Recombinant Down syndrome: a case report and literature review

We report a case of a child with features of Down syndrome (DS) but with an atypical karyotype. Initial chromosome analysis was 46,XX,dup(21q).ish 21(wcp21+). The father's chromosomes were normal. However, the mother was found to have mosaicism for a pericentric inversion of chromosome 21 (19/30 cells). The revised chromosome result of the child was 46,XX,rec(21)dup(21q)inv(21)(p12q21.1)mat. A literature review of similar cases (hereafter referred to as rec dup(21q)) was conducted to aid counselling about recurrence risks and the prognosis for this child. All previous reports of rec dup(21q) were secondary to a maternal pericentric inversion. Male carriers did not seem to be at risk of having offspring with the rec dup(21q), although the number of male carriers was limited. In those with rec dup(21q), the risk of congenital heart disease was similar to that of trisomy 21. In reported cases, the facial appearance was suggestive of Down syndrome but perhaps less striking. Although the data are limited, there is an indication the developmental disabilities and short stature are milder in those with rec dup(21q) compared to trisomy 21. These observations promote the concept that the region of chromosome 21 proximal to the duplication contains genetic information contributing to the expression of some features of Down syndrome.