Metabolism of antipsychotic drugs in asians

I was reading the NICE guidelines on "Consensus statement on high-dose antipsychotic medication", latest (2014) version.

In the section on 'Potential gender and ethnicity factors and high-dose strategies' it says:

Genetic polymorphisms at both the metabolic level and site of action are likely to contribute to the overall response to a particular drug.
Some Asian patients might have a lower dose threshold for a variety of Extrapyramidal side-effects.
Some polymorphisms of the CYP450, 1A2 and 2D6 isoenzymes, which are involved in the metabolism of antipsychotics, give rise to ‘poor metabolizers’ who have higher parent-drug* blood levels for a given dose of these drugs.
There are ethnic differences in the distribution of such poor metabolizers (Reynolds et al, 2006; Bondy & Spellmann, 2007). For example, with CYP2D6, there is a lower incidence of poor metabolizers in the Asian population (1%).
For antipsychotic drugs that are metabolised by CYP2D6 such as risperidone, the risk of high antipsychotic drug levels should be lower in Asians.

Reference: "Consensus statement on high-dose antipsychotic medication", CR190, Royal College of Psychiatrists, Nov 2014.

My Perspective