Major depressive disorder (MDD) is a common and serious clinical disease that reduces patients' productivity and lowers the quality of their lives. The pathogenesis for the cause of depression is associated with the reduction in the serotonergic neurotransmitter system.1–3 It has been proven that the serotonergic neurotransmitter system engages in the regulation of affective disorder and a wide range of psychological and behavioral functions.4–7 The serotonin 1A receptor (5-HTR1A) gene has become the candidate gene in the genetic pharmacology of SSRIs (selective serotonin reuptake inhibitors), which is the major medicine for depression in clinical therapies.8 The 5-HTR1A gene, mapped to chromosome 5q11.2-q13, is intron-less and codes for a 422-amino-acid protein.9 Some previous studies showed that a 5-HTR1A C(-1019)G polymorphism had a certain correlation with depression and other mental diseases, as well as its patients' correlative personality. But there were other studies that failed to discover that a 5-HTR1A C(-1019)G polymorphism had any relation with depression or suicidal behavior.
Controversial results of related studies might be due to factors such as limited sample size and ethnic heterogeneity. There have been no studies on the association between 5-HTR1A C(-1019)G polymorphism and MDD in the Northern Han ethnic Chinese population so far. Therefore, we designed this study to assess the association between C(-1019)G of 5-HTR1A and MDD in the Northern Han ethnic group of China and discussed their association in sex, age at onset and family history so as to further clarify relevant hereditary mechanism of MDD.
A total of 400 MDD patients (185 male, 215 female), at a mean age of (34±13) years, were from the Department of Psychiatry, First Hospital of Shanxi Medical University, China from May 2004 to March 2007. All patients were chosen for the group under the same instructions with the Diagnostic Investigation Genet Scale (DIGS) developed by Harvard University in the United States and by two strictly-trained psychiatrists with rich clinical experience according to American drawback diagnose and the statistical handbook beta 4th edition (DSM-IV). The history of the patients in the group was recorded in detail including their histories of disease, hospitalization, and medication in clinical therapy, excluding any hereditary diseases, severe physical diseases and other mental disorder.
A total of 400 normal control subjects (185 male, 215 female), with a mean age of (29±11) years, were randomly recruited from healthy volunteers at the same time. All control subjects were healthy blood donors from the same district without apparent mental or physical diseases, positive family history of mental disease and without blood relationship. All subjects were willing to participate in this research and signed the informed consents.
All the patients and control subjects were of Northern Han Chinese population descent. The criterion of the Northern Han Chinese descent was met when “two parents and four grandparents originated from Northern Han Chinese population” and they were matched in age and sex.
DNA was isolated from whole blood by standard techniques. 5-HTR1A C(-1019)G variants were determined with polymerase chain reaction (PCR) techniques. We designed a sense primer (5′-TGTCGTCGTTGTTCGTTTGT-3′) and an antisense primer (5′-CGTGTCAGCATCCCAGAGTG-3′). All primers were designed by Primer 5.0 software and its specificity was validated by using BLASTN in the human genome database of the National Center for Biotechnology Information (http://www.Ncbi.nlm.nih.gov/BLAST/). The PCR was carried out in a 25 μl reaction volume containing 2.5 μl 10×GC buffer (Tiangen, Beijing, China), 200 μmol/L of dNTP, 0.2 μmol/L of each primer, 1.0 unit of Tag DNA polymerase (Tiangen), and 60 ng of genomic DNA. After heat denaturation of the samples (10 minutes at 95°C), 35 cycles were carried out consisting of 30 seconds at 95°C, annealing at 60°C for 30 seconds and extension at 72°C for 30 seconds, followed by a final extension at 72°C for 10 minutes. The products of PCR remained at 4°C and were purified by using a Multi Screen-PCR plate (Millipore). The purified PCR products were bidirectional sequenced by using the ABI 3700 DNA sequencer (Pekin-Elmer, Applied Biosystems, Foster City, CA, USA).
The Hardy-Weinberg equilibrium was tested with the Chi-square (χ2) goodness-of-fit test. The frequencies of genotype and allele were also compared between the patients and control subjects by using the Pearson Chi-square analysis. The significance level was set at a P value of less than 0.05.
Genotype distribution was in agreement with the Hardy-Weinberg equilibrium both in control subjects and patients (P>0.05, data not shown).
Results of the genotype distribution and allele frequency for this polymorphism in patients and control subjects are summarized in Tables 1 and 2. There was a significant difference in the genotype distribution and allele frequency between patients and control subjects. Moreover, a significant difference in the genotype distribution and the allele frequency was found between the patients and the controls in the female and late-onset subjects (>30 years).
Our results showed a statistically significant association of 5-HTR1A C(-1019)G polymorphism with MDD. A previous study in a limited Spanish sample of patients with MDD showed no association between the C(-1019)G polymorphism at the 5-HTR1A gene and the disorder.10 In contrast, a study by Lemonde comparing 129 MDD patients and 134 control subjects from Canada showed a strong association between this polymorphism and the disease.11 Moreover, in Lemonde's sample, the C/C genotype was significantly less associated with MDD.11 Conversely, the G/G genotype was less in our samples. It is possible that this linkage disequilibrium may not occur in all kinds of populations. So large replication studies with different ethic samples are needed to investigate whether there are ethnic differences in the influence of the C(-1019)G polymorphism of 5-HTR1A on MDD. This issue should be investigated with different ethnic samples in the future.
The strength of our study is susceptible to population stratification. Several studies have reported that 5-HTR1A C(-1019)G polymorphism could be the susceptible factor in female depressive patients and the result is the same with our study's. However, a previous study12 showed that early-onset MDD (≤30 years old) has a more malignant course and is more associated with increased comorbidity than with late-onset major MDD (>30 years old), which is contrary to the result of our study. A polymorphism of a single gene might produce a false-positive or false-negative result by chance rather than reveal a direct causal relation when we interpret the association between polymorphism of a gene and a disease. But all subjects matched for age and sex were unrelated Northern Han Chinese. Furthermore, the healthy control subjects were interviewed according to the same standard. Thus a false-positive or false-negative result in our study is unlikely.
As to limitations, our study may control other factors, because the incidence of MDD is the interaction of genetic and environmental factors. Therefore, the result will be more objective if the study of genotype distribution and allele frequency is made after controlling the environment.
In conclusion, we found an association between a 5-HTR1A C(-1019)G polymorphism and MDD in the Northern Han ethnic group of China. In addition, this polymorphism may be a susceptible factor in both female and late-onset MDD patients in them. Further studies need to be carried out in different ethnic groups to investigate whether there are ethnic differences in the influence of the 5-HTR1A C(-1019)G polymorphism on MDD.
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