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Webb, T P; Bundey, S; Thake, A; Todd, J
doi: 10.1136/jmg.23.5.396pmid: 3783615
A population study has been carried out among schoolchildren in the City of Coventry in order to ascertain the frequency of mental retardation associated with the fragile X chromosome. The prevalence of the fragile X mental retardation syndrome in the 11 to 16 year age group (the age of greatest ascertainment) was about 1.0 per 1,000 and therefore indicates that the syndrome is a major cause of mental retardation.
doi: 10.1136/jmg.23.5.400pmid: 3783616
Through a community study of boys requiring special education for the severely mentally retarded, 12 families were ascertained in which the fragile X was found to be segregating. By assiduous follow up of these families, it was found that in only four of them could male transmission be ruled out from the grandparents' or great grandparents' generation and that the segregation ratios are disturbed.
Tuckerman, E; Webb, T; Thake, A
doi: 10.1136/jmg.23.5.407pmid: 3783617
Chromosome analysis, after bromodeoxyuridine incorporation and a sequential Leishman acridine orange staining method previously described, was used to assess the percentage of early or active fragile Xs compared with the overall total in informative cells in 13 heterozygous females. The percentage thus obtained was then used to calculate the percentage of early or active fragile X that would be expected in a culture without bromodeoxyuridine, that is: percentage active fragile X divided by 100 X percentage fra(X) in standard 199 or M culture. Five females were normal and eight of below normal intelligence. In one culture pokeweed mitogen was substituted for phytohaemagglutinin and the percentage of active fragile Xs obtained was compared with that obtained with phytohaemagglutinin. In the same female the effect of addition of fluorodeoxyuridine and methotrexate on the replication ratio of the X was also investigated. R banded and G banded cells from this subject were also scanned for the deletion of Xq27.3----qter.
Wallis, G; Beighton, P; Boyd, C; Mathew, C G
doi: 10.1136/jmg.23.5.411pmid: 3023615
We have analysed six South African families with osteogenesis imperfecta type I using three DNA polymorphisms associated with the pro alpha 2(I) collagen gene. In four of these families linkage of the pro alpha 2(I) gene and the osteogenesis imperfecta phenotype was suggested, whereas in the remaining two families there was a lack of linkage. No distinct correlation could be made between the phenotypic features of the families studied and linkage or lack of linkage to the pro alpha 2(I) gene. Two different haplotypes were found to be associated with the mutant pro alpha 2(I) alleles. These findings suggest that molecular heterogeneity exists within osteogenesis imperfecta type I and that in a significant proportion of cases the defect is linked to the pro alpha 2(I) gene.
Wainwright, B; Farrall, M; Watson, E; Williamson, R
doi: 10.1136/jmg.23.5.417pmid: 3783618
We have used multilocus analysis to exclude the cystic fibrosis locus from six polymorphic DNA markers covering most of chromosome 19. A substantial increase in the confidence for exclusion was obtained using the computer programme LINKAGE compared to analysis of pairwise lod scores. A structured approach to the analysis of linkage to autosomal recessive inherited diseases where the biochemical defect is not known is described.
doi: 10.1136/jmg.23.5.421pmid: 3023616
Recent advances in agarose gel electrophoresis of large DNA fragments raise the possibility of an entirely new approach to mapping mammalian genomes. In this article is discussed the potential of this technology for tackling problems such as construction of linkage maps, identifying chromosome translocation breakpoints, and moving from linked markers to genes causing diseases such as the muscular dystrophies and Huntington's chorea.
Wynne-Davies, R; Hall, C M; Young, I D
doi: 10.1136/jmg.23.5.425pmid: 3783619
This survey reviews the diagnosis (predominantly radiological) of 32 cases of pseudoachondroplasia from 26 kindreds and illustrates the natural history and varying appearance of the disordered bone growth from infancy to adult life. In addition, an attempt has been made to detect phenotypic differences between autosomal dominant and recessive types (excluding isolated cases), analysing 10 kindreds of dominant inheritance (three in the current survey, seven from published reports) and six of recessive inheritance (three in the current survey, three from published reports). There appears to be no clinical or radiographical feature which clearly distinguishes them, but, using height as a criterion of severity, among those with autosomal recessive inheritance there was a disproportionate number of the most severely affected cases and there also appears to be very little intrafamilial variation. It is possible that pseudoachondroplasia can be subdivided into autosomal dominant mild and severe and autosomal recessive mild and severe, but full delineation must await elucidation of the basic defect at biochemical and molecular levels.
Brusnický, J; van Heerden, K M; de Jong, G; Cronjé, A S; Retief, A E
doi: 10.1136/jmg.23.5.435pmid: 3783620
Partial monosomy 10q25.2----qter, detected in a newborn baby with multiple congenital abnormalities, was found to be derived from a balanced maternal translocation t(6;10)(q27;q25.2). The pedigree of six generations of the family is presented. In an extensive cytogenetic study of this family, the chromosome complements of 57 subjects, potentially capable of carrying some form of this translocation, were analysed. A total of 14 male carriers (four obligatory) and 14 female carriers (three obligatory) of this translocation was found. Partial trisomy 10q25.2----qter, associated with severe mental retardation, occurred in nine cases, eight males and one female. Two of these eight males were detected prenatally and subsequently therapeutically aborted. The phenotypes of the family members with partial trisomy 10q25.2----qter are compared to each other and to those reported in publications. No further cases of partial monosomy 10q25.2----qter were encountered. A review of published reports of partial monosomy and partial trisomy 10qter is given. The apparent absence of infertility, the occurrence of many first trimester miscarriages, and the marked sex ratio are discussed.
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