OBJECTIVE:

To inform clinicians about fertility in males with Down syndrome.

DESIGN:

Case report.

SETTING:

Medical Genetics Department of a tertiary-care hospital.

PATIENT(S):

A 26-year-old man with confirmed nonmosaic trisomy 21.

INTERVENTION(S):

Karyotype, amniocentesis, paternity testing using microsatellite markers.

MAIN OUTCOME MEASURE(S):

Confirmed paternity in the son of a male with nonmosaic trisomy 21.

RESULT(S):

A male with nonmosaic Down syndrome fathered a normal son, and the paternity was proven by microsatellite marker analysis.

CONCLUSION(S):

Although Down syndrome males have been reported to be infertile, it may not always be true. Infertility in males has been attributed to defective spermatogenesis, but ignorance of the sexual act may be one of the contributing factors. It is important to advise postpubertal Down syndrome males on contraceptive measures.