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Down syndrome, the most common birth defect causing mental retardation, is characterized by a specific phenotype including subfertility or sterility and hypogonadism in males. In contrast, several females with Down syndrome have borne offspring. Here, a male with trisomy 21 fathering an infant is described. This observation is verified by serological markers, DNA fingerprinting using different DNA micro‐or minisatellites and andrological investigations.

The Holt‐Oram syndrome was diagnosed in four offspring of three mothers and the same unaffected father. One additional child lacked the characteristic clinical features of the Holt‐Oram syndrome. In contrast to the general autosomal dominant inheritance with complete penetrance, our observation suggests a paternal mutation, resulting in mosaicism, probably restricted to the germline.

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True chromosomal mosaicism of double trisomy (48,XX,+7,+20) was detected in amniotic fluid cell cultures at 16 and 20 weeks of gestation. No aneuploid cells were found in chorionic villus samples (CVS) by semidirect preparation and long‐term culture. High‐level ultrasound did not indicate any structural abnormality of the fetus. At 38 weeks of gestation, a phenotypically normal girl was born. She is now 22 months old and normally developed. At birth, various samples were investigated by routine cytogenetic methods or by fluorescence in situ hybridization with the probe p7t1 (umbilical cord blood, placental tissue, umbilical cord fibroblasts, urine sediment) and no abnormal cells could be detected in any of those tissues. © 1997 John Wiley & Sons, Ltd.

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