JP,
...the mother was heterozygous for a variant in the gene CYP2D6...

Are you sure she wasn't HOMOzygous??

yep

Genotype analysis was done for cytochrome P450 2D6 (CYP2D6), the enzyme catalysing the O-demethylation of codeine to morphine.2 The mother was heterozygous for a CYP2D6*2A allele with CYP2D6*2×2 gene duplication, classified as an ultra-rapid metaboliser

I missed that part about the gene duplication, though.

So, not only do some people have difficulty metabolizing alcohol (presumably into something less damaging) other people metabolize codeine in to morphine at a much quicker rate (than normal?) and some other people metabolize yet other theraputic drugs at such slow rates that lower doses are required?

Boy, the world sure is a complicated place. Would there be some correlation between these things and racial groups?

Would there be some correlation between these things and racial groups?

yes.
http://jcp.sagepub.com/cgi/conte...ract/44/10/ 1083