Phenotype In Heterozygotes Research Articles

Alteraciones hepáticas por déficit de alfa-1-antitripsina en adultos. Estudio de 5 pacientes y análisis de los casos publicados en la bibliografía española

To determine the epidemiological characteristics of liver disease secondary to alpha-1-antitrypsin deficiency and associated processes in the Spanish population. We reviewed the medical records of adults with liver abnormalities due to alpha-1-antitrypsin deficiency diagnosed between 1981 and 2001 in the Hospital Donosti in San Sebastian (Spain) as well as the cases published in the literature before 1999. Diagnosis was based on clinical and biochemical data, imaging tests and/or liver biopsy and/or necroscopy together with serum values of alpha-1-antitrypsin and phenotyping. Fifty cases of liver disease secondary to alpha-1-antitrypsin deficiency (45 from the literature and 5 from our hospital) were included. There were 34 men and 16 women aged between 18 and 77 years. Fifteen (30%) had relatives with alpha-1-antitrypsin deficiency. Hepatitis and/or neonatal cholestasis were confirmed in 4 and alcoholism was confirmed in 17. Of the series, 8 (16%) had portal fibrosis and 29 (58%) had cirrhosis. Cirrhosis was mainly macro-micronodular and was decompensated in 48% of the cases. Of the patients with cirrhosis, 12 were ZZ homozygotes and 12 were heterozygotes, mainly MZ and SZ. The most frequent associated process was respiratory disease (emphysema and/or chronic bronchitis) in 25 of the 50 cases (50%). The presence of cirrhosis in alpha-1-antitrypsin deficiency is low, approximately 2.2/100,000 for ZZ homozygotes. Age at diagnosis of cirrhosis or fibrosis was more than 50 years. The male-to-female ratio was 2 to 1. In one-third of the patients alcohol could have been a coadjuvant or aggravating factor in the liver disease. No differences were found between homo- and heterozygote phenotypes in patients with cirrhosis. The most frequently associated processes were respiratory diseases due to alpha-1-antitrypsin deficiency.

Genetic‐epidemiological study of schizophrenia with the beginning in the young age

The aim of investigation was the study of factors spreading in population and families of schizophrenia with consideration the age to the moment of manifestation. There were studied 476 schizophrenia disordered persons, included in Tomsk epidemiological register (ER) of schizophrenia. The age to the moment of manifestation of schizophrenia was registered in the age of disordered persons by the moment of the beginning psychotical displays of disorders. The disease began in the interval from 15 to 60 years.In the population is spreading mostly schizophrenia with the age of manifestation from 15 to 45 years: from 5.2 disordered persons in the age of 15–19‐year‐old‐to 2.4 disordered persons in the age of 40–44‐year‐old‐on a 10 000 of whole population. The most intensive indicator was noted in the age of 20–24 years old – 6.5 disordered persons on a 10 000 of population.There were shared two groups ofdisordered persons: with the beginning of disorder in the age of 15–24 years old (young age) – 196 disordered persons, in the age of 25–44 years old (mature age) – 254 disordered persons. Different clinical forms described these groups and specialties of display the schizophrenia diseases.There were studied 332 families of disordered persons ER. The relatives of fist degree of probands with the beginning of disease in young age were ill with schizophrenia two times more, then relatives of probands with the beginning of disease in mature age (3.5 and 1.8%, correspondingly). Analysis of multifactorial threshold model (MFT) showed that a whole contribution of genetic factors – additive genetic component – by the beginning of schizophrenia in 15–24‐year‐old‐was 62.1%, residual environmental factors was 31.4%. Single major locus model (SML) revealed, that the probability of appearing disease in the age of 15–24 years old (p1) of mutant homozygotes AA is equal to 33%. In time less displayed pathological phenotype of heterozygotes they Aa (p2=2,3%). The majority of schizophrenia disordered persons in young age (72.6%) are heterozygotes, homozygotes are 27.4%. In the young age are ill schizophrenia homozygotes carrier of pathological genotype with increased genetically predisposition and increased probability its display more often.

A heterozygote phenotype is present in the jvs +/− mutant mouse livers

The juvenile visceral steatosis ( jvs) mouse, having a mutation in the carnitine transporter gene Octn2, is a model of primary systemic carnitine deficiency in humans (SCD, OMIM 212140). Like humans with SCD, homozygous jvs −/− mice have hepatic and cardiac steatoses, reduced plasma and tissue carnitines, and increased urinary carnitine clearance. Because symptomatic heterozygotes have been reported for some fatty acid oxidation disorders, including SCD, we compared the jvs heterozygotes to normal control mice. We measured the free and esterified carnitine, total cholesterol, and triglycerides in adult liver samples, myocardium, and skeletal muscle. Our results indicate significant differences between the livers of nonfasting adult normal ( n=8) vs jvs heterozygotes ( n=8) ( means± SEM, p<0.01) for the following parameters: free carnitine, 2.28±0.36 nmol/ mg protein vs 0.41±0.13; total carnitine, 3.48±0.36 vs 1.27±0.25; triglycerides, 0.14±0.04 vs 0.39±0.02; and total cholesterol, 0.21±0.02 vs 0.39±0.04, but not for esterified carnitine, 1.18±0.17 vs 0.90±0.17 ( p>0.05). There is also a negative correlation between hepatic free carnitine and triglycerides from jvs heterozygotes ( p<0.05). Similar results were obtained with myocardium and skeletal muscle. We conclude that free and total carnitine levels are significantly lower in the heterozygote mouse liver and heart while triglyceride and total cholesterol levels are significantly higher. We speculate that in situations of lipolytic stress, some SCD heterozygotes might develop clinical symptoms of carnitine deficiency.

Influence of deficient α1-anti-trypsin phenotypes on clinical characteristics and severity of asthma in adults

Severe α1-anti-trypsin (AAT) deficiency implies a high risk of pulmonary emphysema development. The possible relationship between partial deficiencies of this enzyme and bronchial asthma remains controversial. The objective of this study was to ascertain the distribution of AAT phenotypes in a non-selected asthmatic patient population. A cross-sectional study on a sample of 111 patients with asthma was carried out. Demographic and clinical variables were collected with serum IgE concentrations, plasma eosinophil number and serum AAT concentrations determined, together with the Pi phenotype. Asthma was mild in 36 (32·4%) patients, moderate in 45 (40·5%) and severe in 30 (27%). No differences were observed in eosinophil count or serum IgE or AAT concentrations among patients with different degrees of severity. Twenty-two (19·8%) asthmatics with deficient phenotypes for AAT were identified, distributed equally in all severity stages of the disease. No significant differences were found in clinical and functional characteristics, or in asthma morbidity between PiMM and PiMS patients or the heterozygote group (PiMS and PiMZ). Eosinophil count and IgE concentrations did not differ significantly between asthmatics with normal phenotype and heterozygotes. In conclusion, the distribution of AAT phenotypes in asthmatic patients did not differ from that found in the general population. Heterozygote phenotypes for the deficiency do not appear to confer greater severity or different clinical expression of asthma in adults.

Frequency of the S65C mutation of HFE and iron overload in 309 subjects heterozygous for C282Y

Background/Aims : HFE -related haemochromatosis is a common disorder of iron metabolism. Most affected individuals are homozygous for the C282Y mutation of HFE . Some are compound heterozygotes for C282Y/H63D. A small proportion have neither of these genotypes. We have investigated the phenotype of compound heterozygotes for C282Y and another missense mutation S65C. Methods : Genotype for the S65C mutation was determined in 309 subjects heterozygous for C282Y and negative for H63D, referred because of increased serum iron indices or family screening. A control sample comprising 315 individuals was also studied. Results : Twelve individuals were compound heterozygotes for C282Y and S65C. Seven, referred for family screening, had normal serum iron indices. Five subjects had elevated serum iron indices; three of these had elevated hepatic iron and have received treatment for iron overload. Transferrin saturation was significantly elevated in C282Y/S65C compound heterozygotes compared with simple C282Y heterozygotes. Conclusions : Some C282Y/S65C compound heterozygotes have elevated serum iron indices and iron overload. The penetrance of this genotype is low and other genetic and environmental factors may influence the expression of iron loading. Screening for S65C may be useful in individuals with iron overload who are not homozygous for C282Y or compound heterozygous for C282Y/H63D.

Functional analysis of mutations in SLC7A9, and genotype-phenotype correlation in non-Type I cystinuria.

Cystinuria (OMIM 220100) is a common recessive disorder of renal reabsorption of cystine and dibasic amino acids that results in nephrolithiasis of cystine. Mutations in SLC3A1, which encodes rBAT, cause Type I cystinuria, and mutations in SLC7A9, which encodes a putative subunit of rBAT (b(o,+)AT), cause non-Type I cystinuria. Here we describe the genomic structure of SLC7A9 (13 exons) and 28 new mutations in this gene that, together with the seven previously reported, explain 79% of the alleles in 61 non-Type I cystinuria patients. These data demonstrate that SLC7A9 is the main non-Type I cystinuria gene. Mutations G105R, V170M, A182T and R333W are the most frequent SLC7A9 missense mutations found. Among heterozygotes carrying these mutations, A182T heterozygotes showed the lowest urinary excretion values of cystine and dibasic amino acids. Functional analysis of mutation A182T after co-expression with rBAT in HeLa cells revealed significant residual transport activity. In contrast, mutations G105R, V170M and R333W are associated to a complete or almost complete loss of transport activity, leading to a more severe urinary phenotype in heterozygotes. SLC7A9 mutations located in the putative transmembrane domains of b(o,+)AT and affecting conserved amino acid residues with a small side chain generate a severe phenotype, while mutations in non-conserved residues give rise to a mild phenotype. These data provide the first genotype-phenotype correlation in non-Type I cystinuria, and show that a mild urinary phenotype in heterozygotes may associate with mutations with significant residual transport activity.

Clinical and hematological features of codon 17, A-T mutation of beta-thalassemia in Thai patients.

Forty-one patients with codon 17, A-T mutation of beta-thalassemia, which is commonly found in Thailand, were studied to determine whether it is possible to predict phenotypic severity from genetic factors. The clinical phenotype of homozygotes for codon 17, A-T and compound heterozygotes for codon 17, A-T and beta+-thalassemia may be used to predict a severe phenotype with TM. However, the clinical phenotype of compound heterozygotes for codon 17, A-T and beta+-thalassemia or Hb E were variable and could not be accurately predicted. The association of alpha-thalassemia2 and milder disease was and was not evident in patients with codon 17, A-T and Hb E. The association between Hb CS gene or the presence of XmnI-Ggamma polymorphism and a mild clinical phenotype is not apparent, indicating the involvement of other ameliorating determinants or genetic modifications.

Increased Insulin Sensitivity in Gsα Knockout Mice

The stimulatory guanine nucleotide-binding protein (G(s)) is required for hormone-stimulated cAMP generation. Gnas, the gene encoding the G(s) alpha-subunit, is imprinted, and targeted disruption of this gene in mice leads to distinct phenotypes in heterozygotes depending on whether the maternal (m-/+) or paternal (+/p-) allele is mutated. Notably, m-/+ mice become obese, whereas +/p- mice are thinner than normal. In this study we show that despite these opposite changes in energy metabolism, both m-/+ and +/p- mice have greater sensitivity to insulin, with low to normal fasting glucose levels, low fasting insulin levels, improved glucose tolerance, and exaggerated hypoglycemic response to administered insulin. The combination of increased insulin sensitivity with obesity in m-/+ mice is unusual, because obesity is typically associated with insulin resistance. In skeletal muscles isolated from both m-/+ and +/p- mice, the basal rate of 2-deoxyglucose uptake was normal, whereas the rate of 2-deoxyglucose uptake in response to maximal insulin stimulation was significantly increased. The similar changes in muscle sensitivity to insulin in m-/+ and +/p- mice may reflect the fact that muscle G(s)alpha expression is reduced by approximately 50% in both groups of mice. GLUT4 expression is unaffected in muscles from +/p- mice. Increased responsiveness to insulin is therefore the result of altered insulin signaling and/or GLUT4 translocation. This is the first direct demonstration in a genetically altered in vivo model that G(s)-coupled pathways negatively regulate insulin signaling.

Age and residual cholesterol efflux affect HDL cholesterol levels and coronary artery disease in ABCA1 heterozygotes.

We and others have recently identified mutations in the ABCA1 gene as the underlying cause of Tangier disease (TD) and of a dominantly inherited form of familial hypoalphalipoproteinemia (FHA) associated with reduced cholesterol efflux. We have now identified 13 ABCA1 mutations in 11 families (five TD, six FHA) and have examined the phenotypes of 77 individuals heterozygous for mutations in the ABCA1 gene. ABCA1 heterozygotes have decreased HDL cholesterol (HDL-C) and increased triglycerides. Age is an important modifier of the phenotype in heterozygotes, with a higher proportion of heterozygotes aged 30-70 years having HDL-C greater than the fifth percentile for age and sex compared with carriers less than 30 years of age. Levels of cholesterol efflux are highly correlated with HDL-C levels, accounting for 82% of its variation. Each 8% change in ABCA1-mediated efflux is predicted to be associated with a 0.1 mmol/l change in HDL-C. ABCA1 heterozygotes display a greater than threefold increase in the frequency of coronary artery disease (CAD), with earlier onset than unaffected family members. CAD is more frequent in those heterozygotes with lower cholesterol efflux values. These data provide direct evidence that impairment of cholesterol efflux and consequently reverse cholesterol transport is associated with reduced plasma HDL-C levels and increased risk of CAD.

Neuronal ceroid lipofuscinoses: research update.

This study describes the phenotype/genotype analysis of 159 probands with neuronal ceroid lipofuscinosis (37 CLN1, 72 classic CLN2, 10 variant LINCL, and 40 CLN3) collected at the New York State Institute for Basic Research in Developmental Disabilities (IBR). Phenotype/genotype comparison showed that mutations in the CLN1 gene were associated with different phenotypes: infantile, late infantile, and juvenile. Two common mutations (223A-->C and 451C-->T) were found in 26 of 37 CLN1 subjects (64% of alleles examined). A nonsense point mutation, 451C-->T, was the most common in CLN1 subjects with infantile onset at 0-2 years, accounting for 50% of alleles studied. A missense point mutation, 223A-->C, was the most common among CLN1 subjects with juvenile onset older than 4 years, accounting for 45% of alleles examined. Twenty-one other CLN1 mutations were identified in 4 of 37 subjects with infantile onset, 6 of 37 with late-infantile onset, and 6 of 37 with juvenile onset. All CLN1 probands were palmitoyl-protein thioesterase (PPT)-deficient and showed granular osmiophilic deposits (GROD) at the electron microscopic (EM) level. In the group of classic CLN2 (72 probands), two common mutations were found: an intronic 3556G-->C transversion in the invariant AG of 3' splice junction in 55% of probands, and a nonsense mutation 3670C-->T in 30% of probands. Classic late-infantile onset (2-4 years) was found in 68 of 72 (95%) cases, whereas juvenile onset (> 4 years) occurred only in 4 of 72 (5%) cases. All probands had deficiency of tripeptidyl-peptidase I (TPP1) activity and, at the EM level, curvilinear profiles. Ten probands with late-infantile onset did not show mutations in the CLN2 gene, had normal TPP1 activity, and at the EM level had mixed profiles. Further studies are in progress to identify genetic defect(s) in these subjects. The CLN3 group (40 probands) was divided into two categories: classic or typical presentation, and delayed classic or atypical presentation. All CLN3 patients had onset of symptoms after 4 years of age. In 40 probands, the 1.02-kb common deletion was found in one or two alleles of the CLN3 gene. Homozygotes for the common CLN3 deletion showed the classic phenotype. The phenotype in compound heterozygotes was either the classic or the delayed classic or atypical form. Thus, our study indicates that some mutations in the CLN1 and CLN2 genes may be associated with juvenile onset of the disease process and a more benign clinical course. Interfamilial and intrafamilial variations also were found, especially in the speed of becoming blind and neurologically disabled.

A novel Drosophila alkaline phosphatase specific to the ellipsoid body of the adult brain and the lower Malpighian (renal) tubule.

Two independent Drosophila melanogaster P(GAL4) enhancer-trap lines revealed identical GAL4-directed expression patterns in the ellipsoid body of the brain and in the Malpighian (renal) tubules in the abdomen. Both P-element insertions mapped to the same chromosomal site (100B2). The genomic locus, as characterized by plasmid rescue of flanking DNA, restriction mapping, and DNA sequencing, revealed the two P(GAL4) elements to be inserted in opposite orientations, only 46 bp apart. Three genes flanking the insertions have been identified. Calcineurin A1 (previously mapped to 21E-F) lies to one side, and two very closely linked genes lie to the other. The nearer encodes Aph-4, the first Drosophila alkaline phosphatase gene to be identified; the more distant gene [l(3)96601] is novel, with a head-elevated expression, and with distant similarity to transcription regulatory elements. Both in situ hybridization with Aph-4 probes and direct histochemical determination of alkaline phosphatase activity precisely matches the enhancer-trap pattern reported by the original lines. Although the P-element insertions are not recessive lethals, they display tubule phenotypes in both heterozygotes and homozygotes. Rates of fluid secretion in tubules from c507 homozygotes are reduced, both basally, and after stimulation by CAP(2b), cAMP, or Drosophila leucokinin. The P-element insertions also disrupt the expression of Aph-4, causing misexpression in the tubule main segment. This disruption extends to tubule pigmentation, with c507 homozygotes displaying white-like transparent main segments. These results suggest that Aph-4, while possessing a very narrow range of expression, nonetheless plays an important role in epithelial function.

Tumour suppressor gene mutations in humans and mice: parallels and contrasts.

Tumour suppressor genes prevent cancer development. They can be identified by studying humans, but a full understanding of the mechanisms of their action requires the production of animal models. Mice with mutations in tumour suppressor genes can be produced by gene targeting. The phenotypic consequences of tumour suppressor gene mutations in mice and humans show parallels and contrasts, and both can contribute to the elucidation of disease processes.

Cystinuria subtype and the risk of nephrolithiasis

Cystinuria patients may be classified into several subgroups based on the urinary phenotype of heterozygotes. However, the relative risk for nephrolithiasis and the prevalence of SLC3A1 mutations in these subgroups are unknown. Urinary cystine excretion, age at onset of nephrolithiasis and nature of SLC3A1 mutations were assessed prospectively in 23 cystinuria patients identified primarily through the Quebec Newborn Screening Program. Probands were classified as to cystinuria subtype on the basis of parental urinary cystine excretion. For classical Type I/I cystinuria, both parents excrete cystine in the normal range and probands carry two mutations of the SLC3A1 gene in nearly every case. Between ages 1 to 7 years, mean cystine excretion was high (4566 +/- 480 microns cystine/g creatinine) and exceeded the theoretic threshold for solubility on 70% of visits. Four of eight Type I/I patients began forming stones in the first decade. Type I/III patients (N = 12) excreted less cystine (1544 +/- 163 mumol cystine/g creatinine), exceeded the threshold of urinary cystine solubility less frequently (22% of visits) and had no nephrolithiasis in the first decade; one formed a stone at age 16 years. Only one SLC3A1 mutation was identified in this group. Two Type II/N cystinuria children were identified. In these families, the same level of relatively high excretion (> 600 mumol cystine/g creatinine) was noted in two or three generations, but no SLC3A1 mutations were identified. Classical recessive Type I/I cystinuria is genetically and phenotypically distinct from the other subtypes (Type I/III and Type II/N) identified in our population.

Ectopic c-kit Expression Affects the Fate of Melanocyte Precursors inPatchMutant Embryos

ThePatch(Ph) mutation in the mouse, a deletion that includes the gene for PDGFRα, is a recessive lethal that exhibits a dominant pigment phenotype in heterozygotes. To assess whether thePhmutation acts cell-autonomously or non-autonomously on melanocyte development, we have examined the melanogenic potential of neural crest populations from normal and mutant crest cellsin vitroand the pattern of dispersal and survival of melanocyte precursors (MPs)in vivo.We report that trunk neural crest cells from homozygousPhembryos give rise to pigmented melanocytesin vitroin response to Steel factor (SlF).In vivo,homozygousPhembryos contain a subpopulation of crest-derived cells that express c-kit and tyrosinase-related protein-2 characteristic of MPs. These cells begin to migrate normally on the lateral crest migration pathway, but then fail to disperse in the dermal mesenchyme and subsequently disappear. Although dermal mesenchyme is adversely affected inPhhomozygotes, SlF mRNA expression by the cells of the dermatome is normal inPhembryos when neural crest-derived MPs start to migrate on the lateral pathway. In contrast, mRNA for the SlF receptor, c-kit, was observed to be ectopically expressed in somites and lateral mesenchyme in embryos carrying thePhmutation. Based on this ectopic expression of c-kit inPhmutant embryos, and the observed distribution of SlF protein in normal and mutant embryos, we suggest that competition for limited amounts of SlF localized on the lateral neural crest migration pathway alters melanocyte dispersal and survival.

Interactions of polyhomeotic with Polycomb group genes of Drosophila melanogaster.

The Polycomb (Pc) group genes of Drosophila are negative regulators of homeotic genes, but individual loci have pleiotropic phenotypes. It has been suggested that Pc group genes might form a regulatory hierarchy, or might be members of a multimeric complex that obeys the law of mass action. Recently, it was shown that polyhomeotic (ph) immunoprecipitates in a multimeric complex that includes Pc. Here, we show that duplications of ph suppress homeotic transformations of Pc and Pcl, supporting a mass-action model for Pc group function. We crossed ph alleles to all members of the Polycomb group, and to E(Pc) and Su(z)2 to look for synergistic effects. We observed extragenic noncomplementation between ph503 and Pc, Psc1 and Su(z)2(1) in females, and between ph409 and Sce1, ScmD1 and E(z)1 mutations in males, suggesting that these gene products might interact directly with ph. Males hemizygous for a temperature-sensitive allele, ph2, are lethal when heterozygous with mutants in Asx, Pc, Pcl, Psc, Sce and Scm, and with E(Pc) and Su(z)2. Mutations in trithorax group genes were not able to suppress the lethality of ph2/Y; Psc1/+ males. ph2 was not lethal with extra sex combs, E(z), super sex combs (sxc) or l(4)102EFc heterozygotes, but did cause earlier lethality in embryos homozygous for E(z), sxc and l(4)102EFc. However, ph503 did not enhance homeotic phenotypes of esc heterozygotes derived from homozygous esc- mothers. We examined the embryonic phenotypes of ph2 embryos that were lethal when heterozygous or homozygous for other mutations. Based on this phenotypic analysis, we suggest that ph may perform different functions in conjunction with differing subsets of Pc group genes.

Severity of mutation in the phenylalanine hydroxylase gene influences phenylalanine metabolism in phenylketonuria and hyperphenylalaninaemia heterozygotes.

We examined whether the degree of residual activity from the mutant phenylalanine hydroxylase (PAH) allele affected phenylalanine metabolism in heterozygotes for phenylketonuria (PKU) or non-PKU hyperphenylalaninaemia (HPA). Discriminant analysis was carried out to find the function of fasting plasma concentrations of phenylalanine (PHE) and tyrosine (TYR) that best separated carriers from non-carriers. This function (0.103TYR -0.214-PHECORR -4.499) was subsequently used as the dependent variable, with the in vitro activity of the expressed mutant PAH as the independent variable, in a regression analysis performed on heterozygotes for mutations that had been studied in a eukaryotic cell expression system. This analysis showed a significant correlation (r = 0.40, n = 140, p < 0.001), although there was a wide spread of values within each of the two major groups of carriers and a considerable overlap between the groups. We conclude that the severity of the mutation, as determined by in vitro expression analysis, in the mutant PAH gene is reflected in the biochemical phenotype of heterozygotes. This result emphasizes the relevance of the cell expression system used for establishing the relative severities of most mutations at the PAH locus. Differences in the activities from the carried mutant PAH allele on phenylalanine metabolism in heterozygotes are, however, small compared to the activity from the normal PAH allele and are easily obscured by other factors leading to inter- or intra-individual variation in phenylalanine metabolism. Fasting plasma concentrations of phenylalanine and tyrosine thus can not be used to predict the severity of the carried PAH mutation in individual PKU or HPA heterozygotes.

A Homoallelic Gly317 → Asp Mutation in ALPL Causes the Perinatal (Lethal) Form of Hypophosphatasia in Canadian Mennonites

We have discovered a single homoallelic nucleotide substitution as the putative cause of the perinatal (lethal) form of hypophosphatasia in Canadian Mennonites. Previous linkage and haplotype analysis in this population suggested that a single mutational event was responsible for this autosomal recessive form of hypophosphatasia. The mutation is a guanosine-to-adenosine substitution at nucleotide position 1177 in exon 10 of the tissue nonspecific (liver/bone/kidney) alkaline phosphatase gene. This Gly317-->Asp mutation segregates exclusively with the heterozygote phenotype we previously assigned by biochemical testing (maximum combined lod score of 18.24 at theta = 0.00). This putative disease-causing mutation has not been described in controls nor in other non-Mennonite probands with both lethal and nonlethal forms of hypophosphatasia studied to date. This Gly317-->Asp mutation changes a polar glycine to an acidic aspartate at amino acid position 317 within the highly conserved active site region of the 507-amino-acid polypeptide. Carrier screening for this lethal mutation in our high-risk population is now feasible.

Statistical analysis of a linkage experiment in barley involving quantitative trait loci for height and ear-emergence time and two genetic markers on chromosome 4

The quantitative traits height and ear-emergence date were analyzed in the F2 progeny of a cross between a tall winter barley cultivar (Gerbel) and a short spring barley cultivar (Heriot). The trait distributions were found to be related to the genotypes at two biochemical loci, β-amylase (Bmy1) and water-soluble protein (Wsp3), which are known to lie on the long arm of chromosome 4. Linkages between each trait and the markers were investigated using normal mixture models. The two parental phenotypes and the heterozygote phenotype of Bmy1 were distinguishable so the model could be used directly to estimate linkage between Bmy1 and a quantitative trait locus (QTL) for height (Height). The Gerbel homozygote and heterozygote phenotype of Wsp3 could not be distinguished and the model was adapted accordingly. The proportion of plants requiring vernalization was consistent with control by two independent genes acting epistatically, and a normal mixture model based on a two-gene hypothesis was fitted to the distribution of ear-emergence date to estimate linkage between the marker loci and a QTL for ear-emergence date (Vrn1). The parameters of each model were the recombination fraction between the marker locus and the QTL and the means and standard deviations associated with each QTL genotype; these were estimated by maximum likelihood. The fitted distributions correspond well to those observed and the order of the loci along the chromosome is inferred to be Height - Vrn1 - Bmy1 - Wsp3, with Wsp3 being the most distal.

The Drosophila homolog of the immunoglobulin recombination signal-binding protein regulates peripheral nervous system development

The J κ RBP binds to the immunoglobulin recombination signal sequence flanking the κ-type J segment. We previously Isolated the highly conserved homolog of the J κ RBP gene from D. melanogaster, which is not thought to have immunoglobulin molecules. Using many deficiency mutants and in situ hybridization, we mapped the Drosophila J κ RBP gene in a region containing two recessive lethal mutations, i.e., br26 and br7, which shows the dominant Suppressor of Hairless (Su(H)) phenotype in heterozygotes. All six Su(H) alleles analyzed at the DNA level contained mutations in the Drosophila J κ RBP gene. Since the Su(H) mutation affects peripheral nervous system development, the Drosophila J κ RBP gene product is involved in gene regulation of peripheral nervous system development. The results also imply that the immunoglobulin recombination signal sequence and the target sequence of the Drosophila J κ RBP protein might have a common evolutionary origin.

Genetic analysis of microtubule motor proteins in Drosophila: a mutation at the ncd locus is a dominant enhancer of nod.

The nod (no distributive disjunction) and the ncd (non-claret disjunctional) mutations are both female-specific, recessive meiotic mutations in Drosophila melanogaster. Mutations at either locus show high frequencies of nondisjunction at meiosis I and both have been shown to encode kinesin-like proteins. Unlike the ncd mutation, which affects all chromosome pairs, the nod mutation affects only the disjunction of nonexchange chromosomes. Although both the nod and ncd mutations are fully recessive, females doubly heterozygous for nod and ncd mutations show levels of X and fourth chromosome nondisjunction that are 6- to 35-fold above those observed in control females. Exchange between chromosomes can suppress this effect; thus, only nonexchange chromosomes segregating via the distributive system are sensitive in double heterozygotes. Since the phenotype of double heterozygotes mimics that of the nod mutation, we infer that ncd is a dominant enhancer of nod. Failure of ncd to fully complement nod reveals the chromosome segregation machinery to be dosage sensitive. The probability that the distributive system will fail is enhanced in females simultaneously haploinsufficient at the nod and ncd loci.