Late diagnosis of Down syndrome due to incorrect cytogenetic diagnosis and extreme prematurity.

A 26-week gestation, premature neonate who developed a transient myeloproliferative disorder is presented. The morphological features of Down syndrome were not obvious at this gestational age, and the cytogenetic studies gave a misleading normal karyotype after the infant received non-irradiated blood. The diagnosis of Down syndrome was not made until 27 weeks after delivery. The problem of misleading cytogenetic results is discussed in particular in premature infants receiving transfusions with non-irradiated blood products. Although the possibility of uniparental diosomy due to loss of one chromosome 21 was not excluded, this seems to be the first report of a false-normal cytogenetic study after non-irradiated blood.