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We report a cytogenetic and molecular cytogenetic study of a novel familial case of 15p tetrasomy due to an extra supernumerary marker chromosome (SMC) (15), which is associated with der (13 ; 14) (q10 ; q10). The proband is a 36-year-old married male with severe oligozoospermia and normal intelligence. He and his pregnant wife attended our department to receive prenatal diagnosis based on the indications of intra-cytoplasmic sperm injection (ICSI) pregnancy and advanced maternal age (39 years). The chromosome analysis of cultured amniocytes showed a Robertsonian translocation between chromosomes 13 and 14 : 45, XX, der (13 ; 14) (q10 ; q10). A cytogenetic examination of the couple revealed that the fetal translocated chromosome is paternally derived, and an extra small bisatellited psudodicentric marker chromosome was detected as a new finding in the husband (proband). Karyotyping of the proband's parents showed that his mother, who is of normal intelligence, carried the same translocation and SMC (15). Although fluorescence in situ hybridization (FISH) with DYZ3, D13/21Z1, D14/22Z1, and SNRPN probes showed no signal on the marker, two strong D15Z1 hybridization signals were found on either side of the centromeric heterochromatin. Thus, the marker chromosome was identified as familial inv dup (15) (pter→q11∷q11→pter) without loci such as the Prader-Willi syndrome (PWS) /Angelman syndrome (AS) critical regions, and we determined that there was a low risk of it affecting the baby's phenotype. Following these results, the pregnancy was continued, and a baby girl was born and developed without any clinically abnormal findings during 3 years after delivery. The coexistence of the two different chrmosome abnormalities in this family might be merely fortuitous.