Causes of individual differences in happiness, as assessed with the Subjective 
Happiness Scale, are investigated in a large of sample twins and siblings from 
the Netherlands Twin Register. Over 12,000 twins and siblings, average age 24.7 
years (range 12 to 88), took part in the study. A genetic model with an age by 
sex design was fitted to the data with structural equation modeling in Mx. The 
heritability of happiness was estimated at 22% for males and 41% in females. No 
effect of age was observed. To identify the genomic regions contributing to this 
heritability, a genome-wide linkage study for happiness was conducted in sibling 
pairs. A subsample of 1157 offspring from 441 families was genotyped with an 
average of 371 micro-satellite markers per individual. Phenotype and genotype 
data were analyzed in MERLIN with multipoint variance component linkage analysis 
and age and sex as covariates. A linkage signal (logarithm of odds score 2.73, 
empirical p value 0.095) was obtained at the end of the long arm of chromosome 
19 for marker D19S254 at 110 cM. A second suggestive linkage peak was found at 
the short arm of chromosome 1 (LOD of 2.37) at 153 cM, marker D1S534 (empirical 
p value of .209). These two regions of interest are not overlapping with the 
regions found for contrasting phenotypes (such as depression, which is 
negatively associated with happiness). Further linkage and future association 
studies are warranted.