Translocation between both members of chromosome pair number 15 causing recurrent abortions

Under-ascertainment of mosaic carriers of balanced homologous acrocentric translocations and isochromosomes

Acrocentric rearrangements are the most common chromosome abnormalities in humans. Carriers of homologous acrocentric rearrangements (Robertsonian translocations (ROBs) between homologous chromosomes and isochromosomes) are at very high risk of having multiple spontaneous abortions and chromosomally abnormal offspring. Parents of fetuses and children with unbalanced homologous acrocentric rearrangements are rarely found to be carriers or mosaic for the same rearrangement. Even though recurrent miscarriages may indicate a carrier parent, carriers are rarely identified. Comparison of non-chromosome 21 homologous rearrangements to rea(21q21q) culled from the literature revealed a 7-fold decrease in the number of mosaic cases among the parents of non-rea(21q21q) offspring. This under-ascertainment in parents may be due to low level mosaicism confined to the gonads, a true biological difference between chromosome 21 rearrangements and other homologous acrocentric rearrangements, or simply to the lack of rigorous clinical investigation of the parental karyotypes to uncover mosaicism. We recommend that polymorphic marker analysis be applied to apparently de novo acrocentric rearrangements to distinguish those resulting from biparental postzygotic formation from those resulting from meiotic formation; the latter of which may indicate a potential carrier parent. Parental chromosomal constitutions could then be screened in a large number of cells and in more than one tissue type to identify mosaicism. Identification of mosaicism allows for accurate genetic counseling and discussion of reproductive options. However, given that mosaicism may be restricted to the gonads, prenatal testing is likely to be desired by the family whether or not mosaicism is found.

Isochromosome 15q of maternal origin in two Prader-Willi syndrome patients previously diagnosed erroneously as cytogenetic deletions

Since our previous report on two Prader-Willi syndrome (PWS) patients with t(15q;15q) (Niikawa and Ishikiriyama; Hum Genet 69:22-27, 1985) was erroneous, we report here new data and a corrected interpretation. Reexamination of the parental origin of their t(15q;15q) using polymorphic DNA markers that are mapped to various regions of 15q documented no molecular deletions at the 15q11-q13 region in either patient. Both patients were homozygous at all loci examined and their haplotypes on 15q coincided with one of those in their respective mothers. These results indicate that the presumed t(15q;15q) in each patient was actually an isochromosome 15q producing maternal uniparental disomy, consistent with genomic imprinting at the PWS locus.

Postzygotic D/D translocation homozygosity associated with recurrent abortions

A Robertsonian translocation involving homologous D chromosomes was found in two cases with a history of recurrent abortions. In the first case the propositus was a 37-year-old phenotypically normal man who had a balanced t(14q14q) translocation. In the second case, a 27-year-old phenotypically normal woman was found to be a balanced t(15q15q) translocation carrier. The recurrent abortions in both cases were probably owing to this translocation.

Prader-Willi Syndrome after age 15 years

Twenty-four patients, all of them over 15 years, with the Prader-Willi syndrome are described. Obesity, often extreme, associated with an insatiable appetite, was their principal handicap and this was made worse by educational subnormality and hypogonadism. Three of the them developed diabetes. Each attended a special school or an adult training centre. Although most of them were of short stature and had scoliosis, 2 were tall but they even more severely mentally retarded than is usually the case. Nine other patients died aged between 3 and 23 years. The most common cause of death was cor pulmonale.

Translocation D/D involving two homologous chromosomes of the pair 15

A translocation between two homologues of chromosomes 15 was identified in a phenotypically normal female with the R-banding technique. The C-banding technique demonstrated an abnormally large band on the translocation chromosome. This finding suggests a possibility that the translocation might be due to breaks in the short arms or to fusion at telomeric ends. The patient had four spontaneous abortions and no normal pregnancy.

The Prader-Willi syndrome with a 15/15 translocation. Case report and review of the literature

A case, diagnosed clinically as the Prader-Willi syndrome, was shown by Giemsa banding, to have a 15/15 chromosome translocation. A review of the literature indicates that such a translocation has only been described once before, in a normal woman, but that chromosme abnormalities in the Prader-Willi syndrome most commonly involve the D group. The significance of this would be clarified by specific chromosome identification in these patients.