People with depression that does not respond
to medication could be treated successfully if a simple genetic
blood test was made more widely available in the UK.
Four out of 10 people with depression have a
genetic abnormality that prevents them responding to
anti-depressant medication, according to research presented at the
Royal College of Psychiatrists’ Annual Meeting in London this
week.
The research, which was carried out at the
Mayo Clinic Mood Disorders Unit in the USA, showed that a quarter
of those with a genetic abnormality produce a liver enzyme that
either stops Prozac working or causes unpleasant side-effects.
Since 2003, the Mayo Clinic has offered
genotyping to patients who either report significant side-effects
to antidepressants or have no response.
They have identified four genes that interfere
with the efficacy of antidepressant medication, including two that
prevent metabolising the drug (CYP2D6 and CYP2C19) and two more
that prevent the brain from absorbing or transporting
serotonin.
Professor David Mrazek, chair of the
Department of Psychiatry at the Mayo Clinic College of Medicine,
said: “One in 10 of our patients have abnormal CYP2D6, the gene
most commonly implicated in treatment-resistant depression. This
means that they are poor at metabolising some common
anti-depressant medication including Prozac and Seroxat. As a
result, they may get adverse effects including nausea, headache,
vomiting and sexual problems, from a regular or even low dose of
the drug.”
So far, genotyping – which costs about £150
per gene tested – is not widely available in the UK.
“The cost of the test may be a barrier to more
frequent use of genotyping,” Professor Mrazek said. “But most good
insurance companies now pay for the test for people who have
treatment-resistant depression, either because the drugs don’t work
or they suffer excessive side-effects. It is now proven beyond
doubt that in many cases, unpleasant side effects can be avoided
with this simple blood test.”
Genotyping for depression became widely known
in the USA following publication of the best-seller autobiography,
Mommies Cry Too, by Carolyn Brink in 2006. Brink was
diagnosed with severe postpartum depression shortly after the birth
of her first child. But her treatment with three different
antidepressants made the depression worse and led to suicidal
feelings. She claimed the Mayo Clinic saved her life when the
genotyping test showed that the antidepressant medication she was
taking became toxic in her bloodstream due to her low metabolism
rate for this type of medication.
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References:
The Annual Meeting of the Royal College of Psychiatrists, Imperial College, London, 1 – 4 July 2008