Detection of paternal origin of fetal de novo rea(21q;21q) down syndrome in a pregnancy of a young woman associated with an abnormal first-trimester maternal serum screening result

ObjectiveWe present detection of paternal origin of fetal de novo rea(21q;21q) Down syndrome in a pregnancy of a young woman associated with an abnormal first-trimester maternal serum screening result.Case reportA 26-year-old, gravida 2, para 1, woman underwent amniocentesis at 17 weeks of gestation because of an abnormal first-trimester screening result of 1/139 risk of Down syndrome calculated by 3.109 multiples of the median (MoM) of maternal serum free β-hCG and 0.454 MoM of pregnancy associated plasma protein-A (PAPP-A). Her husband was 29 years old, and the couple had a 1-year-old healthy daughter. Amniocentesis revealed a karyotype of 46,XX,+21,der(21;21)(q10;q10). The pregnancy was terminated at 19 weeks of gestation, and a malformed fetus was delivered. The parental karyotypes were normal. Postnatal analysis of the umbilical cord showed a karyotype of 46,XX,+21,der(21;21) (q10;q10). Polymorphic DNA marker analysis on the DNA extracted from parental bloods and umbilical cord confirmed a paternal origin of the de novo rea(21q;21q) Down syndrome.ConclusionPrenatal diagnosis of de novo rea(21q;21q) Down syndrome should include a polymorphic DNA marker analysis of the parental origin, and the acquired information is useful for genetic counseling of the recurrence of unbalanced rea(21q;21q) offspring and the determination of low-level tissue mosaicism or gonadal mosaicism in one of the parents.