Reciprocal 22q11.2 Deletion and Duplication in Siblings with Karyotypically Normal Parents.

The 22q11.2 locus is known to harbor a high risk for structural variation caused by non-allelic homologous recombination, resulting in deletions and duplications. Here, we describe the first family with one sibling carrying the 22q11 deletion and the other carrying the reciprocal duplication. FISH and SNP array analysis of the parents show a maternal origin for both deletion and duplication, without indications of balanced deletions/duplications or mosaicism. We hypothesize that germline mosaicism in the mother underlies the deletion and duplication, which would implicate a high recurrence risk for her offspring.