Prenatal diagnosis of fragile X in a heterozygous female fetus and postnatal follow-up.

An apparently normal female infant was born after the prenatal diagnosis of fragile Xq27-28 present in about 4 per cent of amniocytes . The mildly retarded mother had been found in early pregnancy to be heterozygous for fragile X. The child, now 9 months old, showed about the same level of fragile X expression as her mother. Variations in the proportion of cells with fragile X appeared to be related to cell type and laboratory techniques. The infant's growth and development have been normal. Different techniques to induce or increase the expression of fragile X are discussed.