fragile X syndrome
Definition: an X-linked recessive syndrome consisting of mental retardation, a characteristic facies, and macroorchidism. DNA analysis shows abnormal trinucleotide repeats on the X chromosome near the end of its long arm, at Xq27.3. Constriction is demonstrable at this site on karyotyping after culture in folate-deficient medium.
See Also: Renpenning syndrome