Duplication of 7p21.2 -> pter due to maternal 7p;21q translocation: implications for critical segment assignment in the 7p duplication syndrome

We describe a 1-year-old boy with mental and physical retardation, a large anterior fontanel, brachycephaly with flat occiput, short and stubby finger s, generalized hypotonia, ocular hypertelorism, low-nasal bridge, long phil trum, high-narrow palate, apparently low-set ears, and a small mandible. Cy togenetic analysis utilizing high resolution chromosome banding technique s howed an unbalanced karyotype consisting of 46,XY,add(21)(q22.3) that origi nated from maternal balanced translocation between chromosomes 7 and 21. Fl uorescence in situ hybridization (FISH) using microdissected library probe pool from chromosome 7 confirmed the additional material on 21q was derived from chromosome 7. Our results indicated that the patient had an unbalance d translocation, 46,XY,der(21)t(7;21)(p21.2;q22.3)mat, which resulted in du plication for distal 7p. Our patient is similar to reported cases with a 7p 15-->pter or larger duplication of 7p, suggesting that the critical segment causing the characteristic phenotype of 7p duplication syndrome, including large anterior fontanel, exists at 7p21.2 or 7p21.2-->pter. Am. J. Med. Ge net. 86:305-311, 1999. (C) 1999 Wiley-Liss, Inc.