Search

Reciprocal translocations produce imbalances by three types of disjunction which are, in decreasing frequency, adjacent 1, 3:1, and adjacent 2. Adjacent 1 disjunction produces duplication deficiencies of inverse topography to those of adjacent 2. The imbalanced chromosome segments in one of these types are balanced in the other. The disjunction 3:1 produces pure trisomies and monosomies. The following situations predispose to adjacent 2 disjunction: translocations between the long arms of two acrocentric chromosomes or between one of these and that of a No 9 chromosome; centric segments, either short or carrying a heterochromatic zone (9qh); a balanced translocation in the mother. The factors predisposing to the disjunction adjacent 2 operate by selection, or directly on the meiotic configuration. Some of them (shortness of the interstitial segment, shortness of the short arms of translocation chromosomes) act in both these ways. Their influence is probably responsible for the repetitive and exclusive character of this disjunction. The conditions for the occurrence of the 3:1 disjunctions seem less strict than those for adjacent 2, although they should be of the same nature (involvement of acrocentrics or a chromosome 9 in the translocation, maternal origin). [ABSTRACT FROM PUBLISHER]

Five members of a family with a balanced insertion (1;5)(q32;q11q22) are presented. The daughter of one of them shows multiple malformations and a partial trisomy for the long arms of chromosome No. 5 (5q11 to 5q22 segment) resulting from a 'aneusomie de recombinaison' in her mother. The propositus' karyotype is 46,XX,rec(1;5)ins (1;5)(q32;q11q22). This case is the first reported example of an insertion between two chromosomes followed by 'aneusomie de recombinaison'. It also is the first reported case of trisomy invovling the long arms of chromosome No. 5. [ABSTRACT FROM PUBLISHER]