No abstract

A 30-month-old boy with mental retardation, hypotonia, joint hyperlaxity, Brushfield spots, open mouth, distal axial triradius t", and ulnar loops on both forefingers was found to have a 47,XY, + psu idic(21)(q22.1).ish psu idic(21)(q22.1)(D13Z1/D21Z1 + + ,ETS2-) karyotype. The patient's phenotype, with only some Down's syndrome (DS) features, is probably related to his disomy for most or all of the critical region 21q22.2 q22.3 and agrees with the current notion that certain DS features may also result from 21q proximal duplications. The phenotypical comparison with 2 other patients with a similar extra idic(21) reveals some discrepancies, which may be related to the inherent clinical variability of similar imbalances: yet, a real difference between the tetrasomic segments cannot be excluded. Noticeably, all 3 patients with 21q proximal tetrasomy did not have cardiac defect and exhibited none or just one out of the five other DS phenotypic features attributed to a single gene or cluster on distal 21q22.

No abstract

A 12-year-old patient with Turner syndrome was found to have a complex mosaicism for a microchromosome (MC) and a psu dic(Y)(q11). The MC was smaller than Yp, appeared pale in G, C and late replicating bands, had a pair of small centromeric dots, was associated with other chromosomes in most metaphases, and was rather stable both in size and during mitosis. The psu dic(Y) was Cd-positive only at the active centromere, had two pericentromeric heterochromatic regions, and lacked the Yq12 band. No cells with both abnormal chromosomes were found. To evaluate the association of the MC with all ordinary chromosomes, 857 G-banded cells with the marker were screened. The MC was considered as "associated" whenever the distance between it and other chromosome(s) was equal to, or smaller than, 18p. Out of 848 associations registered, 489 (57.7%) were centromeric, 202 (23.8%) telomeric, and 157 (18.5%) interstitial; i.e., centromeric associations were overrepresented (P < 0.001) and showed a random distribution, except for an excessive involvement of chromosome 8. This association pattern, also exhibited by two similar MCs in human beings, the minute Y of a marsupial and certain B chromosomes in plants, probably reflects the Rabl orientation of chromosomes in interphase.

Single cell chromosome rearrangements (SCCR) are incidental findings in cell cultures. Nevertheless, some authors have implicated them in habitual abortion. Ninety individuals classified in four groups were prospectively studied: A) individuals with spontaneous abortions, malformed children or molar pregnancies (N = 36); B) azoospermic males (N = 14); C) individuals with one or more children with either de novo or inherited, constitutional, chromosome abnormalities (N = 26), and D) individuals with healthy children and no reproductive failure (control group, N = 14). Lymphocyte chromosome preparations were stained for GTG bands, and 50-100 metaphases were scored per individual. The rearrangements observed were translocations, deletions, duplications, isochromosomes, rings, fragments and markers. Thirty-four individuals (21 males, 13 females) had a range of 1-5 SCCR. Four had rearrangements only of chromosomes 7 and 14. SCCR frequency (with the exception of rearrangements involving chromosomes 7 and 14) was 0.0063, while that of rearrangements between chromosomes 7 and 14 was 0.0010. Statistical intergroup comparisons (c2 with Yates correction) did not show significant differences. Hence, the occurrence of SCCR in our sample was found to be independent of ascertainment mode and sex.
Rearranjos cromossômicos de célula única (SCCR) são achados incidentais em culturas de células. Não obstante, alguns autores os têm relacionado com o abortamento habitual. Noventa indivíduos classificados em 4 grupos foram estudados prospectivamente: A) indivíduos com abortamentos espontâneos, filhos malformados ou gravidezes molares (N = 36); B) homens azoospérmicos (N = 14); C) indivíduos com um ou mais filhos com anormalidades cromosômicas de novo ou herdadas (N = 26) e D) indivíduos sem problemas reprodutivos e com filhos saudáveis (grupo controle, N = 14). As preparações de cromossomos de linfócitos foram coradas para bandamento GTG e 50-100 metáfases foram avaliadas por indivíduo. Os rearranjos observados foram translocações, deleções, duplicações, isocromossomos, anéis, fragmentos e marcadores. Trinta e quatro indivíduos (21 homens e 13 mulheres) tiveram de 1 a 5 SCCR. Quatro tiveram rearranjos apenas dos cromossomos 7 e 14. A freqüência de SCCR (com exceção dos rearranjos envolvendo os cromossomos 7 e 14) foi de 0,0063, enquanto que para os rearranjos entre os cromossomos 7 e 14 foi 0,0010. Comparações estatísticas intergrupo (c2 com correção de Yates) não mostraram diferenças significativas. Assim, a ocorrência de SCCR em nossa amostra mostrou-se independente do modo de averiguação e do sexo