The XXXY variety of Klinefelter syndrome should be suspected when the following features are observed in a mentally retarded boy: decreased upper-lower body segment ratio, microcephaly, clinodactyly with brachymesophalangia of the fifth fingers, and dermatoglyphic arches on nine or ten fingers associated with attriradius in t1 position. These features are not puberty-dependent like the endocrine characteristics of Klinefelter syndrome and, therefore, permit an early diagnosis.
Ferrier PE, Ferrier SA, Pescia G. The XXXY Klinefelter Syndrome in Childhood. Am J Dis Child. 1974;127(1):104-105. doi:10.1001/archpedi.1974.02110200106016