To act, hypocretins must bind to receptors, one of which is rendered non-functional by a mutation carried by patients with narcolepsy. The mutation apparently arose in a common ancestor of these patients, in the HCRTR2 gene located in the vicinity of the HLA-DQB1*0602 and DQA1*0102 alleles. As the mutation occured relatively recently, there has not been enough time for it to be separated from the two HLA-DQ alleles by crossing over in the patients with the most severe cases of narcolepsy. The three genes therefore appear together at frequencies higher than would be expected from random combination of their frequencies in the population, a situation referred as linkage disequilibrium
No comments:
Post a Comment