Dopamine receptor
Monozygotic (identical) but not dizygotic (fraternal) twins tend to have similar sleep habits. Neurotransmitters, molecules whose production can be traced to specific genes, are one genetic influence on sleep that can be analyzed. The circadian clock has its own set of genes. Genes which may influence sleep include ABCC9, DEC2, Dopamine receptor D2 and variants near PAX 8 and VRK2.