***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: A functional polymorphism in the promoter region of the dopamine D2 receptor gene , the -141C Del allele , which may be associated with schizophrenia susceptibility , has previously been described in a Japanese sample . The present study was done in order to examine whether such an association would also be found in a North American schizophrenia patient population . However , analysis of the -141C Del allele frequency in the present group of schizophrenia patients ( n = 50 ) and control subjects ( n = 51 ) did not identify any significant differences . These data support the recent reports on German and British subjects that this genetic variation in the 5'-flanking region of the dopamine D2 receptor gene does not play a major role in the genetic predisposition to schizophrenia Previous studies have demonstrated that subjects with one or two A1 alleles of dopamine D2 receptor ( DRD2 ) polymorphism at the Taq1 A locus have lower DRD2 density than those with no A1 allele . The present study aim ed to examine whether the Taq1 A DRD2 genotypes are related to therapeutic response to nemonapride , a selective dopamine antagonist , in schizophrenic patients . The subjects were 25 acutely exacerbated schizophrenic in patients who had received no medication for at least 1 month before the study . The fixed dose ( 18 mg/day ) of nemonapride was administered to each patient for 3 weeks . The clinical status was prospect ively monitored by the Brief Psychiatric Rating Scale ( BPRS ) before , and 3 weeks after , the treatment . The Taq1 A genotypes ( A1 and A2 alleles ) were determined by the polymerase chain reaction method . Three patients were homozygous for the A1 allele , 11 were heterozygous for the A1 and A2 alleles , and 11 were homozygous for the A2 allele . The patients with one or two A1 alleles ( n = 14 ) showed significantly higher percentage improvement in total BPRS and positive symptoms than those with no A1 allele ( n = 11 ) after 3-week treatment while the percentage improvement in other subgrouped symptoms ( negative , anxiety-depression , excitement and cognitive symptoms ) was similar between the two genotype groups . The present results suggest that the Taq1 A DRD2 polymorphism is related to early therapeutic response to nemonapride in schizophrenic patients , possibly by modifying the efficiency of DRD2 antagonism of the drug in the central nervous system The relationship between Taq1 A polymorphism of dopamine D(2 ) receptor ( DRD(2 ) ) gene and extrapyramidal adverse effects of bromperidol and nemonapride , which are both antipsychotic drugs with selective and potent DRD(2 ) antagonistic property , was investigated in Japanese schizophrenic in patients . Twenty-seven patients were treated with bromperidol  at 6 or 12 or 18 mg/day , while 25 patients were treated with nemonapride  at 18 mg/day . The duration of treatment was 3 weeks . The A1 and A2 alleles were determined by PCR . The extrapyramidal adverse effects were assessed by the Udvalg for Kliniske Unders¿ogelser side effects rating scale . Six patients were homozygous for the A1 allele , 27 were heterozygous for the A1 and A2 alleles , and 19 were homozygous for the A2 allele . There were no significant differences in the incidences or severity of extrapyramidal adverse effects between the patients with one or two A1 alleles and those with no A1 allele . The present study suggests that Taq1 A polymorphism is not related to the development of extrapyramidal adverse effects during acute phase of bromperidol and nemonapride treatments Neuroleptic drugs have a high affinity for the dopamine D2 receptor ( DRD2 ) ; therefore DRD2 is thought to be a c and i date gene for schizophrenia . Arinami et al. have reported a positive association between schizophrenia and the Cys311 variant of the DRD2 gene . We determined the allele frequency of this polymorphism in 78 Okinawan schizophrenic patients and 112 control subjects . The patients and controls did not differ significantly in allele frequencies of Cys311 The result of most association studies and linkage analyses have suggested a negative association between schizophrenia and D2-like ( D2 , D3 , and D4 ) receptor polymorphisms . Although the polymorphisms of the D2-like receptor in themselves may not account for the etiology of schizophrenia , they can contribute to the severity of the symptoms . Thus , we studied the associations between the polymorphisms and their combinations , and the vulnerability of schizophrenics . Fragments of the D2-like receptor genes were amplified by means of the polymerase chain reaction , and the polymorphisms were identified by the restriction fragment length polymorphism and single-str and ed conformation polymorphism methods . There were no statistically significant differences in the polymorphisms and their combinations between schizophrenics and controls . Schizophrenics with D4E1(A1/A2 ) , which contains 2 and 1 t and em repeats of a 12-base-pair sequence in exon 1 , had a lower total positive symptom score before medication than schizophrenics with D4E1(A1/A1 ) . There was no association between the polymorphisms and negative symptoms 
    Output:
    
Conclusion Our meta- analysis suggests an association of the DRD2 gene and the risk for schizophrenia , given that TaqI and C957 T polymorphisms presented a protective effect against schizophrenia , and in the sub-analyses the C957 T variant increased the risk for this disorder in the Chinese population