A familial {open_quotes}balanced{close_quotes} 3;9 translocation with cryptic 8q insertion leading to deletion and duplication of 9p23 loci in siblings
- Harvard Medical School, Boston, MA (United States)
A child with phenotypic features of the 9p{sup {minus}} syndrome, including metopic craniosynostosis, small ears, abdominal wall defect, and mental retardation, as well as hypopigmentation, was found to have a cytogenetically balanced 3;9 translocation, with breakpoints at 3p11 and 9p23, inherited from his phenotypically normal father. Molecular analysis showed heterozygous deletion of the TYRP (tyrosinase-related protein) locus, as well as loci D9S157, D9S274, D9S268, and D9S267, in the child but in neither parent. FISH analysis of the proband`s father indicated that loci deleted in his son, including TYRP, were present on neither the der(3) nor the der(9) translocation products but had been inserted into the long arm of chromosome 8. Therefore, the apparent deletion of these loci in the proband was the result of meiotic segregation of the father`s 3;9 translocation chromosomes together with his normal chromosome 8 (not bearing the insertion from 9p23). Neither the deletion of these 9p23 loci from the translocation chromosomes nor their insertion into 8q was detectable by standard chromosome banding techniques. The proband`s sister exhibited speech delay, mild facial dysmorphism, and renal malformation, and her karyotype was 46,XX. Molecular analysis showed that she had inherited normal chromosomes 3 and 9, as well as the chromosome 8 with the insertion of 9p23 material, from her father. This analysis illustrates a new mechanism to explain cases in which an apparently balanced translocation has been transmitted from a normal parent to a child with a phenotypic abnormality: submicroscopic deletion of material from the translocation breakpoint and insertion into a third chromosome in the balanced parent, with meiotic segregation leading to loss of the inserted material in the child. 36 refs., 9 figs., 1 tab.
- OSTI ID:
- 70394
- Journal Information:
- American Journal of Human Genetics, Vol. 56, Issue 1; Other Information: PBD: Jan 1995
- Country of Publication:
- United States
- Language:
- English
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