Familial balanced translocation 4p+/17q- as a suggested cause of primary trisomy-21 Down's syndrome

Cytogenetic analysis of sperm from a male heterozygous for a 13;14 Robertsonian translocation

Cytogenetic analysis of 121 sperm from a man heterozygous for a t(13;14) Robertsonian translocation was performed using the technique of in vitro penetration of hamster eggs. The frequency of sperm that were chromosomally unbalanced with respect to the translocation was 27%. The frequency of chromosomally normal (36%) and balanced (38%) complements was approximately equal, as theoretically expected. There was no evidence for an interchromosomal effect since the frequency of numerical chromosomal abnormalities (2.5%) and structural chromosomal abnormalities (10.7%)--both unrelated to the translocation--were within the normal range of control donors. The ratio of X- and Y-chromosome bearing sperm was equal, and there was no evidence for preferential segregation of the X chromosome with the translocation.

Human sperm chromosome studies in a reciprocal translocation t(2;5)

Sperm chromosome complements have been studied in a man heterozygous for a reciprocal translocation t(2;5)(p11;q15). Human sperm chromosomes were obtained after fertilization of zona-free hamster eggs. A total of 75 human sperm metaphases were analysed. On the complements studied, 59 (78.6%) resulted from a 2:2 segregation and 16 (21.3%) from a 3:1 segregation, 4:0 segregation was not observed. Our results indicate that at least 36% of sperm complements were unbalanced with respect to the translocation. The frequency of other chromosome anomalies unrelated to the translocation was 16%.

Cytogenetics of human sperm: meiotic segregation in two translocation carriers

Meiotic segregation products were studied in sperm from two men heterozygous for the reciprocal translocations t(8;15)(p22;q21) and t(3;16)(p23;q24). A total of 226 and 201 sperm complements, respectively, were analyzed. In each translocation, 63% of complements were unbalanced, and alternate and adjacent 1 percentages were similar. The 3:1 segregation frequencies produced by the two translocations were 3.5% and 5.0%.

Chromosomal abnormalities in human sperm

The ability to analyze human sperm chromosome complements after penetration of zona pellucida-free hamster eggs provides the first opportunity to study the frequency and type of chromosomal abnormalities in human gametes. Two large-scale studies have provided information on normal men. We have studied 1,426 sperm complements from 45 normal men and found an abnormality rate of 8.9%. Brandriff et al. (5) found 8.1% abnormal complements in 909 sperm from 4 men. The distribution of numerical and structural abnormalities was markedly dissimilar in the 2 studies. The frequency of aneuploidy was 5% in our sample and only 1.6% in Brandriff's, perhaps reflecting individual variability among donors. The frequency of 24,YY sperm was low: 0/1,426 and 1/909. This suggests that the estimates of nondisjunction based on fluorescent Y body data (1% to 5%) are not accurate. We have also studied men at increased risk of sperm chromosomal abnormalities. The frequency of chromosomally unbalanced sperm in 6 men heterozygous for structural abnormalities varied dramatically: 77% for t11;22, 32% for t6;14, 19% for t5;18, 13% for t14;21, and 0% for inv 3 and 7. We have also studied 13 cancer patients before and after radiotherapy and demonstrated a significant dose-dependent increase of sperm chromosome abnormalities (numerical and structural) 36 months after radiation treatment.

Chromosome abnormality in couples with histories of multiple abortions. The outcome of pregnancies subsequent to ascertainment and a study of familial translocation carriers

A series of couples with histories of recurrent abortions and in whom one partner had been shown to have a major chromosomal anomaly were investigated with respect to the karyotypes of conceptions subsequent to ascertainment. The reproductive histories of translocation carriers amongst relatives were also studied. Results were compatible with previous reports of the behaviour of translocation chromosomes at meiosis with an additional previously undescribed outcome as a result of a maternal 13/14 Robertsonian translocation.

Occurrence of sex chromosome mosaicism and translocation Down's syndrome in the same family

The proband in this family has translocation Down's Syndrome 46,XX,t(14;21)(p11;q11), and this translocation was present in other family members. Sex chromosome mosaicism was demonstrated in three generations of the family, providing another example of familial mosaicism. There was also excessive foetal wastage in different family members. It was not possible to assign the common aetiological factor to account for these various abnormalities. Dermatoglyphic studies showed dominant inheritance of finger-tip arch patterns in one branch of the family.

A case of Turner's syndrome with familial balanced translocation t(1;2)(q32;q21)mat

The first case of Turner's syndrome with the familial translocation not involving the X chromosome is described. The patient had a number of clinical signs of Turner's syndrome and her karyotype was 45,X,t(1;2)(q32;q2)mat. Though it is speculated that the altered structure of a chromosome may influence meiotic disjunction of a non-homologous chromosome, our case suggests that there may be no relationship between the two chromosomal abnormalities.