Down syndrome due to a recombination of a chromosome 21 paracentric inversion in 1 of 2 cases with a review of paracentric recombinants
- Wake Forest Univ., Winston-Salem, NC (United States); and others
We recently identified 2 paracentric inversions (PAI) of chromosome 21. Case 1 was identified prenatally and paternally inherited: 46,XY,inv(21)(q21.2q22.13). The outcome is pending. Case 2 was a newborn male infant with clinical features of Down syndrome and an apparent inversion-duplication within chromosome 21. Parental chromosome analysis showed a maternal PAI: 46,XX,inv(21)(q21.2q22.3). The resulting child`s karyotype was: 46,XY,rec(21)(pter{yields}q21.2::q22.3{yields}q21.2::q22.3{yields}pter). Duplication of chromosome region q22.3{yields}qter was confirmed by FISH using a Down syndrome region specific probe (Cambio). Cytologically, the cornerstone of meiotic recombination from a paracentric inversion is the {open_quotes}reverse loop{close_quotes} model. In this model, a crossover event in the inversion loop results in the formation of gametes carrying either a dicentric chromatid, an acentric fragment, a normal chromatid or a chromatid with an inversion. However, a literature review of 326 PAI identified only 2 dicentrics and 15 other recombinants: 1 duplication/deletion; 6 deletions; 8 duplications. A U-type exchange model during meiosis within the inversion loop may best account for duplication/deletion recombinants. In contrast, the recombination in our case 2 would have occurred outside the loop. It is possible that no single explanation for PAI recombination may account for all outcomes. Alternative models of PAI recominational events will be presented. The literature suggests a low risk for prenatal loss due to abnormal PAI recombinants. In our review, viable offspring with recombinant chromosomes occurred in 3.8% of the PAI. Considering the potential for an increased incidence of recombination, prenatal diagnosis for all PAI carriers is warranted.
- OSTI ID:
- 133701
- Report Number(s):
- CONF-941009--
- Journal Information:
- American Journal of Human Genetics, Journal Name: American Journal of Human Genetics Journal Issue: Suppl.3 Vol. 55; ISSN AJHGAG; ISSN 0002-9297
- Country of Publication:
- United States
- Language:
- English
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