In a family in which a large pericentric inversion of chromosome 7 is segregating, two of the four progeny of inversion heterozygotes show severe psychomotor retardation and have the karyotype 46, XX, rec(7), dup q, inv(7)(p22q32), derived from crossing-over within the inversion. Meiotic analysis in one of the heterozygotes revealed no evidence of inversion loops in well-spread pachytene cells. In approximately 20 % of cells in diakinesis, the presumptive bivalent 7 had only one chiasma. Two alternatives to the reversed loop mode of meiotic pairing of inversions are proposed. Review of the literature supports the view that “small” pericentric inversions have a much better genetic prognosis than “large” pericentric inversions.
A further patient with the ICF syndrome (immunodeficiency, centromeric heterochromatin instability of chromosomes 1, 9 and 16 and facial anomalies) is described. This case is the second to be reported with consanguinity of the parents. This lends support to the theory of autosomal recessive inheritance. The features of the 15 published cases are reviewed. The clinical and cytogenetic characteristics of the syndrome are discussed, and new evidence provided as to the role of centromeres and centric heterochromatin in the production of chromosome aberrations. Correspondence with other authors has made possible a review of the clinical outcome in this condition.
Karyotype analyses made from photomicrographs of 1303 human somatic cells derived mainly from peripheral leucocyte cultures obtained during the investigation of patients for chromosome aberrations, have been re-examined in order to determine the sites and relative frequencies of secondary constrictions. It has been confirmed that the chromosomes showing secondary constrictions most frequently in this material are chromosomes 13, 14, 15, 21 and 22. In these five pairs, a secondary constriction in the short arm separates a terminal mass, the satellite, from the rest of the chromosome arm. Secondary constrictions were also observed at specific sites in other chromosomes, although less frequently. In chromosomes 1, 6, 9 and 17 the constriction peculiar to each appeared in over 20% of the available chromosomes of the respective chromosome pair. Examples of secondary constrictions in these and other chromosomes are illustrated. Our observations provide evidence of at least fifteen sites, where constrictions are visible at a definite point with sufficient frequency to exclude any explanation other than that they are a distinct entity, characteristic for each chromosome. For each of these 15 constrictions, 10 chromosomes have been measured and the distance from the centromere to the constriction determined. The characteristic site of each constriction is indicated in a “normal human idiogram” constructed from chromosome measurements in 10 selected male cells. The value of secondary constrictions in the identification of human chromosomes is discussed, and the importance of recognising their location and variable appearance is stressed in view of the possibility that they may on occasions be interpreted as evidence of chromosome aberration.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.