diagnostic tests

Last reviewed 01/2018

The presence of the trinucleotide repeats in FMR-1 is the basis of two diagnostic tests:

• cytogenetic - culture of patients' cells in medium which inhibits folate metabolism results in breakage of the X chromosome at Xq27.3, within the CGG repeats

• DNA - Southern blots will show the presence of an expanded series of CGG repeats

Note that it is generally felt that a diagnosis made or refuted before 1990 should not be trusted.

The question of when to test assymptomatic female siblings for their carrier status is difficult, and most areas have a local policy.