Sequencing of canine 5-hydroxytriptamine receptor (5-HTR) 1B, 2A, 2C genes and identification of polymorphisms in the 5-HTR1B gene

5-HTR2A and IL-6 polymorphisms and obstructive sleep apnea-hypopnea syndrome

At present, variants of the 5-hydroxytryptamine receptor 2A (5-HTR2A) and interleukin-6 (IL-6) genes may be susceptible markers to develop for obstructive sleep apnea-hypopnea syndrome (OSAHS). Therefore, the aim of the present study was to explore the potential associations between the 5-HTR2A and IL-6 single-nucleotide polymorphisms (SNPs) and OSAHS. In total there were 130 cases and 136 controls collected for genotyping of 5-HTR2A (rs6311) and IL-6 (rs1800796) SNPs. The association of these SNPs with OSAHS risk were evaluated by computing the odds ratio (OR) and 95% confidence interval (CI) from multivariate unconditional logistic regression analyses with adjustment for gender and age. The results indicated that the genotype and allele frequencies in these two loci (rs6311 and rs1800796) were not significantly different between the cases and controls. However, carrying the 'C' allele of rs6311 has a protective effect against OSAHS via the gender-specific comparison (P=0.0409; OR, 1.744; 95% CI, 1.021-2.978). The 'G' allele and 'CG' genotype distribution of rs1800796, and 'C' allele and 'CT' genotype distribution of rs6311 have significant differences between the mild and moderate group (P<0.05). Similarly, the genotype distribution of rs6311 has differences between mild and severe cases (P=0.0026). The current research demonstrated that variants of rs6311 have an association with OSAHS in males. Additionally, polymorphisms of rs6311 and rs1800796 have relevance to the severity of OSAHS.

Obstructive sleep apnea syndrome susceptible genes in the Chinese population: a meta-analysis of 21 case-control studies

BACKGROUND

Numbers of single nucleotide polymorphisms (SNPs) were identified as risk factors for obstructive sleep apnea syndrome (OSAS) in the Chinese population; however, published articles drew incompatible or even contradictory results.

OBJECTIVE

The aim of this study was to investigate the susceptible SNPs and risk of OSAS in the Chinese population.

METHODS

We conducted a meta-analysis of seven polymorphisms and risk of OSAS based on 21 case-control studies.

RESULTS

The results of our study showed that tumor necrosis factor-α (TNF-α) -308 G/A (OR = 3.70, 95 % CI = 1.39-9.83), gene-linked polymorphic region (LPR) (OR = 0.57, 95 % CI = 0.41-0.79), and variable number tandem repeat (VNTR) of the 5-hydroxytryptamine transporter gene (5-HTT) (OR = 3.44, 95 % CI = 1.49-7.95) polymorphisms were associated with OSAS risk in the Chinese population, while there was no significant association between 5-hydroxytryptamine 2A receptor (5-HTR2A) 102C/T, 5-HTR2A A1438G, angiotensin-converting enzyme (ACE) insertion (I)/deletion (D), or leptin receptor (LEPR)-Gln 223Arg polymorphism and risk of OSAS in the Chinese population.

CONCLUSIONS

Our study demonstrated that TNF-α 308 G/A, 5-HTT LPR, and 5-HTT-VNTR polymorphisms were associated with OSAS risk, whereas little association was observed between 5-HTR2A 102C/T, 5-HTR2A A1438G, ACE I/D, or LEPR-Gln 223Arg polymorphism and risk of OSAS in the Chinese population.

A systematic review and meta-analysis of the association between serotonergic gene polymorphisms and obstructive sleep apnea syndrome

Background

5-Hydroxytryptamine receptor (5-HTR) and 5-hydroxytryptamine transporter (5-HTT) gene polymorphisms have been reported to be associated with susceptibility to obstructive sleep apnea syndrome (OSAS). The associations, derived from sporadic, inconsistent, small-sample-size studies, need to be evaluated further in a meta-analysis.

Methods

Relevant studies were identified by searching PubMed, Embase, The Cochrane Library, China National Knowledge Infrastructure (CNKI), Wanfang, and Weipu. Eligible data were extracted from each included study. Odds ratios (ORs) were calculated using a fixed-effects or a random-effects model. The ORs and 95% confidence interval (CI) were used to assess the strength of the association between serotonergic gene polymorphisms and OSAS in the dominant and recessive models, as well as alleles. The Q statistic was used to evaluate homogeneity and Begg’s test was used to assess publication bias.

Results

Eight studies were finally included in the meta-analysis of the association between 5-HTR2A gene variants (including 102T/C and 1438G/A), 5-HTT gene polymorphisms (including 5-HTT gene-linked promoter region (5-HTTLRP), and serotonin transporter intron 2 variable number tandem repeat (STin2VNTR) and OSAS risk. The G allele of 5-HTR2A 1438G/A, long 5-HTTLPR, and 10-tandem-repeats STin2VNTR were shown to increase OSAS susceptibility, with ORs of 2.33 (A vs. G, 95% CI 1.48–3.66), 1.24 (L vs. S, 95% CI: 1.04–1.49), and 2.87 (10 vs. 12, 95% CI: 1.38–5.97), respectively. These significant differences were determined in both dominant and recessive models. Of the 5-HTR2A 1438G/A gene polymorphism, the AA genotype increased the OSAS risk, with an OR of 4.21 (95% CI: 2.83–6.25) in a recessive model in male OSAS patients, but no significant association was found in females.

Conclusions

Our meta-analysis demonstrated that polymorphisms in the 5-HTR2A 1438G/A and 5-HTT genes contributed to susceptibility to OSAS. The A allele of the 1438G/A gene polymorphism is predominantly distributed in males and increased the OSAS risk significantly.

Polymorphisms of the 5-hydroxytryptamine 2A/2C receptor genes and 5-hydroxytryptamine transporter gene in Chinese patients with OSAHS

BACKGROUND

It is known that there is a genetic predisposition to OSAHS. Polymorphisms of the 5-hydroxytryptamine (5-HT) 2A/2C receptors (5-HTR 2A/2C) genes and 5-HT transporter (5-HTT) gene may be associated with the pathogenesis of obstructive sleep apnea-hypopnea syndrome (OSAHS).

OBJECTIVES

In this study, we aimed to investigate the prevalence of polymorphisms of the 5-HTR 2A/2C genes and the 5-HTT gene in the Chinese Han OSAHS population.

METHODS

A total of 226 unrelated subjects of the Chinese Han population, including 121 OSAHS patients and 105 healthy controls, were involved in the study. The A1438G and T102C polymorphisms of the 5-HTR 2A gene, G796C polymorphisms of the 5-HTR 2C gene, and two polymorphisms (gene-linked polymorphic region [LPR] and variable number tandem repeat [VNTR]) of the 5-HTT gene were identified by polymerase chain reaction (PCR)-RFLP.

RESULTS

Compared with the control group, the OSAHS group had significantly higher AA genotype and A allele frequencies in the A1438G polymorphisms of the 5-HTR 2A gene, and had significantly higher frequencies of 10/10, 12/10 genotypes and the allele 10 of 5-HTT-VNTR. There were no significant differences between the genotype distribution and allele frequencies of the OSAHS group and the control group regarding the T102C polymorphisms of the 5-HTR 2A gene and the G796C polymorphisms of the 5-HTR 2C gene, the frequencies of the S or L allele and the S/S, S/L or L/L genotypes in 5-HTT-LPR.

CONCLUSIONS

The A1438G polymorphism of the 5-HTR 2A gene might be involved in the pathogenesis in OSAHS subjects of the Chinese Han population. Meanwhile, our findings support the argument that 5-HTT polymorphism appears to be associated with susceptibility to OSAHS, because the allele 10 of 5-HTT-VNTR might be a susceptible factor.

Sequences and polymorphisms of the canine monoamine transporter genes SLC6A2, SLC6A3, and SLC6A4 among five dog breeds

Monoamine transporters have roles to regulate the monoamine concentrations in synaptic clefts in the central nervous system and are the targets of antidepressants and psychostimulants. They include transporters for norepinephrine, dopamine and serotonin, which are encoded by the SLC6A2, SLC6A3, and SLC6A4 genes, respectivily. We sequenced the full lengths of the coding regions of these genes for dogs and identified four single nucleotide polymorphisms (SNPs) in SLC6A2 and four in SLC6A3. One SLC6A3 SNP was non-synonymous and caused an amino acid substitution from threonine to serine. The genotype frequencies of these polymorphisms differed significantly among five breeds with different behavioral traits, suggesting that novel SLC6A2 and SLC6A3 SNPs would provide additional useful information for behavioral genetic studies in dogs.

Identifying novel polymorphisms in the canine tryptophan hydroxylase 2 gene

Tryptophan hydroxylase (TPH) serves as the rate-limiting enzyme in the biosynthesis of serotonin, and two forms of TPH genes, TPH1 and TPH2, have been reported with specific nucleotide sequences and expression patterns. We determined the sequences of these two genes and identified polymorphisms within their coding regions. We identified five novel single nucleotide polymorphisms in the TPH2 gene, one of which resulted in a non-synonymous mutation and the remaining four in synonymous mutations. Comparison of the genotype frequencies of the polymorphisms among five popular breeds with different behavioral traits revealed statistically significant interbreed differences for three polymorphisms. These results suggest that these polymorphisms would be useful genetic markers when performing behavior studies in dogs.

Single nucleotide polymorphisms (SNPs) in coding regions of canine dopamine- and serotonin-related genes

Background

Polymorphism in genes of regulating enzymes, transporters and receptors of the neurotransmitters of the central nervous system have been associated with altered behaviour, and single nucleotide polymorphisms (SNPs) represent the most frequent type of genetic variation. The serotonin and dopamine signalling systems have a central influence on different behavioural phenotypes, both of invertebrates and vertebrates, and this study was undertaken in order to explore genetic variation that may be associated with variation in behaviour.

Results

Single nucleotide polymorphisms in canine genes related to behaviour were identified by individually sequencing eight dogs (Canis familiaris) of different breeds. Eighteen genes from the dopamine and the serotonin systems were screened, revealing 34 SNPs distributed in 14 of the 18 selected genes. A total of 24,895 bp coding sequence was sequenced yielding an average frequency of one SNP per 732 bp (1/732). A total of 11 non-synonymous SNPs (nsSNPs), which may be involved in alteration of protein function, were detected. Of these 11 nsSNPs, six resulted in a substitution of amino acid residue with concomitant change in structural parameters.

Conclusion

We have identified a number of coding SNPs in behaviour-related genes, several of which change the amino acids of the proteins. Some of the canine SNPs exist in codons that are evolutionary conserved between five compared species, and predictions indicate that they may have a functional effect on the protein. The reported coding SNP frequency of the studied genes falls within the range of SNP frequencies reported earlier in the dog and other mammalian species. Novel SNPs are presented and the results show a significant genetic variation in expressed sequences in this group of genes. The results can contribute to an improved understanding of the genetics of behaviour.

Polymorphisms in the canine glutamate transporter-1 gene: identification and variation among five dog breeds

Excitatory amino acid transporters (EAATs) are important for terminating glutamatergic neurotransmission and protect central nervous system (CNS) neurons from glutamatergic excitotoxicity. We selected these genes as targets that may relate to canine behavioral traits. After screening four EAAT genes (glutamate transporter-1; GLT-1, excitatory amino acid transporter 4; EAAT4, excitatory amino acid carrier; EAAC1, glutamate/aspartate transporter; GLAST) for single nucleotide polymorphisms (SNPs), we identified two silent SNPs (C129T and T471C) in the GLT-1 gene. We genotyped 193 dogs of 5 breeds and found significant variation among breeds in these two SNPs in GLT-1. The C129T polymorphism was not observed in Malteses and Miniature Schnauzers. These results suggest that polymorphisms in the GLT-1 gene may be useful markers for examining how the genetic background relates to the behavioral traits of dogs.

Canine tyrosine hydroxylase (TH) gene and dopamine beta -hydroxylase (DBH) gene: their sequences, genetic polymorphisms, and diversities among five different dog breeds

Dopamine and noradrenaline are catecholamine neurotransmitters that are produced by biosynthetic enzymes such as tyrosine hydroxylase (TH) and dopamine beta -hydroxylase (DBH). As a first step to elucidate the genetic background of canine behavioral traits, we selected these genes as targets and sequenced these canine genes, and found that both were highly homologous with those of human beings. Then brain cDNAs derived from ten unrelated Beagles were used to search for polymorphisms in these genes. Four single nucleotide polymorphisms (SNPs) (C97T, G168A, G180A and C264T), one of which (C97T) will cause amino acid substitution in the TH gene, and two SNPs (C789A and A1819G), both of which will cause amino acid substitutions in the DBH gene were identified. The allelic frequencies among five dog breeds (47 Golden Retrievers, 41 Labrador Retrievers, 40 Malteses, 26 Miniature Schnauzers, and 39 Shibas) were examined and found to have significant variation between them with regards to all these SNPs, except for C97T in the TH gene and A1819G in the DBH gene. The polymorphisms of C97T and A1819G were found only in the Shiba. The present results suggest that the polymorphisms of the genes encoding catecholamine biosynthetic enzymes may become important markers for examining the genetic background of behavioral characteristics in dogs.

A Comparison of the Behavioral Profiles of Purebred Dogs in Japan to Profiles of those in the United States and the United Kingdom

To clarify the behavioral profiles of 56 pure breeds of dogs in Japan, 96 small-animal veterinarians participated in a questionnaire survey using the same criteria as in preceding studies conducted in the United States and the United Kingdom. We found significant differences among breeds in all behavioral traits examined. In addition, gender differences were revealed in terms of aggression to dogs, territorial defense, excitability, general activity, dominance over owner, destructiveness, watchdog barking, and snapping at children, which were all rated higher in males than females, whereas obedience training and housebreaking ease were rated higher in females. No gender differences were evident in playfulness, excessive barking, or affection demand. Using factor analyses, "aggressiveness", "reactivity", and "trainability" were determined to be consistent with results found in the US and UK surveys. On the basis of these factor scores, seven groups of breeds were determined by cluster analysis to compare to the US survey; 22 of the 38 breeds common with the US survey were categorized into the same groups as those in that survey. The results demonstrated differences in canine behavioral predisposition among breeds and between genders. The similarity in the results between our study and previous surveys, which involved distinct geographical locales, suggests that the genetic basis of breed-specific temperamental traits is manifested irrespective of the cultural or regional identities of the owners.

Olfactory Receptor Sequence Polymorphism Within and Between Breeds of Dogs

Olfactory receptors, to which odorant molecules specifically bind, are encoded by the largest gene family yet identified in the mammalian genome. We investigated additional polymorphism due to the possible existence of multiple alleles dispersed in different dog breeds by carrying out a survey of the sequences of 16 olfactory receptor genes in a sample of 95 dogs of 20 different breeds. The level of polymorphism was high--all genes were found to have allelic variants--leading to amino acid changes and pseudogenization of some alleles in a number of cases. This preliminary study also revealed that some alleles are breed specific (or rare in the dog population), with some representing the major allele in the breeds concerned.

Molecular and pharmacological characterization of serotonin 5-HT2A and 5-HT2B receptor subtypes in dog

We report the cloning, molecular characterization, and pharmacological characterization of the canine 5-HT2A and 5-HT2B receptors. The canine and human 5-HT2A receptors share 93% amino acid homology. The canine and human 5-HT2B receptors are also highly conserved (87% homology) with the exception of the carboxyl termini where the canine protein is 62 amino acids shorter. Both the canine 5-HT2A and 5-HT2B receptors have high affinity for [3H]5-HT (KD=4.50+/-0.89 nM and 3.10+/-0.82 nM, respectively) and, in general, the pharmacology of these two receptors matches closely the pharmacology of their human homologs for the 19 serotonergic ligands tested. However, the functional response (Ca2+ mobilization) of the canine 5-HT2B receptor to several agonists was weaker compared to the human 5-HT2B receptor. Using quantitative reverse transcriptase polymerase chain reaction, a high expression level of canine 5-HT2A receptor mRNA was detected in the brain and lower levels in peripheral tissues, whereas the highest levels of canine 5-HT2B receptor mRNA were observed in lungs and smooth muscles. A significant level of canine 5-HT2B receptor mRNA was detected in brain tissue. The availability of the full sequence and pharmacology of the canine 5-HT2A and canine 5-HT2B receptors provides useful information for the interpretation of previous and future pharmacological studies of 5-HT2A/2B ligands in dog.