45,X/46,XY mosaicism remains undetected in some short boys because this group is not routinely karyotyped. We recommend chromosomal analysis of boys with otherwise unexplained short stature who are short for their families. Growth hormone treatment should be offered to short boys with 45,X/46,XY mosaicism and a predicted adult height below the mid-parental range within clinical trials.

Presence of the GBY locus in Turner patients with no indication of the Y chromosome in standard cytogenetic chromosome analysis can be revealed by sensitive molecular PCR assays screening for presence of the Y centromere and the GBY-candidate-genes in proximal Yp11 and Yq11, respectively.

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We describe a girl with short stature, mild mental retardation, hemihypotrophy, atrial septal defect I, bilateral branchial cleft fistulas and abnormal skin pigmentation. Growth hormone deficiency and other frequent causes of short stature were excluded. Blood karyotype was investigated twice. In one sample an additional marker chromosome was found in one of 53 analysed metaphases, which could not be further characterized, whereas a second investigation showed a normal female karyotype. Cytogenetic studies in skin fibroblasts revealed a mosaic trisomy 15. Although mosaic trisomy 15 is a rare finding the diagnosis must be considered in the presence of pigmentary changes, body asymmetry, short stature and other minor dysmorphic signs even if blood karyotype is normal.