48,XXYY, 48,XXXY and 49,XXXXY syndromes: not just variants of Klinefelter syndrome.
Tartaglia N, Ayari N, Howell S, D'Epagnier C, Zeitler P. 48,XXYY, 48,XXXY and 49,XXXXY syndromes: not just variants of Klinefelter syndrome. Acta Paediatr. 2011 Jun; 100(6):851-60.