Pentasomy 49,XXXXY associated with a Chiari type 1 malformation and cervical syrinx.

Pentasomy 49,XXXXY occurs in 1/85,000 newborn males. The origin of this particular form of aneuploidy is believed to be a result of consecutive nondisjunction events during maternal meiosis. Typical presentation consists of hypotonia, developmental delay, various dysmorphic features, and severe hypogenitalism. A 13-year-old with pentasomy 49,XXXXY and a Chiari type 1 malformation with an associated cervical syrinx is presented.