Table 1.

Genes involved in dopaminergic pathway.

Receptor	Location	Function and significance	Linkage and association studies	Result
D1 family
DRD1	5q35⋅1	Involved in memory, emotion and cognition, the functions that are highly disturbed in schizophrenics	Grandy et al 1990; Litt et al 1991; Nothen et al 1993a; Cichon et al 1994; Liu et al 1995; Kojima et al 1999	No significant association with any of the polymorphisms
		Several polymorphisms in 5′ and 3′ UTR of the gene (Grandy et al 1990; Litt et al 1991; Dollfus et al 1996; Kojima et al 1999)
DRD5	4p 15⋅3	DRD5 is neuron specific and is localized within the limbic regions of the brain	Asherson et al 1998	No significant association
		Displays high affinity for dopamine
D2 family
DRD2	11q 22-q23	Second most abundant dopamine receptor	Gejman et al 1994; Nanko et al 1994; Asherson et al 1994; Nothen et al 1994; Sobell et al 1994	No significant association
		Higher density of DRD2 in schizophrenic brains (Sedvall and Farde 1995)
		Ser311/Cys311 polymorphism reported (Arinami et al 1994). Cys311 variant more in schizophrenics	Shaikh et al 1994	Positive association
DRD3	3q13⋅3	Expression of DRD3 is restricted to the limbic areas of the brain, site for emotion and cognition that is highly disturbed inschizophrenics	Crocq et al 1992; Nimgaonkar et al 1993; Mant et al 1994	Significant association
		Selective loss of DRD3 mRNA in parietal and motor regions of postmortem schizophrenic brains (Schmauss et al 1993)	Nothen et al 1993b; Jonsson et al 1993; Nanko et al 1993; Chen et al 1997a; Prasad et al 1999	No association
		A to G substitution polymorphism leading to creation of MscI site in exon 1 of DRD3 gene and increased homozygosity at either allele is associated with schizophrenia (Crocq et al 1992)	Please see Jonsson et al (1999) for exhaustive reference
DRD4	11p15⋅5	Higher affinity than other dopamine receptors for atypical antipsychotic clozapine	Sommer et al 1993	No significant association
		Polymorphic 48 base pair repeat in putative third cytoplasmicloop