Two siblings with partial trisomy 1(q42.3-ter).

Two brothers, aged 6 and 4 years, with an unbalanced chromosome translocation (partial trisomy 1), and their mother, a balanced carrier of the translocation, t(1;3)(q42.3;p26.3), were described. Both patients show minor anomalies; a large head with a prominent forehead, low-set and soaring ears, a high-arched palate, a shallow nasal bridge, hypertelorism, and slender hands and feet. The manifestations in our cases were very mild compared to in the previously reported cases of partial trisomy 1. And our patients exhibit psychomotor retardation and ventricular dilatation on brain CT. We speculated that the amount of extra material reflects the phenotype. Our cases and previous reports indicate that the minimum clinical features of partial trisomy 1 are poor psychomotor development, a prominent forehead, and slender hands and feet. And many cases have macrocephaly with ventricular dilatation or hydrocephalus. So these features may be a key for the diagnosis of very mild partial trisomy 1.