Biomedical subjects
Publications and source records attributed to G Den Dulk.
We present a family in which chromosomally normal parents have had two different structurally abnormal pregnancies. These rearrangements have both been in the mosaic form with a normal cell line. Various mechanisms for this rare situation are discussed.
We describe a boy with the classical Prader Willi syndrome (PWS), clinically, who had a chromosome abnormality not previously described in PWS. The karyotype was 47,XY,+mar, var(15)(p11). The marker was a fragment of 15 from 15pter----q12 and the variant 15p11 was de novo in origin. Overall, this karyotype contains increased 15 heterochromatin and we discuss alteration in the amount of 15 heterochromatin in PWS.
From a total of 1312 diagnostic chorionic villus samplings (CVS) there were 22 which showed discordance between the karyotype of the chorionic villi and that of the fetus. This frequency was some 20-fold higher than that reported at amniocentesis. In the majority of discordant cases, the fetal karyotype was normal while the placental karyotype was mosaic. In four cases, the placental karyotype was non-mosaic (a trisomy 16, a monosomy X, and two tetraploids) while the fetal karyotype was normal. In one case, the placenta was trisomy 18 while the fetus was mosaic. There were two 'false-negative' results where short-term methods showed only normal cells while both long-term cultures of chorionic villi and fetal cells were mosaic, in one 46,XY/47,XXY and in the other 46,XY/47,XY,+21.
Prenatal diagnosis by chorionic biopsy was undertaken between the eighth and 12th weeks of pregnancy in 50 patients at risk of chromosomal or genetic abnormalities. Samples from 45 patients were karyotyped. A DNA analysis for the detection of homozygous beta-thalassaemia was undertaken in five patients. The sample from one patient at risk of haemophilia in the fetus was subjected to DNA analysis after a male fetus was confirmed on karyotyping. Abnormal karyotypes were detected in four fetuses while three had homozygous beta-thalassaemia.
During the course of routine prenatal cytogenetics, a male with 2 different autosomal fragile sites (FS) was detected. The FS were at 9p21 and 12q13 and his sister also had both fragile sites, inherited from an obligate carrier father. He was the father of a foetus with an abnormal chromosome complement 46,XY/47,XY,+frag. The origin of the fragment could not be determined.
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We report a retarded male with an unbalanced karyotype 45,XY,t(8;15) (p23;q12) showing small deletion of chromosome 8(p23 leads to pter) and 15(pter leads to q12). The same chromosome complement was also present in 4 normal family members over 3 generations.