Case 19-2003: a five-day-old girl with leukocytosis and a worsening rash from birth

A five-day-old girl with a rash and an elevated white blood cell count was diagnosed with transient myeloproliferative disorder associated with trisomy 21. Trisomy 21 usually causes Down syndrome, but in this girl, only the white blood cells had trisomy 21. Thirty-five days after her birth, the abnormal white blood cells had disappeared and she no longer had trisomy 21.