The limitations of the current study include the low number of SNPs investigated and the fact that the genetic variation across the whole GHRL and GHSR genes are not taken into account. The best genetic models were recessive for AUDIT scores and dominant for smoking. A possible explanation to this discrepancy may be a threshold effect of the SNP on the various parameters i.e. while heterozygosity is enough to infer an increased risk in smoking, one needs to be homozygote for the risk allele in order to have an increased probability of having higher AUDIT scores. As nicotine is more addictive than alcohol (van Amsterdam et al. 2010), it is not farfetched to suggest that fewer genetic risk factors are needed to become addicted to nicotine. The poor fit with a recessive model for smoking explains why effect sizes for AUDIT are unchanged when controlling for smoking and a similar argument holds when controlling for AUDIT.
