Recent research has shown that there are two different allelic DNA sequences distal to the region deleted in FSHD. These alleles are called 4qA and 4qB (Lemmers et al., 2004). Current experience indicates that all patients with FSHD have allele 4qA, while people without FSHD have 4qB.

Testing is available to distinguish between 4qA and 4qB. This additional testing can be requested by calling the Molecular Pathology laboratory 384-9568. A previous FSHD procedure must have been performed before supplemental testing can be performed. Residual DNA should be available and stored in Molecular Pathology, so a new blood sample will, in most cases, not be necessary.