ABSTRACT
Fragile X syndrome or X-linked mental retardation (XLMP) is one of the most common and perplexing discoveries in modern medical genetics. The association of the fragile X chromosome with mental retardation was originally described by Lubs (1969) in his report of a large kindred with XLNR. The incidence is 1 in 2000 males. It is characterized by moderately severe mental retardation in males and inducible cytogenetic marker (a fragile site) on the long arm of the X chromosome (Xq 27.3). Growth in folate-deficient media or addition of folic acid antagonist methotrexate (MTX), induces expression of fragile X. Phenotypic features include long and narrow face, prominent forehead and jaws, large protruding ears and macroorchidism. Disabilities range from varying degree of learning problems to mental retardation, severe language delay, behaviour problems, autism or autistic-like behaviour, hyperactivity, delayed motor bevelopment and poor sensory skills. Joint hypermobility, hypotonia and mitral valve prolapse are also common features. We reported an eight-year-old male who was referred for evaluation of speech problem and mental retardation. The cytogenetic study demonstrated 46, XY, fra (X) q 27.3. Exhaustive review of literature is also summarized. This is most likely first reported case of fragile X syndrome in Thailand.