Functional analysis of human CNGA3 mutations associated with colour blindness suggests impaired surface expression of channel mutants A3(R427C) and A3(R563C).
Initial linkage studies with color blindness (CB), glucose-6-phosphate dehydrogenase (G6PD) deficiency, and the blood coagulation factor IX (F9) have suggested that a gene for BP illness is located in the Xq27-q28 region.
Linkage analyses of bipolar disorder with the chromosome 11p15 DNA markers HRAS1 and INS, and the chromosome Xq28 markers for color blindness and G6PD have been reported.
The recent demonstration of genetic linkage between the glucose 6-phosphate dehydrogenase (G6PD)-colour blindness cluster (at Xq28) and the fragile X locus has suggested that the fragile site is indeed the site of the mutation.
These observations and the well-established knowledge that the genes for Deutan and Protan colorblindness are closely linked to G6PD, but segregate independently of factor IX deficiency, suggest that the fragile site associated with this type of X-linked mental retardation occurs in a region prone to high frequency of meiotic recombination.
In three out of the five HA pedigrees of our series that segregate also for G6PD or Deutan color blindness, the observed segregation of the combined phenotypes can be best explained by assuming the occurrence of a fresh mutation in the maternal grandfathers.
Initial linkage studies with color blindness (CB), glucose-6-phosphate dehydrogenase (G6PD) deficiency, and the blood coagulation factor IX (F9) have suggested that a gene for BP illness is located in the Xq27-q28 region.
This study does not replicate previous reports of linkage of MDI to Factor IX (Xq27) and colorblindness region (Xq28) chromosomal markers in other kindreds.