms. The identification of SPR as a key enzyme mediating chemical redox cycling suggests that it may be important in generating cytotoxic reactive oxygen species in the lung. This activity, together with inhibition of sepiapterin reduction by redox-active chemicals and consequent deficiencies in tetrahydrobiopterin, may contribute to tissue injury.     

Rapsyn Mutations in Humans Cause Endplate Acetylcholine-Receptor Deficiency and Myasthenic Syndrome

Congenital myasthenic syndromes (CMSs) stem from genetic defects in endplate (EP)-specific presynaptic, synaptic, and postsynaptic proteins. The postsynaptic CMSs identified to date stem from a deficiency or kinetic abnormality of the acetylcholine receptor (AChR). All CMSs with a kinetic abnormality of AChR, as well as many CMSs with a deficiency of AChR, have been traced to mutations in AChR-subunit genes. However, in a subset of patients with EP AChR deficiency, the genetic defect has remained elusive. Rapsyn, a 43-kDa postsynaptic protein, plays an essential role in the clustering of AChR at the EP. Seven tetratricopeptide repeats (TPRs) of rapsyn subserve self-association, a coiled-coil domain binds to AChR, and a RING-H2 domain associates with beta-dystroglycan and links rapsyn to the subsynaptic cytoskeleton. Rapsyn self-association precedes recruitment of AChR to rapsyn clusters. In four patients with EP AChR deficiency but with no mutations in AChR subunits, we identify three recessive rapsyn mutations: one patient carries L14P in TPR1 and N88K in TPR3; two are homozygous for N88K; and one carries N88K and 553ins5, which frameshifts in TPR5. EP studies in each case show decreased staining for rapsyn and AChR, as well as impaired postsynaptic morphological development. Expression studies in HEK cells indicate that none of the mutations hinders rapsyn self-association but that all three diminish coclustering of AChR with rapsyn.     

Identification of Novel Mutations in the Human HPRT Gene

Inherited mutation of the purine salvage enzyme, hypoxanthine guanine phosphoribosyltransferase (HPRT) gives rise to Lesch–Nyhan syndrome (LNS) or Lesch–Nyhan variants (LNVs). We report three novel independent mutations in the coding region of HPRT gene: exon 3: c.141delA, p.D47fs53X; exon 5: c.400G>A, p.E134K; exon 7: c.499A>G, p.R167G from three LNS affected male patients.     

Mutations in the unc-41 Gene Cause Elevation of Acetylcholine Levels

Abstract: Mutations in the Caenorhabditis elegans unc-41 gene result in an allele-dependent elevation of acetylcholine content. Eight recessive alleles ( cn252, e268, e399, e650, e1175, e1199, e1294, and e870 ) lead to phenotypes including uncoordinated locomotion, slow growth, a small mature body, and resistance to the acetylcholinesterase inhibitors as well as the elevation of acetylcholine content. The remaining two alleles, e554 and e1162 , exhibit normal acetylcholine levels but display the short-body phenotype in a semidominant way. To determine the localization of the elevated acetylcholine content, a method for the isolation of synaptic vesicles from C. elegans was established. The elevation of acetylcholine content in the unc-41 mutants is accompanied by the accumulation of synaptic vesicles. We propose that at least one function of the unc-41 gene relates to the release of neurotransmitters.     

Novel KRAS Gene Mutations in Sporadic Colorectal Cancer

Introduction

In this article, we report 7 novel KRAS gene mutations discovered while retrospectively studying the prevalence and pattern of KRAS mutations in cancerous tissue obtained from 56 Saudi sporadic colorectal cancer patients from the Eastern Province.

Methods

Genomic DNA was extracted from formalin-fixed, paraffin-embedded cancerous and noncancerous colorectal tissues. Successful and specific PCR products were then bi-directionally sequenced to detect exon 4 mutations while Mutector II Detection Kits were used for identifying mutations in codons 12, 13 and 61. The functional impact of the novel mutations was assessed using bioinformatics tools and molecular modeling.

Results

KRAS gene mutations were detected in the cancer tissue of 24 cases (42.85%). Of these, 11 had exon 4 mutations (19.64%). They harbored 8 different mutations all of which except two altered the KRAS protein amino acid sequence and all except one were novel as revealed by COSMIC database. The detected novel mutations were found to be somatic. One mutation is predicted to be benign. The remaining mutations are predicted to cause substantial changes in the protein structure. Of these, the Q150X nonsense mutation is the second truncating mutation to be reported in colorectal cancer in the literature.

Conclusions

Our discovery of novel exon 4 KRAS mutations that are, so far, unique to Saudi colorectal cancer patients may be attributed to environmental factors and/or racial/ethnic variations due to genetic differences. Alternatively, it may be related to paucity of clinical studies on mutations other than those in codons 12, 13, 61 and 146. Further KRAS testing on a large number of patients of various ethnicities, particularly beyond the most common hotspot alleles in exons 2 and 3 is needed to assess the prevalence and explore the exact prognostic and predictive significance of the discovered novel mutations as well as their possible role in colorectal carcinogenesis.     

Heterozygous Germline Mutations in the CBL Tumor-Suppressor Gene Cause a Noonan Syndrome-like Phenotype

RAS signaling plays a key role in controlling appropriate cell responses to extracellular stimuli and participates in early and late developmental processes. Although enhanced flow through this pathway has been established as a major contributor to oncogenesis, recent discoveries have revealed that aberrant RAS activation causes a group of clinically related developmental disorders characterized by facial dysmorphism, a wide spectrum of cardiac disease, reduced growth, variable cognitive deficits, ectodermal and musculoskeletal anomalies, and increased risk for certain malignancies. Here, we report that heterozygous germline mutations in CBL, a tumor-suppressor gene that is mutated in myeloid malignancies and encodes a multivalent adaptor protein with E3 ubiquitin ligase activity, can underlie a phenotype with clinical features fitting or partially overlapping Noonan syndrome (NS), the most common condition of this disease family. Independent CBL mutations were identified in two sporadic cases and two families from among 365 unrelated subjects who had NS or suggestive features and were negative for mutations in previously identified disease genes. Phenotypic heterogeneity and variable expressivity were documented. Mutations were missense changes altering evolutionarily conserved residues located in the RING finger domain or the linker connecting this domain to the N-terminal tyrosine kinase binding domain, a known mutational hot spot in myeloid malignancies. Mutations were shown to affect CBL-mediated receptor ubiquitylation and dysregulate signal flow through RAS. These findings document that germline mutations in CBL alter development to cause a clinically variable condition that resembles NS and that possibly predisposes to malignancies.     

COQ4 Mutations Cause a Broad Spectrum of Mitochondrial Disorders Associated with CoQ10 Deficiency

Primary coenzyme Q10 (CoQ₁₀) deficiencies are rare, clinically heterogeneous disorders caused by mutations in several genes encoding proteins involved in CoQ₁₀ biosynthesis. CoQ₁₀ is an essential component of the electron transport chain (ETC), where it shuttles electrons from complex I or II to complex III. By whole-exome sequencing, we identified five individuals carrying biallelic mutations in COQ4. The precise function of human COQ4 is not known, but it seems to play a structural role in stabilizing a multiheteromeric complex that contains most of the CoQ₁₀ biosynthetic enzymes. The clinical phenotypes of the five subjects varied widely, but four had a prenatal or perinatal onset with early fatal outcome. Two unrelated individuals presented with severe hypotonia, bradycardia, respiratory insufficiency, and heart failure; two sisters showed antenatal cerebellar hypoplasia, neonatal respiratory-distress syndrome, and epileptic encephalopathy. The fifth subject had an early-onset but slowly progressive clinical course dominated by neurological deterioration with hardly any involvement of other organs. All available specimens from affected subjects showed reduced amounts of CoQ₁₀ and often displayed a decrease in CoQ₁₀-dependent ETC complex activities. The pathogenic role of all identified mutations was experimentally validated in a recombinant yeast model; oxidative growth, strongly impaired in strains lacking COQ4, was corrected by expression of human wild-type COQ4 cDNA but failed to be corrected by expression of COQ4 cDNAs with any of the mutations identified in affected subjects. COQ4 mutations are responsible for early-onset mitochondrial diseases with heterogeneous clinical presentations and associated with CoQ10 deficiency.     

Mutations in C10orf11, a Melanocyte-Differentiation Gene,Cause Autosomal-Recessive Albinism

Autosomal-recessive albinism is a hypopigmentation disorder with a broad phenotypic range. A substantial fraction of individuals with albinism remain genetically unresolved, and it has been hypothesized that more genes are to be identified. By using homozygosity mapping of an inbred Faroese family, we identified a 3.5 Mb homozygous region (10q22.2–q22.3) on chromosome 10. The region contains five protein-coding genes, and sequencing of one of these, C10orf11, revealed a nonsense mutation that segregated with the disease and showed a recessive inheritance pattern. Investigation of additional albinism-affected individuals from the Faroe Islands revealed that five out of eight unrelated affected persons had the nonsense mutation in C10orf11. Screening of a cohort of autosomal-recessive-albinism-affected individuals residing in Denmark showed a homozygous 1 bp duplication in C10orf11 in an individual originating from Lithuania. Immunohistochemistry showed localization of C10orf11 in melanoblasts and melanocytes in human fetal tissue, but no localization was seen in retinal pigment epithelial cells. Knockdown of the zebrafish (Danio rerio) homolog with the use of morpholinos resulted in substantially decreased pigmentation and a reduction of the apparent number of pigmented melanocytes. The morphant phenotype was rescued by wild-type C10orf11, but not by mutant C10orf11. In conclusion, we have identified a melanocyte-differentiation gene, C10orf11, which when mutated causes autosomal-recessive albinism in humans.     

Mutations in PYCR2, Encoding Pyrroline-5-Carboxylate Reductase 2, Cause Microcephaly and Hypomyelination

Despite recent advances in understanding the genetic bases of microcephaly, a large number of cases of microcephaly remain unexplained, suggesting that many microcephaly syndromes and associated genes have yet to be identified. Here, we report mutations in PYCR2, which encodes an enzyme in the proline biosynthesis pathway, as the cause of a unique syndrome characterized by postnatal microcephaly, hypomyelination, and reduced cerebral white-matter volume. Linkage mapping and whole-exome sequencing identified homozygous mutations (c.355C>T [p.Arg119Cys] and c.751C>T [p.Arg251Cys]) in PYCR2 in the affected individuals of two consanguineous families. A lymphoblastoid cell line from one affected individual showed a strong reduction in the amount of PYCR2. When mutant cDNAs were transfected into HEK293FT cells, both variant proteins retained normal mitochondrial localization but had lower amounts than the wild-type protein, suggesting that the variant proteins were less stable. A PYCR2-deficient HEK293FT cell line generated by genome editing with the clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 system showed that PYCR2 loss of function led to decreased mitochondrial membrane potential and increased susceptibility to apoptosis under oxidative stress. Morpholino-based knockdown of a zebrafish PYCR2 ortholog, pycr1b, recapitulated the human microcephaly phenotype, which was rescued by wild-type human PYCR2 mRNA, but not by mutant mRNAs, further supporting the pathogenicity of the identified variants. Hypomyelination and the absence of lax, wrinkly skin distinguishes this condition from that caused by previously reported mutations in the gene encoding PYCR2’s isozyme, PYCR1, suggesting a unique and indispensable role for PYCR2 in the human CNS during development.     

缺铁胁迫下4种果树砧木中三价铁螯合物还原酶基因的表达

用活力染色法观测 4种果树砧木中FCR基因表达的结果表明 ,小金海棠 (M .xiaojinensis)和香橙 (C .junos)在缺铁胁迫下根吸收区FCR活性明显增强 ,增强幅度显著强于丽江山荆子 (M .rockii)和枳 (P .trifoliata)。用拟南芥的FCR基因 (FRO2 )做探针 ,进行组织印迹的RNANorthern杂交。结果表明 ,在缺铁胁迫下 ,在小金海棠和香橙中均有与FRO2类似基因的强烈表达 ,而在同样胁迫条件下的枳和丽江山荆子中表达却很微弱。这种分子水平上的反应与通常所熟知的生理反应是一致的 ,说明小金海棠和香橙忍耐缺铁环境的生理机制和分子基础类似 ,FCR在它们忍耐缺铁的生化反应中起着非常重要的作用 ,FCR基因在 4种果树砧木中的表达水平高低与它们忍耐缺铁的能力呈现正相关。并且 ,在小金海棠和香橙的根、茎、叶等营养器官的特定组织细胞中 ,均能检出高水平的FCR基因转录产物 ,表明耐缺铁能力强的小金海棠和香橙体内存在高效的铁运输和利用机制     

Mutations in the Fatty Acid Transport Protein 4 Gene Cause the Ichthyosis Prematurity Syndrome

Ichthyosis prematurity syndrome (IPS) is an autosomal-recessive disorder characterized by premature birth and neonatal asphyxia, followed by a lifelong nonscaly ichthyosis with atopic manifestations. Here we show that the gene encoding the fatty acid transport protein 4 (FATP4) is mutated in individuals with IPS. Fibroblasts derived from a patient with IPS show reduced activity of very long-chain fatty acids (VLCFA)-CoA synthetase and a specific reduction in the incorporation of VLCFA into cellular lipids. The human phenotype is consistent with Fatp4 deficiency in mice that is characterized by a severe skin phenotype, a defective permeability barrier function, and perturbed VLCFA metabolism. Our results further emphasize the importance of fatty acid metabolism for normal epidermal barrier function illustrated by deficiency of a member in the FATP family of proteins.     

Two Novel De Novo GARS Mutations Cause Early-Onset Axonal Charcot-Marie-Tooth Disease

Background

Mutations in the GARS gene have been identified in a small number of patients with Charcot-Marie-Tooth disease (CMT) type 2D or distal spinal muscular atrophy type V, for whom disease onset typically occurs during adolescence or young adulthood, initially manifesting as weakness and atrophy of the hand muscles. The role of GARS mutations in patients with inherited neuropathies in Taiwan remains elusive.

Methodology and Principal Findings

Mutational analyses of the coding regions of GARS were performed using targeted sequencing of 54 patients with molecularly unassigned axonal CMT, who were selected from 340 unrelated CMT patients. Two heterozygous mutations in GARS, p.Asp146Tyr and p.Met238Arg, were identified; one in each patient. Both are novel de novo mutations. The p.Asp146Tyr mutation is associated with a severe infantile-onset neuropathy and the p.Met238Arg mutation results in childhood-onset disability.

Conclusion

GARS mutations are an uncommon cause of CMT in Taiwan. The p.Asp146Tyr and p.Met238Arg mutations are associated with early-onset axonal CMT. These findings broaden the mutational spectrum of GARS and also highlight the importance of considering GARS mutations as a disease cause in patients with early-onset neuropathies.     

Mutations in the Human Ca2+-Sensing-Receptor Gene That Cause Familial Hypocalciuric Hypercalcemia

We report five novel mutations in the human Ca²⁺-sensing-receptor gene that cause familial hypocalciuric hypercalcemia (FHH) or neonatal severe hyperparathyroidism. Each gene defect is a missense mutation (²²⁸Arg→Gln, ¹³⁹Thr→Met, ¹⁴⁴Gly→Glu, ⁶³Arg→Met, and ⁶⁷Arg→Cys) that encodes a nonconservative amino acid alteration. These mutations are each predicted to be in the Ca²⁺-sensing receptor's large extracellular domain. In three families with FHH linked to the Ca²⁺-sensing-receptor gene on chromosome 3 and in unrelated individuals probands with FHH, mutations were not detected in protein-coding sequences. On the basis of these data and previous analyses, we suggest that there are a wide range of mutations that cause FHH. Mutations that perturb the structure and function of the extracellular or transmembrane domains of the receptor and those that affect noncoding sequences of the Ca²⁺-sensing-receptor gene can cause FHH.