Molecular analysis of mutations in the gene FMR-1 segregating in fragile X families.

Molecular genetic analysis of the transmission of mutations in 73 families with fragile X (one of the largest samples evaluated so far) has confirmed previous hypotheses that the fragile X syndrome results from two consecutive mutational steps, designated "premutation" and "full fragile X mutation". These mutations give rise to expansions of restriction fragments, most probably by amplification of the FMR-1 CGG repeat. Premutations are identified by small expansions that apparently have no effect on either the clinical or the cellular phenotype.

Progressive myopathy in trisomy 21.

A 23-year-old female patient with clinical manifestations typical of Down's syndrome progressively developed intensifying weakness of the proximal muscles from the age of 16 years. CK levels were distinctly elevated. Electromyography showed myogenic lesions and muscle biopsy a myopathic image with extensive fibre hypertrophy.