No abstract

Using the human sperm–hamster oocyte fusion technique and whole chromosome painting, we studied sperm chromosome segregation in a male heterozygous for a complex chromosome rearrangement, 46,XY,–2,+der(2)t(2;11)(q13; q23),–11,+der(11)t(11;22)(q23;q11.2),–22,+der(22)t(2;22)(q13; q11.2). A total of 208 sperm complements were analyzed. The frequency of sperm carrying a normal or a balanced complement was 13.5% (9.62% and 3.85%, respectively). The frequency of unbalanced sperm was 86.5% (64.9% from 3:3 segregation, including 30 different types; 20.7% from 4:2 segregation, including 21 different types; and 0.96% from 5:1 segregation, including 2 different types). The sex ratio, determined in 134 sperm complements, did not differ from the expected 1:1 ratio. The results obtained in this study are compatible with the formation, during the synaptic process, of a complex hexavalent figure involving chromosomes 2, 11, and 22. The behavior and segregation of this complex figure would explain the high frequency (86.5%) of unbalanced complements observed in this carrier.

We have studied the meiotic segregation of a reciprocal translocation t(5;7)(q21;q32) in a male carrier, using the human sperm-hamster oocyte fusion technique and the whole chromosome painting. A total of 296 sperm complements were analysed by dual chromosome painting. The frequencies of alternate, adjacent-1, adjacent-2 and 3:1 segregation were 49.7%, 32.4%, 16.2% and 1.7% respectively. Aneuploidy frequencies for chromosomes not involved in the translocation were determined by FISH on decondensed sperm heads using probes from chromosomes X, Y, 6, 18 and 21. A total of 20 118 spermatozoa was analysed, 10 201 by twocolour FISH (probes for chromosomes 6 and 21) and 9917 by three-colour FISH (probes for chromosomes X, Y, and 18). There was no evidence of an interchromosomal effect, since disomy frequencies were within the range of normal controls.

A complex familial chromosome translocation has been ascertained by combining classical cytogenetics and CISS (chromosomal in situ suppression). Cytogenetic analysis of a chorionic villus sample with G banding showed a 47,XX,-2, +der(2)t(2;22),+der(22)t(2;22) karyotype. Analysis of peripheral blood lymphocytes from the parents by G banding and CISS showed a more complex translocation in the father: 46,XY,-2,-11,-22, +der(2) t(2;11)(q13;q23), +der(11) t(11;22) (q23; qI1.2), +der(22) t(2;22) (ql3;ql1.2).Definitive analysis of cultured amniotic fluid cells showed a double partial trisomy of chromosomes 11 and 22. The couple decided to continue the pregnancy. The fetal karyotype was confirmed at birth. Clinical abnormalities present in our patient were typical of an unbalanced 11;22 translocation. Our findings confirm that chromosome painting techniques allow a better characterisation of complex chromosome rearrangements which may be difficult to detect in G banded karyotypes.