Irene A. Uchida

Triploidy and chromosomes

In a total sample of 105 triploid spontaneous abortions and live-born and stillborn infants, the parental origin could be determined in 77%. Dispermy was the most common cause of this abnormality. Among the digynic triploids 69% resulted from retention of the second polar body. Parental ages did not differ from those of the general population except for 10 aneuploid triploids with significantly elevated parental ages. In five sibships, simple aneuploidy in another pregnancy was observed, four of them being potentially viable. Two sisters had triploid conceptions. There were four twin pregnancies, a frequency of one in 26. Only two triploids had an XYY sex chromosome complement, one of which was mosaic with loss of an autosome and the other was a chimera. A frequency of almost 50% of mothers exposed to preconception abdominal radiation is suggestive of an association between radiation and triploidy and requires further investigation.

Molecular studies of parental origin and mosaicism in 45,X conceptuses

SummaryThe present report summarizes molecular studies of parental origin and sex chromosome mosaicism in forty-one 45,X conceptuses, consisting of 29 spontaneous abortions and 12 liveborn individuals with Turner syndrome. Our studies indicate that most 45,X conceptuses have a single, maternally derived X chromosome, regardless of whether the conceptus is liveborn or spontaneously aborted. In studies of mosaicism, our identification of X- and Y-chromosome mosaics among 45,X spontaneous abortions indicates that mosaicism does not ensure survival to term of 45,X fetuses. However, the incidence of sex chromosmome mosaicism is substantially higher in liveborn than in aborted 45,X conceptuses, indicating that the presence of a second cell line increases the likelihood of survival to term.

Trisomy 21 Down syndrome

SummaryThe lymphocyte chromosomes of trisomy 21 Down syndrome patients and their parents in a random series of 374 families were analyzed, the objective being the identification of parental mosaicism. The numbers of parents in whom at least two trisomy 21 cells were detected were seven mothers and three fathers, a frequency of 2.7% of families. Confirmation of mosaicism was by identification of parental transmission of the extra chromosome to the progeny, by repeat chromosome analysis, and/or by the presence of more than one affected child. If to these are added six others in whom only one trisomic cell was detected, but with no other supporting evidence, the frequency could be as high as 4.3%. Differences in parental age at the birth of Down syndrome progeny may be accounted for by differences in frequencies of mosaicism in germ cells and somatic tissue. Mosaicism was found more frequently in the mothers than in the fathers, but more data are required for confirmation of a real difference.

Identification of partial 12 trisomy by quinacrine fluorescence

A patient whose clinical manifestations suggested a diagnosis of Downs syndrome was shown by conventional chromosome analysis to have a normal karyotype. However, examination by fluorescent stains indicated that he had partial trisomy of chromosome No. 12 and deletion of a small portion of chromosome No. 8. His father and sister carried a reciprocal translocation involving these two chromosomes.

Partial 11q trisomy syndrome

SummaryThe syndrome caused by partial trisomy for 11q is reviewed on the basis of a patient of our own and 20 cases (including a stillbirth) from the literature. The main symptoms are presented in Tables 1 and 2. The syndrome can be suspected when, in addition to mental retardation, the following characteristics are present: short nose, long philtrum, micrognathia, retracted lower lip, and micropenis in males. In 15 families, the mother was a balanced translocation carrier and in four the father. The translocation had arisen de novo in two patients. The chromosome number was 46 in 13 affected individuals (including the stillbirth) and 47 in eight. In seven of the latter patients the other translocation chromosome was 22, and in one, chromosome 9. The breakpoints on 11q ranged from 11q121 to 11q232 (Fig. 5). There is no apparent correlation between the length of the trisomic segment and the number or severity of the symptoms (Table 2). This could be explained by assuming that most, if not all, symptoms are caused by trisomy for the Q-dark region distal to 11q232, whereas trisomy for the rest of the 11q up to q121 has few phenotypic effects. These observations support the idea that Q-dark segments, and especially certain hot spots, have a high gene density in contrast with Q-brighter regions.

Identification of Triploid Genome by Fluorescence Microscopy

Fluorescence markers on chromosome numbers 3, 13, and 14 gave cytological evidence of the paternal origin of the extra haploid set in a premature triploid infant with XXY sex chromosome complement. The mother had discontinued the use of oral contraceptives 13 months prior to conception. It is not possible to tell whether the mechanism involved was fertilization by dispermy or by a diploid sperm.

Ring formation of chromosomes Nos. 19 and 20

Two patients with mosaicism for a ring F chromosome are described. Fluorescent stains identified the ring as No. 19 in one patient and No. 20 in the other. Since the majority of cells without the ring

Identification of chromosomal abnormalities by quinacrine-staining technique in patients with normal karyotypes by conventional analysis.

Seventy-two patients with mental retardation and/or congenital anomalies, who were reported to have normal karyotypes with conventional stains, were reanalyzed with the Q-banding technique. Two had an unbalanced translocation, one a paracentric inversion of chromosome No. 16, and one an unusual variant of chromosome No. 21. These results emphasize the importance of using chromosome-banding techniques on a routine basis in order to detect minor chromosomal abnormalities that would otherwise be missed.

Radiation-induced chromosome aberrations in mouse spermatocytes and oocytes.

ICR/Swiss males and females were exposed to 300 R whole-body gamma irradiation. The frequency of aberrations in metaphase I chromosomes recovered from oocytes cultured in vitro was compared with those recovered from spermatocytes irradiated in pachytene and diplotene. The ability of oocytes collected 1 day postirradiation to mature in vitro was not affected, but significantly fewer oocytes cultured 5 days after irradiation matured. The frequency of aberrations in oocytes did not differ from spermatocytes irradiated during diplotene, but significantly more chromosome aberrations were found when pachytene spermatocytes were irradiated. Some variation in the relative frequencies of aberrations was also observed.

Two children with deletion of the long arm of chromosome 4 with breakpoint at band q33

A 10‐year‐old boy with developmental delay, craniofacial dy smorphia, malformations of the hands and feet and a cardiac malformation was found to have a small deletion of the distal region (q33 → qter) of the long arm of a chromosome 4. The clinical findings in this case are compared with those of a 17‐week‐old girl recently found to have the same deletion. Two additional patients with similar small deletions have been described in the literature. The similarity among the cases suggests the possibility of a deletion (4)(q33) syndrome. The major features of the syndrome are similar to those of larger deletions of the long arm of chromosome 4 and include mental and growth retardation, craniofacial dysmorphia including upslanting palpebral fissues, depressed nasal bridge, anteverted nares, abnormally shaped ears and micrognathia, and cardiac defects.