Cerebellar hypoplasia, zonular cataract, and peripheral neuropathy in trisomy 17 mosaicism

Trisomy 17 mosaicism in liveborns is an extremely rare chromosomal abnormality, with only three cases reported in the literature. Here we describe a 7-year-old boy with trisomy 17 mosaicism. The chromosome abnormality was detected by amniocentesis and was confirmed postnatally in cultured skin fibroblasts. The main clinical features were mental retardation and growth reduction, peripheral motor and sensory neuropathy, hypoplastic cerebellar vermis, zonular cataract, and body asymmetry. In our patient, and in the three earlier described cases, the additional chromosome 17 was detected in skin fibroblasts, not in peripheral lymphocytes. Molecular investigations excluded uniparental disomy of chromosome 17 in our patient. The extra chromosome 17 probably originated from a postzygotic mitotic nondisjunction of the maternal chromosome 17. In most cases of trisomy 17 mosaicism detected in amniocytes the chromosome abnormality seems to be confined to extra-embryonic tissues and clinically normal children are born. If, however, there are also ultrasound abnormalities, the possibility of fetal trisomy 17 mosaicism should certainly be considered. If postnatal karyotyping is limited to blood the diagnosis of trisomy 17 mosaicism could easily be missed. Therefore, we recommend chromosome analysis to be based on cultured skin fibroblasts in all cases where mental retardation is accompanied by postnatal growth retardation, body asymmetry, peripheral neuropathy, and cerebellar hypoplasia or zonular cataract.