42 - Bipolar disorder

Bipolar disorder

© SPMM Course  Murray et al. (2002) point out a number of studies that have shown a higher familial risk to be associated with earlier age of onset. Sham et al. (1994) showed that the morbid risk of schizophrenia is greater among the relatives of those probands who had an onset before rather than after age 21 years.  Most case-control studies have not provided evidence in support of COMT associations, but association studies with family design provide greater evidence for COMT in schizophrenia.  In Down’s syndrome, the risk of schizophrenia is same as or lower than the general population. The exact figure is unknown, but an estimate of less than 0.6% is quoted.

C. Genetics of Mood disorders If one parent has a mood disorder, a child will have a risk of between 10 and 25 percent for mood disorder. If both parents are affected, this risk roughly doubles. The presence of more severe mood disorder in the family conveys a greater risk. Bipolar disorder  A family history of bipolar disorder conveys a greater risk for mood disorders in general and bipolar disorder in particular. This may be due to common genetic underpinnings between these two forms of mood disorder. Estimates of broad heritability are high: nearly 85-90%. The lifetime risk in relatives does not vary according to the sex of relative or sex of proband.  Because of its higher prevalence, the unipolar disorder is typically the most common mood disorder in families of bipolar probands.  According to Craddock et al. (2005), lifetime risk of narrowly defined bipolar disorder in relatives of a bipolar proband are: o unrelated member of the general population: 0.5–1.5%; o first degree relative 5–10% (relative risk = 8); o monozygotic co-twin 40–70% (relative risk = 60);  Lifetime risk of unipolar disorder in relatives of a bipolar proband are: o unrelated member of the general population: 5-10%; o first degree relative 10-20% (relative risk = 2-3times); o monozygotic co-twin 15-25% (relative risk = 3-5 times); o Note: You can get the risk of major mood disorder by adding the absolute risk of unipolar and bipolar from the above data.

Genes suspected in Bipolar Disorder

Locus

BDNF (Brain-derived neurotrophic factor) 11p13 DAO G72/G30 D aminoacid oxidase 13q33 COMT Catechol-o-methyl transferase Breakpoint cluster region (BCR) gene 22q11