Trisomy of distal portion of long arm of chromosome 2, an abnormality found in two unrelated families associated with mental retardation

Study of 2 cases of mental retardation from separate unrelated families led to the detection of an apparently previously undescribed chromosome abnormality, trisomy of the distal portion of chromosome 2 secondary to familial translocation. Case I, a 6 year old boy, presented with mental retardation, cleft palate and abnormal facies. The patient's brother died with a similar clinical picture in childhood. Chromosome analysis on the patient demonstrated partial trisomy of the distal portion of the long arm of chromosome 2: 46,XY, -9,+t(2,9)(2qter → 2q33: :9pter → 9qter). Trisomy is believed to come from maternal sources: 3 maternal uncles show cleft palate and abnormal ocular findings including hypertelorism, optic atrophy, recurrent conjunctivitis and corneal pathology and the same chromosome abnormality. The patient's sister, mother and maternal grandmother exhibit balanced translocation on chromosome analysis: 46,XX,2q-, -9, t(2qter → 2q33: :9p24 9qter). Case II, a 3 month old female, presented with mental retardation, hypertelorism, flat occiput, frontal bossing and urinary tract anomalies. Chromosome analysis demonstrated the following pattern: 46,XX, -9, +t(2;9) (2qter → 2q31: 9pter → 9qter). Chromosome analysis demonstrated a normal karyotype in the mother; the father and paternal uncle show a balanced translocation: 46,XY, 2q-, -9, t(2;9) (2qter →2q31: :9pter → 9qter). Clinical differences between patients of the 2 families may result from variations in translocated chromosomal material.