Mosaic partial trisomy 17 q 2

Examination of an infant born after prenatal diagnosis of mosaic partial trisomy 17q2 showed the unique phenotypic features of this chromosomal abnormality, that is, frontal bossing, large mouth, brachyrhizomelia, and hexadactyly. Amniocentesis was performed because of polyhydramnios and ultrasound diagnosis of fetal craniofacial dysmorphology and rhizomelic shortening of the limbs. Chromosomal mosaicism was restricted to fetal tissue and amniotic fluid cells. The placental chromosomal complement was normal, suggesting that the abnormality developed after differentiation of embryonic and trophoblastic cells. This emphasises the usefulness of cytogenetic evaluation of placental, fetal, and amniotic fluid cells in delineating the pathogenesis of congenital abnormalities. Partial trisomy 17q2 is rare. The reported cases have involved a variable length of 17q from band q21,"2 q22,3 q23," and q25. 1.9 Despite the difference in the size of the chromosome segment involved, there is strong phenotypic resemblance in the reported cases. The diagnosis has previously been made in infancy or early adulthood. One case9 was diagnosed by amniocentesis in the second trimester of pregnancy after diagnosis of the disorder in an affected sib and the discovery of a maternal balanced translocation. All previously reported cases, apart from the one described by Fryns et al,3 have been the result of a familial translocation. Case report The parents were non-consanguineous. Neither parent had any phenotypic abnormalities and they had one normal 3 year old daughter. The mother was 28 Department of Obstetrics and Gynaecology, University of Hong Kong, Hong Kong. P A King, A Ghosh, M Tang Correspondence to Dr King, Department of Obstetrics and Gynaecology, Queen Mary Hospital, Pokfulam Road, Pokfulam, Hong Kong. and the father was 46 years old when the infant was