Identification of a small supernumerary marker chromosome, r(2)(p10q11.2),and the problem of determining prognosis

The identification of small supernumerary marker chromosomes (SMCs) and the elucidation of their clinical significance remain two of the problems in c lassical human cytogenetics. We observed a small supernumerary ring in amni otic fluid cell cultures and identified its origin as r(2)(p10q11.2) and it s extent by means of fluorescent in situ hybridisation (FISH). Uniparental disomy (UPD) was excluded by microsatellite analysis using polymorphic mark ers localised in the same region. On the basis of normal ultrasonographic c hecks, the patient decided to continue the pregnancy. A normal female was d elivered at term and subsequent neonatal follow-ups confirmed the normal ph enotype and development. In the present case, genetic counselling was not h elpful because of the absence of reference cases. Detailed characterisation made it possible td correlate the normal baby phenotype with the trisomic 2p10-2q11.2 genomic region. Further molecular cytogenetic investigations of SMCs classified by DNA content and pregnancy outcome data should improve g enetic counselling and risk evaluation. Copyright (C) 2001 John Wiley & Son s, Ltd.