Intranuclear inclusions and neuritic aggregates in transgenic mice expressing a mutant N-terminal fragment of huntingtin [published erratum appears in Hum Mol Genet 1999 May;8(5):943]

Huntington's disease (HD) is an inherited, neurodegenerative disordercaused by the expansion of a glutamine repeat in the N-terminus of thehuntingtin protein. To gain insight into the pathogenesis of HD, wegenerated transgenic mice that express a cDNA encoding an N-terminalfragment (171 amino acids) of huntingtin with 82, 44 or 18 glutamines. Miceexpressing relatively low steady-state levels of N171 huntingtin with 82glutamine repeats (N171-82Q) develop behavioral abnormalities, includingloss of coordination, tremors, hypokinesis and abnormal gait, before dyingprematurely. In mice exhibiting these abnormalities, diffuse nuclearlabeling, intranuclear inclusions and neuritic aggregates, allimmunoreactive with an antibody to the N-terminus (amino acids 1-17) ofhuntingtin (AP194), were found in multiple populations of neurons. None ofthese behavioral or pathological phenotypes were seen in mice expressingN171-18Q. These findings are consistent with the idea that N-terminalfragments of huntingtin with a repeat expansion are toxic to neurons, andthat N-terminal fragments are prone to form both intranuclear inclusionsand neuritic aggregates.     

Genetics of multiple sclerosis [published erratum appears in Hum Mol Genet 1997 Nov;6(12):2189]

Multiple Sclerosis (MS) is a common chronic central nervous system disease in young adults. Relative familial risk appears to be determined largely by genes while population risk is strongly influenced by environmental factors. This is supported by genetic epidemiological studies which also suggest an oligogenic inheritance of susceptibility. The HLA DRB1*1501, DQA1*0102, DQB1 0602 haplotype is associated with the disease but HLA contributes only modestly to overall susceptibility. The results of three genomic searches are concordant with the genetic epidemiology and imply a number of genes with interacting effects will be found. Importantly, no single region has been identified with a major influence on familial risk.      

Genetic heterogeneity in familial hyperinsulinism [published erratum appears in Hum Mol Genet 1998 Sep;7(9):1527]

Familial hyperinsulinism (HI) is a disorder characterized by dysregulation of insulin secretion and profound hypoglycemia. Mutations in both the Kir6.2 and sulfonylurea receptor (SUR1) genes have been associated with the autosomal recessive form of this disorder. In this study, the spectrum and frequency of SUR1 mutations in HI and their significance to clinical manifestations of the disease were investigated by screening 45 HI probands of various ethnic origins for mutations in the SUR1 gene. Single-strand conformation polymorphism (SSCP) and nucleotide sequence analyses of genomic DNA revealed a total of 17 novel and three previously described mutations in SUR1 . The novel mutations comprised one nonsense and 10 missense mutations, two deletions, three mutations in consensus splice-site sequences and an in- frame insertion of six nucleotides. One mutation occurred in the first nucleotide binding domain (NBF-1) of the SUR1 molecule and another eight mutations were located in the second nucleotide binding domain (NBF-2), including two at highly conserved amino acid residues within the Walker A sequence motif. The majority of the remaining mutations was distributed throughout the three putative transmembrane domains of the SUR1 protein. With the exception of the 3993-9G-->A mutation, which was detected on 4.5% (4/88) disease chromosomes, allelic frequencies for the identified mutations varied between 1.1 and 2.3% for HI chromosomes, indicating that each mutation was rare within the patient cohort. The clinical manifestations of HI in those patients homozygous for mutations in the SUR1 gene are described. In contrast with the allelic homogeneity of HI previously described in Ashkenazi Jewish patients, these findings suggest that a large degree of allelic heterogeneity at the SUR1 locus exists in non-Ashkenazi HI patients. These data have important implications for genetic counseling and prenatal diagnosis of HI, and also provide a basis to further elucidate the molecular mechanisms underlying the pathophysiology of this disease.      

Analysis of molecular variance (AMOVA) of Y-chromosome-specific microsatellites in two closely related human populations [published erratum appears in Hum Mol Genet 1997 May;6(5):828]

The analysis of seven Y-chromosome-specific microsatellite loci revealed a high level of polymorphism in two closely related human populations (Dutch, n = 89, and German, n = 70). Four of these loci were found to generate at least 77 different haplotypes, only 15 of which were shared by the two populations. These results demonstrate that highly informative PCR-based DNA typing of the Y chromosome is now feasible. Assuming a stepwise mutation model, a network comprising all minimum spanning evolutionary trees connecting the haplotypes was constructed. Analysis of molecular variance based upon this network indicated that the within-population heterogeneity with respect to haplotype descent was significantly smaller than the between-population heterogeneity, suggesting that males were more closely related to males from their own population as opposed to males from the other population. These findings suggest that Y-chromosomal microsatellites might be very useful not only for forensic purposes but also in association studies of multifactorial traits, allowing the characterization of the level of genetic distinctiveness of supposedly inbred or isolated populations and discrimination even between closely related populations.      

Analysis of germline mutation spectra at the Huntington's disease locus supports a mitotic [correction of amitotic] mutation mechanism [published erratum appears in Hum Mol Genet 1999 Apr;8(4):717]

Trinucleotide repeat disease alleles can undergo 'dynamic' mutations in which repeat number may change when a gene is transmitted from parent to offspring. By typing >3500 sperm, we determined the size distribution of Huntington's disease (HD) germline mutations produced by 26 individuals from the Venezuelan cohort with CAG/CTG repeat numbers ranging from 37 to 62. Both the mutation frequency and mean change in allele size increased with increasing somatic repeat number. The mutation frequencies averaged 82% and, for individuals with at least 50 repeats, 98%. The extraordinarily high mutation frequency levels are most consistent with a mutation process that occurs throughout germline mitotic divisions, rather than resulting from a single meiotic event. In several cases, the mean change in repeat number differed significantly among individuals with similar somatic allele sizes. This individual variation could not be attributed to age in a simple way or to ' cis ' sequences, suggesting the influence of genetic background or other factors. A familial effect is suggested in one family where both the father and son gave highly unusual spectra compared with other individuals matched for age and repeat number. A statistical model based on incomplete processing of Okazaki fragments during DNA replication was found to provide an excellent fit to the data but variation in parameter values among individuals suggests that the molecular mechanism might be more complex.      

Association between atopic asthma and a coding variant of Fc epsilon RI beta in a Japanese population [published erratum appears in Hum Mol Genet 1996 Dec;5(12):2068]

A genetic association study was performed with coding variants of Fc epsilon RI beta in relation to atopic and non-atopic asthma in a Japanese population (n = 400). A coding variant of Gly237Glu in exon 7 of Fc epsilon RI beta gene showed association with atopic asthma (OR = 3.00, chi 2 = 5.10, p < 0.03), but not with non-atopic asthma; this was seen particularly in childhood asthma (OR = 3.92, chi 2 = 8.66, p < 0.005). This variant is also associated with very high total serum IgE levels (> mean + 3 SD, OR = 8.56, chi 2 = 46.2, p < 0.0001), but not any allergen specific IgE. However, Leu181lle, another variant of Fc epsilon RI beta related to atopy in British and Australian populations, was not found in this Japanese population. These results suggest that variants of Fc epsilon RI beta may be an important genetic cause of the atopic asthma.      

Mapping of a second locus for lamellar ichthyosis to chromosome 2q33-35 [published erratum appears in Hum Mol Genet 1996 Jun;5(6):862-3]

Lamellar ichthyosis (LI) is an inherited autosomal recessive disorder of cornification. It was recently demonstrated to result from deleterious mutations in the transglutaminase 1 (TGM1) gene. However, the disease was shown to be genetically heterogeneous, since some families were found to be unlinked to TGM1. Homozygosity mapping on three consanguinous families originating from Morocco shows (i) absence of linkage with TGM1 and other regions of the genome containing genes involved in cornification, and (ii) location of a second disease- causing gene on chromosome 2q33-35. A maximum two-point lodscore of 7.60 was obtained with D2S157 for theta = 0. The analysis of recombination events places the gene within a 7-8 cM interval. Additional consanguinous pedigrees were also demonstrated to be unlinked both to TGM1 and to 2q33-35, suggesting the existence of at least a third disease-causing gene.      

Evolution of the human RH (rhesus) blood group genes: a 50 year old prediction (partially) fulfilled [published erratum appears in Hum Mol Genet 1997 Aug;6(8):1390]

Almost exactly 50 years ago, R. A. Fisher and R. Race proposed a model for the evolution of the RH (rhesus) genes in which the less common haplotypes were derived from the commoner ones by recombination, and in which the gene order was D-C-E. No direct-evidence bearing on this model was available then, and has not been until now. Here we present evidence for non-reciprocal intergenic exchange (gene conversion) occurring once in human history to generate the common RHCE allele, Ce. We have also used new polymorphisms to construct haplotypes which suggest that intragenic recombination played a major role in the generation of the less common haplotypes, but only if RHD lies 3' of RHCE, i.e. the order is C-E-D. We provide both genetic and physical evidence supporting this arrangement.      

Mutation of the RET ligand, neurturin, supports multigenic inheritance in Hirschsprung disease [published erratum appears in Hum Mol Genet 1998 Oct;7(11):1831]

Hirschsprung disease (HSCR) is a frequent neurocristopathy characterized by the absence of submucosal and myenteric plexuses in a variable length of the gastrointestinal tract. Pedigrees and segregation analyses suggested the involvement of one or several dominant genes with low penetrance in HSCR. Considering that RET and glial cell line-derived neurotrophic factor (GDNF) mutations have been reported in the disease, we regarded the other RET ligand, neurturin (NTN), as an attractive candidate gene, especially as it shares large homologies with GDNF. Here, we report on the finding of a heterozygous missense NTN mutation in a large non-consanguineous family including four children affected with a severe aganglionosis phenotype extending up to the small intestine. Interestingly, it appears that the NTN mutation reported here is not sufficient to cause HSCR, and this multiplex family also segregates a RET mutation. This cascade of independent and additive genetic events fits well with the multigenic pattern of inheritance expected in HSCR, and further support the role of RET ligands in development of the enteric nervous system.      

Global sequence diversity of BRCA2: analysis of 71 breast cancer families and 95 control individuals of worldwide populations [published erratum appears in Hum Mol Genet 1999 Apr;8(4):717-9]

The aim of this study was to evaluate the prevalence of simple sequencevariation in the BRCA2 gene. To this end, 71 breast and breast-ovariancancer (HBC/HBOC) families along with 95 control individuals from a widerange of ethnicities were analyzed by means of denaturing high- performanceliquid chromatography (DHPLC) and direct sequence analysis. In the coding(10 257 bp) and non-coding (2799 bp) sequences of BRCA2, 82 sequencevariants were identified. Three different, apparently disease-associatedBRCA2 mutations were found in six HBC/HBOC families (8%): two splice sitemutations in introns 5 and 21, and one frameshift mutation in exon 11. Inthe coding region, 53 simple sequence variants were found: 35 missensemutations, one 2 bp deletion (CT) resulting in a stop at codon 3364, onenonsense mutation with a stop at codon 3326, one deletion of a completecodon (AAA) resulting in the loss of leucine, and 15 silent mutations. Inthe non-coding region, 26 polymorphisms were detected. Of the 79 sequencevariants that were not obviously disease-associated, eight were detectedonly in HBC/HBOC families. The remaining 71 variants were identified inboth HBC/HBOC families and control individuals. Sixty three sequencevariants (80%) were specific for a continent. Forty two percent (33 out of79) of the sequence variants were detected exclusively in Africa, thoughonly 13% of the 332 chromosomes screened were of African origin. Our dataindicate that, in BRCA2, simple sequence variation is frequent [in thecoding region 1 in 194 bp (straight theta = 2.2 x 10(-4)), and in thenon-coding region 1 in 108 bp (straight theta = 4.4 x 10(-4)),respectively].     

The gene responsible for autosomal dominant Doyne's honeycomb retinal dystrophy (DHRD) maps to chromosome 2p16 [published erratum appears in Hum Mol Genet 1996 Sep;5(9):1390]

Degeneration in the macula region of the retina is a feature of a heterogeneous group of inherited, progressive disorders, causing blinding visual impairment. Autosomal dominant Doyne's honeycomb retinal dystrophy (DHRD) is characterised by the presence of drusen deposits at the level of Bruch's membrane in the macula and around the edge of the optic nerve head. We have studied 63 members of a large, nine-generation British pedigree by linkage analysis. Two-point analysis showed significant linkage to nine markers on the short arm of chromosome 2, a region overlapping that recently reported to be linked to Malattia leventinese. A maximum lod score (Zmax) of 7.29 (theta = 0.0) was obtained at marker locus D2S2251. Haplotype analysis of recombination events localised the disease to a 5 cM region between marker loci D2S2316 and D2S378. Striking clinical similarities between DHRD and the more common condition age-related macular degeneration (ARMD) suggest that the disease gene at this locus could be considered as the most likely candidate in future studies on ARMD.      

Prevalence of p16 and CDK4 germline mutations in 48 melanoma-prone families in France. The French Familial Melanoma Study Group [published erratum appears in Hum Mol Genet 1998 May;7(5):941]

Germline mutations in the p16 and CDK4 genes have been reported in a subset of melanoma pedigrees, but their prevalence is not well known. We searched for such germline mutations in 48 French melanoma-prone families selected according to two major criteria: families with at least three affected members (n = 20) or families with two affected members, one of them affected before the age of 50 (n = 28), and one additional minor criterion. Sixteen different p16 germline mutations were found in 21 families, while one germline mutation, Arg24His, was detected in the CDK4 gene. The frequency of p16 gene mutation in our sample (44%) is among the highest rates yet reported and the CDK4 mutation is the second mutation detected in this gene worldwide. In summary, our results show frequent involvement of the p16 gene in familial melanoma and confirm the role of the CDK4 gene as a melanoma- predisposing gene.      

Linkage studies of non-syndromic recessive deafness (NSRD) in a family originating from the Mirpur region of Pakistan maps DFNB1 centromeric to D13S175 [published erratum appears in Hum Mol Genet 1996 May;5(5):710]

Autosomal recessive non-syndromal hearing impairment (NSRD) is genetically heterogeneous. Five loci have been identified to date which map to chromosomes 13 (DFNB1), 11 (DFNB2), 17 (DFNB3), 7 (DFNB4) and 14 (DFBN5). We report definite linkage of NSRD to the locus DFNB1 in a single family of 27 families studied of Pakistani origin. Haplotype analysis of markers in the pericentromeric region of chromosome 13q revealed a recombination event which maps DFNB1 proximal to the marker D13S175 and in the vicinity of D13S143.      

Molecular analysis of the SMN and NAIP genes in Spanish spinal muscular atrophy (SMA) families and correlation between number of copies of cBCD541 and SMA phenotype [published erratum appears in Hum Mol Genet 1996 May;5(5):710]

Spinal muscular atrophy is an autosomal recessive disorder which affects about 1 in 10,000 individuals. The three clinical forms of SMA were mapped to the 5q13 region. Three candidate genes have been isolated and shown to be deleted in SMA patients: the Survival Motor Neuron gene (SMN), the Neuronal Apoptosis Inhibitory Protein gene (NAIP) and the XS2G3 cDNA. In this report we present the molecular analysis of the SMN exons 7 and 8 and NAIP exon 5 in 65 Spanish SMA families. NAIP was mostly deleted in type I patients (67.9%) and SMN was deleted in 92.3% of patients with severe and milder forms. Most patients who lacked the NAIP gene also lacked the SMN gene, but we identified one type II patient deleted for NAIP exon 5 but not for SMN exons 7 and 8. Two other patients carried deletions of NAIP exon 5 and SMN exon 7 but retained the SMN exon 8. Three polymorphic variants from the SMN gene, showing changes on the sequence of the centromeric (cBCD541) and telomeric copies of the SMN gene, were found. In addition, we show several genetic rearrangements of the telomeric SMN gene, which include duplication of this gene in one normal chromosome, and putative gene conversion events in affected and normal chromosomes. Altogether these results corroborate the high genetic variability of the SMA region. Finally, we have determined the ratio between the number of centromeric and telomeric copies of the SMN gene in parents of SMA patients, showing that the majority of parents of types II and III patients carried three or more copies of the cBCD541 gene; we suggest a relationship between the number of copies of cBCD541 and the disease phenotype.      

The domain encoded by exon 2 of the survival motor neuron protein mediates nucleic acid binding [published erratum appears in Hum Mol Genet 1998 Oct;7(11):1831]

Spinal muscular atrophy (SMA) is a motor neuron disorder resulting from anterior horn cell death. Survival motor neuron ( SMN ) is the SMA- determining gene and is deleted or gene converted in >95% of SMA patients. The SMN protein has a role in spliceosomal snRNP biogenesis and has therefore been implicated indirectly in general cellular RNA processing due to its unique sub-nuclear localization within structures termed 'gems', which co-localize with spliceosomal factors within coiled bodies. In this report, direct SMN RNA-binding activity, in addition to ssDNA and dsDNA binding is demonstrated. The region of SMN encoded by exon 2 is necessary and sufficient to mediate its nucleic acid-binding activities. This domain is homologous to several nucleic acid-binding factors, including several high mobility group (HMG) proteins. Additionally, previously reported SMN missense mutations isolated from SMA patients demonstrated reduced RNA-binding activity, suggesting that nucleic acid binding is functionally significant.      

Reliability of estimates of diploid human spermatozoa using multicolour fluorescence in-situ hybridization [published erratum appears in Hum Reprod 1997 May;12(5):1118]

Multicolour fluorescence in-situ hybridization (FISH) analysis permits distinction between disomic and diploid spermatozoa. Thus estimates of the frequency of diploid spermatozoa can be obtained for human semen samples. The issue of the accuracy and reliability of these diploidy estimates has been addressed by analysing diploidy frequencies in 10 men using the same sperm sample to estimate diploidy twice-once during two-colour FISH analysis of disomy for chromosomes 1 and 12 and a second independent analysis of three-colour FISH for disomy estimates for chromosomes X and Y (with chromosome 1 used as the autosomal control). A minimum of 10,000 spermatozoa per hybridization per male was counted for a total of over 200,000 spermatozoa analysed. The mean frequency of diploid spermatozoa was 0.13% for the autosomal study and 0.14% for the sex chromosomal study, which were not significantly different. One donor had extremely divergent values of diploidy in the two studies. Analysis of values in the other nine donors demonstrated no significant difference in the two diploidy estimates. These results indicate that the FISH technique is an accurate and reliable method for determining diploid frequencies in human spermatozoa.