A de novo dicentric Y;21 (q11.23;p11) translocation chromosome with one of its two centromeres inactive has provided the opportunity to study the relationship between centromeric inactivation, the organization of alphoid satellite DNA and the distribution of CENP-C. The proband, a male with minor features of Down's syndrome, had a major cell line with 45 chromosomes including a single copy of the translocation chromosome, and a minor one with 46 chromosomes including two copies of the translocation chromosome and hence effectively trisomic for the long arm of chromosome 21. Centromeric activity as defined by the primary constriction was variable: in most cells with a single copy of the Y;21 chromosome, the Y centromere was inactive. In the cells with two copies, one copy had an active Y centromere (chromosome 21 centromere inactive) and the other had an inactive Y centromere (chromosome 21 centromere active). Three different partial deletions of the Y alphoid array were found in skin fibroblasts and one of these was also present in blood. Clones of single cell origin from fibroblast cultures were analysed both for their primary constriction and to characterise their alphoid array. The results indicate that (1) each clone showed a fixed pattern of centromeric activity; (2) the alphoid array size was stable within a clone; and (3) inactivation of the Y centromere was associated with both full-sized and deleted alphoid arrays. Selected clones were analysed with antibodies to CENP-C, and staining was undetectable at both intact and deleted arrays of the inactive Y centromeres. Thus centromeric inactivation appears to be largely an epigenetic event.
The a1 thalassaemia alleles in 501p thalassaemia heterozygotes originating from many parts of the United Arab Emirates (UAE) have been characterised using the allele specific priming technique of the polymerase chain reaction (PCR). The IVSI-5 (G-.C) mutation was found to be present in 66%, while six other alleles occurred at the much lower frequencies of 2% to 8%. These were codon 8/9 (+ G), IVSI-1, 3' end (-25 bp), codon 5 (-CT), IVSII-1 (G-)A), codon 30 (G-+C), and codon 15 (G-A). The mutation types and percentages are compared with other Mediterranean Arab countries and neighbouring areas. It is proposed that IVSI-5 and other Asian Indian mutations were introduced into the UAE by population migration from the region previously known as Baluchistan. These findings should be useful for genetic counselling and the development of a first trimester prenatal diagnosis programme based on direct detection of mutations in the UAE.
The QF-PCR methodology is an efficient cost-effective method of screening for major chromosome aneuploidy, and, for certain referral categories, could be used alone. It also appears to be applicable to patients of different ethnic origins.
We describe an infant girl with an interstitial deletion of chromosome bands 5q33 to 5q35 inherited from a maternal interchromosomal insertion ins(8;5)(p23;q33q35) which was demonstrated by fluorescent in situ hybridization with whole chromosome paints. Physical anomalies included hypertonicity, microcephaly, short neck, apparently low-set ears, micrognathia, camptodactyly, mild rocker bottom feet, and hammer toe. Cardiac anomalies included a large ventricular septal defect, patent ductus arteriosus, pulmonary hypertension and hypoplastic right ventricle. She died at age 3 months.
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