PMM2 and familial hemiplegic migraine: In the search for the biological link between PMM2-CDG and FHM, there is some evidence, using experimental generation of impaired N-glycosylation at CACNA1A channel and evaluating the subsequent gating abnormalities, that impaired N-glycosylation leads to a gain-of-function on CACNA1A channel, similar to mutations causing FHM (8).