ISSN:1059-7794    

DOI:10.1002/humu.1380010102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractTandem duplication of large regions of DNA, including duplication of whole genes, provides a substrate for genetic evolution. Tandem duplication of smaller regions involving parts of genes is now recognized as a contributor to the mutation spectrum that results in genetic disease. In this review, more than 30 unrelated partial gene duplications that have been implicated in the genesis of human genetic disease are presented and the pathogenic effects and frequency of such duplications are summarized. The mechanisms of duplication formation are analyzed with special emphasis on the molecular details of the nucleotide sequences at the duplication junctions. Evidence to date suggests that duplication may arise from either homologous (Alu—Alu) recombination or nonhomologous recombination, the latter possibly mediated by topoisomerases. For the dystrophin gene, in which most duplications have been identified, these recombination events are intrachromosomal, suggesting that unequal sister chromatid exchange is the major mechanism. © 1992 Wiley‐Liss,

ISSN:1059-7794    

DOI:10.1002/humu.1380010103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractMutations in the human phenylalanine hydroxylase gene producing phenylketonuria or hyperphenylalaninemia have now been identified in many patients from various ethnic groups. These mutations all exhibit a high degree of association with specific restriction fragment‐length polymorphism haplotypes at the PAH locus. About 50 of these mutations are single‐base substitutions, including six nonsense mutations and eight splicing mutations, with the remainder being missense mutations. One splicing mutation results in a 3 amino acid in‐frame insertion. Two or 3 large deletions, 2 single codon deletions, and 2 single base deletions have been found. Twelve of the missense mutations apparently result from the methylation and subsequent deamination of highly mutagenic CpG dinucleotides. Recurrent mutation has been observed at several of these sites, producing associations with different haplotypes in different populations. About half of all missense mutations have been examined by in vitro expression analysis, and a significant correlation has been observed between residual PAH activity and disease phenotype. Since continuing advances in molecular methodologies have dramatically accelerated the rate in which new mutations are being identified and characterized, this register of mutations will be updated periodically. © 1992 Wiley‐L

ISSN:1059-7794    

DOI:10.1002/humu.1380010104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractLaron syndrome is an autosomal recessive condition characterized by resistance to growth hormone. We sought to determine the molecular basis of this condition in an Ecuadorean population with a high incidence of affected individuals. Growth hormone receptor gene sequences from an obligate heterozygote were amplified by the polymerase chain reaction and screened for mutations using denaturing gradient gel electrophoresis. Only exon 6 revealed homo‐ and heteroduplexes on denaturing gradient gels. Sequencing revealed a substitution of guanine for adenine in the third position of codon 180 that did not change the amino acid encoded. Sequencing of the exon 6—exon 7 splice junction from RNA‐polymerase chain reaction amplified cellular RNA of an affected individual revealed that the substitution activates a 5′ splice site 24 nucleotides upstream from the normal exon 6—intron 6 boundary. Splicing in two probands' lymphoblasts occurred virtually exclusively at the abnormal 5′ splice site created by the codon 180 substitution. Exon 6 sequences from 38 patients and 47 relatives were amplified and analyzed by sequencing or dot‐blot hybridization with allele‐specific oligonucleotides. The substitution was detected in 74 of 76 Laron syndrome patients' GH‐receptor alleles. All 26 parents and 12 of 21 unaffected siblings were heterozygous for this mutation. It was absent in 61 unrelated unaffected control individuals. We conclude that the codon 180 nucleotide substitution probably causes Laron syndrome as translation of the observed, abnormally spliced growth hormone receptor transcript would lead to the synthesis of a receptor protein with an 8 amino acid deletion from the extracellular domain. © 19

ISSN:1059-7794    

DOI:10.1002/humu.1380010105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe mutation causing juvenile Tay‐Sachs disease (TSD) in two sibs of Lebanese‐Maronite origin is described. An mRNA‐containing extract of cultured fibroblasts obtained from one of the probands was used as a template to amplify the coding sequence of the hexoaminidase A (Hex A) α‐subunit. Sequencing of amplified cDNA fragments revealed a single alteration, guanine to adenine at nt 749 creating a G250D mutation. The mutation introduces a new recognition site for the restriction enzymeEcoRV, permitting identification of heterozygotes for this allele following PCR amplification andEcoRV digestion of exon 7 sequences from genomic DNA templates. In order to test the effect of this substitution, an in vitro mutagenized cDNA construct was introduced into a mammalian expression vector and transfected into monkey Cos‐1 cells separately or along with a β‐cDNA expression vector. When the mutant α‐cDNA was the only gene introduced into COS cells no enzymatic activity above endogenous COS cell activity was detected. Cotransfection of normal α‐cDNA and β‐cDNA followed by immunoprecipitation of human Hex A resulted in 20‐fold increase in the ratio between positive and negative (mock transfection) control values. This allowed the detection of some residual activity (12% of the positive control) when the mutant α‐cDNA replaced its wild‐type counterpart. The predicted protein environment in which the mutation occurs is compared to that of the adult‐onset Tay‐Sachs disease mutation caused by a Gly269→ Ser substitution in exon 7. We suggest that the more severe clinical phenotype linked to the Gly250→ Asp mutation may be explained by the less conservative substitution of the large, charged aspartate residue as compared to the small neutral serine, and the placement of the Gly250in a hydrophobic section

ISSN:1059-7794    

DOI:10.1002/humu.1380010106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWe describe three HEXA mutations associated with infantile Tay‐Sachs disease (TSD) in three unrelated nonconsanguineous Chinese families. Novel mutations were found in two of these families. The third is a previously reported mutation (G→A transition at nt 1444) (Nakano et al., 1988). Direct sequencing of PCR products identified a novel insertion of an A after nt 547 in family 1. This change generates an early termination codon 6 bp downstream from the insertion site. Allele‐specific oligonucleotide hybridization confirmed homozygosity in the proband. Single strand conformational polymorphism analysis and direct sequencing of amplified exon 13 revealed a T→C transition at nt 1453 with the corresponding amino acid substitution W485R in the second family. This mutation creates an Fnu4HI restriction site. The proband is homozygous for this allele. When the site‐specific mutagenized αcDNA carrying the T→C transition at nt 1453 was expressed in COS 1 cells hexosaminidase S activity was not detectable above background. A G→A transition at nt 1444 (exon 13) corresponding to the E482K substitution was found in the third family. This mutation occurs at a CpG dinucleotide. It has been reported in an Italian TSD proband and causes defective intracellular transport of the α‐subunit from the rough endoplasmic reticulum to the Golgi apparatus. © 19

ISSN:1059-7794    

DOI:10.1002/humu.1380010107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWe have determined that a man, ascertained because he fathered a child with lethal osteogenesis imperfecta (OI) with each of two partners, is mosaic in both his germline and somatic tissues for a mutation in the COL1A2 gene which encodes the proα2(I) chain of type I procollagen. His dermal fibroblasts were previously shown to synthesize a population of cysteine‐containing α2(I) chains that were posttranslationally overmodified. DNA sequence analysis of COL1A2 cDNAs demonstrated that the cysteine‐containing chain resulted from a point mutation (G to T) in the first position of the codon for the glycine at residue 472 of the triple helical domain. Genomic DNA from the one available affected infant contained the mutant and normal COL1A2 alleles in equal proportion. Examination of DNA from several tissues of the father showed that the mutant allele was present in approximately 40% of his sperm, 80% of his lymphocytes, and nearly 100% of his dermal fibroblasts. Despite the high level of mosaicism detected in somatic tissues, the only phenotypic manifestation of OI in the proband was that he was shorter than his unaffected male relatives and had mild dentinogenesis imperfecta. Thermal stability of type I collagen molecules containing the substitution was decreased, but to a lesser extent than for a nonlethal cysteine for glycine substitution at residue 259 of α2(I), indicating that this measure of molecular stability may be of limited use in explaining the pathogenesis of osteogenesis imperfecta. © 1992 Wiley‐

ISSN:1059-7794    

DOI:10.1002/humu.1380010108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractA single base mismatch was detected by a chemical cleavage method in heteroduplexes formed between patient mRNA and a control collagen α2(I) cDNA probe in a case of osteogenesis imperfecta type II. The region of the mRNA mismatch was amplified using the polymerase chain reaction, cloned and sequenced. A heterozygous point mutation of G to C at base pair 1,774 of the collagen α2(I) mRNA resulted in the substitution of glycine with arginine at amino acid position 457 of the helix. Type I collagen of α1(I)‐ and α2(I)‐chains from the patient migrated slowly on electrophoresis due to increased levels of posttranslational modification of lysine. The parents' fibroblast collagen did not contain the mRNA mismatch and the collagens showed normal electrophoretic behaviour. Two‐dimensional electrophoresis of the CNBr peptides from the patient's collagen confirmed the excessive posttranslational modification of the α1(I)‐ and α2(I)‐chains in the CNBr peptides N‐terminal to the mutation due to disruption of the obligatory Gly‐X‐Y triplet repeat of the helix. The mutation led to reduced procollagen secretion and helix destabilization as evidenced by a decreased thermal stability. These data lend further support to the accumulating evidence that type I collagen α2(I) glycine substitution mutations result in the same spectrum of clinical severity as those in the α1(I)‐chain. The disruptive effect of the glycine mutations seems to be largely dependent on the nature of the substituted amino acid, the position in the α‐chain of the mutation, and the nature of the local surrounding amino acid sequence, rather than whether the mutation resides in the α1(I)‐ or α2(

ISSN:1059-7794    

DOI:10.1002/humu.1380010109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWe have developed a strategy for the complete detection of point mutations, small insertions and deletions by chemical cleavage based on the methodology of Cotton et al. (1988). The technique was extended by the development of a nonisotopic cleavage product detection system using silver staining after gel electrophoresis. The complete mutation detection was achieved by use of mutant and wild‐type DNAs in equimolar quantities in duplex formation, thus any mismatches that are resistant to chemical cleavage (e.g., some T·G mismatches) are easily detected by cleavage of the complementary heteroduplex (e.g., A·C mismatch). With such a strategy mutant DNAs can be screened for mutations and polymorphisms. The advantages of complete unlabeled mutation detection are considerable. © 1992 Wiley‐Lis

ISSN:1059-7794    

DOI:10.1002/humu.1380010110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

ISSN:1059-7794    

DOI:10.1002/humu.1380010111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY