Two cases of pericentric inversion of chromosome 12 are presented, one 46,XX,inv(12)(p13;q11) and the other was also a heterozygotic carrier of the inversion. These inversions were detected among 4035 cytogenetic analyses carried out in patients with psychosomatic retardation and/or malformations (357 with a Down phenotype) and in patients with histories of miscarriages, sterility, or growth failure. In cases studied from a review of the literature together with our own we found that among 3235 cases of Down syndrome there were 7 patients with trisomy 21 and inherited balanced reciprocal translocation involving chromosomes other than pair 21. The frequent participation of some chromosomes in these balanced reciprocal translocations, above all those of group A (1-3), suggests that these and probably other rearrangements could make the segregation of chromosome 21 easier.
A karyotype with six de novo autosomal abnormalities in chromosomes 2,4,9,10,12, and 13 was identified in a 7-year-old boy with mental retardation and other minor malformations. The G- and C-banding techniques revealed an equilibrated translocation between autosomes 2 and 4 and between autosomes 9 and 13. One chromosome 10 has lost genetic material from its short arms, probably because of an interstitial deletion. An unidentified chromosomal fragment has become inserted in the long arms of an autosome 12. The G bands demonstrate that genetic material inserted in the autosome 12 is not the genetic material deleted from the autosome 10. The propositus presents clinical features similar to the reported cases with 10p- syndrome. Nevertheless it is not possible to establish the influence of the genetic material inserted in autosome 12 on the propositus' phenotype.
We studied a family in which three of the members present one chromosome 6 with an isochromatid gap at the band 6q15 level. Studies of the chromosomes by various banding techniques suggested that the secondary constriction represents a stalk from an acrocentric chromosome inserted into 6q15. The possible influence of the abnormal localization is considered.
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