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Editor—Partial trisomy mosaicism describes the presence of a normal cell line together with an unbalanced translocation in a second cell line. Its incidence is not known. Only a few cases have been published,1 almost all with developmental delay and a pattern of dysmorphism. The presence of a normal cell line points towards postzygotic formation, but the origin and mechanism of formation have so far only been investigated in one case of partial trisomy 16p mosaicism and in another case of partial trisomy 21q mosaicism.2 3 In the former, a complex formation by trisomy first, translocation second, and uniparental disomy and partial trisomy third was inferred. In the latter, paternal meiotic origin of der(21;21)(q10;q10) mosaicism (46,XX/46,XX,der(21;21)(q10;q10),+21) in a girl with mild Down syndrome was described.
Here, we report on a 25 year old woman with mental retardation, dysmorphic features, partial trisomy 11q13→qter mosaicism (46,XX, der(19)t(11;19)(q13;p13.3)/46,XX), maternal uniparental isodisomy 11q13→qter in the normal cell line, and two maternal and one paternal segment(s) 11q13→qter in the abnrmal cell line.
Case report
The female patient is the second child of a healthy, unrelated, white couple. An older brother is healthy. At the proband's birth, her mother was 38 years old and her father was 39 years old. Following information, the parents opted against prenatal cytogenetic diagnosis. Delivery by caesarean section took place at 42 weeks of a normal gestation. Weight (2500 g) and length (48 cm) were below the 10th centile. A right inguinal hernia, ipsilateral pes equinovarus, and left hip dysplasia were surgically corrected. At the age of 6 years, height (1.7 m) was on the 10th centile, weight (22 kg) on the 75th centile, and occipitofrontal head circumference (OFC) (51 cm) on the 50th centile. At the last re-examination at the age of 25 years, height (1.50 m) was below …