High-throughput genotyping of repeat polymorphism in the regulatory region of serotonin transporter gene by gel microchip electrophoresis

Additive effects of serotonergic and dopaminergic polymorphisms on trait impulsivity

Twin studies suggest 45% heritability of trait impulsivity. Results from candidate gene studies to date are contradictory; impulsivity phenotypes were measured by different behavioral and questionnaire methods related either to the dopaminergic or to the serotonergic system. Here we report an association study of both dopaminergic (COMT rs4680, DRD4 48 bp VNTR, DRD2/ANKK1 rs1800497) and serotonergic (HTR1A rs6925, HTR1B rs13212041, SLC6A4 5-HTTLPR) gene polymorphisms and trait impulsivity assessed with the Barratt Impulsiveness Scale (BIS-11) in a sample of 687 Caucasian young adults. Results showed lower impulsivity in the presence of the DRD4 7-repeat (P = 0.006) and the HTR1B rs13212041 alleles (P = 0.003). These findings stayed significant after Bonferroni correction. A multivariate analysis using Bayesian networks confirmed independent effects of these two polymorphisms and provided a coherent characterization of the system of dependencies with respect to the impulsivity construct as well as its subscales. These results clearly suggest an additive effect of dopaminergic and serotonergic polymorphisms on trait impulsivity.

Analysis of a polymorphic microRNA target site in the purinergic receptor P2RX7 gene

The recent discovery of post-transcriptional regulation by microRNAs (miRNAs) drew our attention to SNPs of putative miRNA target sites in candidate genes of depression-related psychiatric disorders. The P2RX7 (purinergic receptor P2X, ligand-gated ion channel, 7) gene has been suggested as a candidate for major depressive and bipolar disorder, because of repeated associations with the rs2230912 (Gln460Arg) polymorphism. As this polymorphism is located at the end of the coding region, we considered a possible linkage with SNP(s) in putative miRNA target sites of the 3' untranslated region. Based on our in silico search, the rs1653625 fulfilled this criterion. This SNP, however, is surrounded with polycytosine and polyadenine tracts, which hindered its analysis until now. In this study, we describe a readily applicable genotyping method for rs1653625 by applying a primer that introduces mismatched nucleotides to create a restriction enzyme cleavage site. The resulting allele-specific products with 19 base pair difference were separated by both traditional horizontal agarose gel electrophoresis and multicapillary gel electrophoresis. The developed genotyping method was applied in our depression-related association study.

Genetic and environmental influence on attachment disorganization

BACKGROUND

Empirical studies demonstrate that maternal sensitivity is associated with attachment security in infancy, while maternal frightening/frightened behavior is related to attachment disorganization. However, attachment disorganization is also predicted by individual dispositions in infancy. Indeed, recent studies indicate a link between attachment disorganization and DRD4 gene polymorphisms, thus suggesting a genetic vulnerability for attachment disorganization. The aims of our study were twofold, to test a) a possible direct link between molecular genetic variations and attachment disorganization, and b) a possible gene-environment interaction with a moderating effect of early maternal caregiving.

METHODS

Attachment security and disorganization, as well as quality of maternal behavior were assessed in the infants of the Regensburg Longitudinal Study IV (N = 106) at the age of 12 months. DNA samples were collected in order to assess the exon III repeat polymorphism in the coding region and the -521 C/T single nucleotide polymorphism (SNP) in the regulatory region of the DRD4 gene and a repeat polymorphism (5-HTTLPR) in the promoter region of the serotonin transporter gene.

RESULTS

Significant associations were found between attachment disorganization and the short polymorphism of the serotonin transporter gene. Also, a gene-environment interaction indicated that this genetic association was only valid for infants of mothers exhibiting low responsiveness. No other significant genetic associations with attachment disorganization were apparent.

CONCLUSIONS

The study suggests a gene-environment interaction whereby biological determinants of attachment disorganization are moderated by social experiences. Different pathways of the development of attachment disorganization are discussed based on a bio-behavioral model of development.

Electrophoretic microfluidic devices for mutation detection in clinical diagnostics

BACKGROUND

In an era of growing interest in personalized medicine - where ubiquitous patient genotyping holds unprecedented clinical utility - rapid, sensitive and low-cost methodologies will be required for the detection of genetic variants correlative with disease. Electrophoretic microfluidic devices have emerged as a promising platform for such analyses, inherently offering faster analysis, excellent reagent economy, a small laboratory footprint and potentially seamless integration of multiple analytical steps.

OBJECTIVE

Although glass and polymeric microchips have recently been developed for a wide variety of medical applications, this review focuses on their application to the detection of clinically relevant genomic DNA mutations and polymorphisms.

METHOD

Mutation analysis techniques, including direct gene sizing, enzyme-based assays, heteroduplex analysis, single-strand conformational polymorphism analysis, and multiplex, allele-specific and methylation-specific PCR are included.

CONCLUSION

Further development of 'lab-on-a-chip' or 'micro total analysis system' technologies ultimately aims to streamline and miniaturize the entire genetic analysis process, enabling rapid, point-of-care analysis for molecular diagnostics.

Serotonin transporter polymorphism and borderline or antisocial traits among low-income young adults

OBJECTIVES

The short allele of the serotonin transporter linked polymorphic region, 5HTTLPR has been associated with anxiety, major depressive disorder and suicidality. The impulsive self- and other-damaging behaviors seen in borderline personality disorder and antisocial personality disorder also have substantial comorbidity with depression but are associated with more severe environmental stressors. This study tested the hypothesis of an association between the short allele of the 5HTTLPR and borderline or antisocial traits in young adulthood.

METHODS

The 5HTTLPR was genotyped among 96 young adults from low to moderate income families (62 adults without and 34 adults with borderline personality disorder or antisocial personality disorder traits). Traits of borderline and antisocial personality disorders were assessed with the Structured Clinical Interview for Diagnosis-Axis II.

RESULTS

The number of short 5HTTLPR alleles were significantly related to incidence of borderline personality disorder or antisocial personality disorder traits and also to each set of traits independently. Male sex and quality of care in infancy were also associated with incidence of borderline personality disorder and antisocial personality disorder traits but did not account for the association with the short allele. Depressive disorders were not associated with the short allele in this sample.

CONCLUSIONS

Young adults of lower socioeconomic status who carry the short 5HTTLPR allele may be especially vulnerable to developing antisocial or borderline traits by young adulthood.

Validation of a tentative microsatellite marker for the dopamine D4 receptor gene by capillary gel electrophoresis

Two to four-basepair-short tandem repeats (i.e. microsatellites) are broadly utilized as genetic markers for mapping disease loci in whole genome search analyses. Based on their close vicinity on chromosome 11, the D11S1984 microsatellite was anticipated as a tentative marker for the dopamine D4 receptor gene. A capillary gel electrophoresis based genotype analysis method and an in-house made computational tool was developed for the analysis of the D11S1984 microsatellite marker to examine a healthy Hungarian population of n=106. The data obtained did not suggest significant linkage between the D11S1984 marker and the DRD4 gene.

Multicapillary Electrophoresis Analysis of Single-Nucleotide Sequence Variations in the Deoxycytidine Kinase Gene

Background: Investigation of the genetic background of complex traits is the focus of recent interest, as several common diseases or the individual response to treatments of various illnesses have not yet been explored. These studies require the development and implementation of reliable and large-scale genotyping methods. In this report, we introduce an efficient technique based on PCR–restriction fragment length sequence variation technique for the analysis of the −360CG and −201CT single-nucleotide sequence variations in the deoxycytidine kinase gene.

Methods: A multicapillary gel electrophoresis instrument was used for the size determination of the generated DNA fragments. A healthy Hungarian population of 100 individuals was investigated to determine allele and genotype frequencies for the 2 sequence variations of interest.

Results: We found that the occurrence of the minor allele is rather low, i.e., the frequency of both the −360G and −201T variants is 1%.

Conclusions: Our technique can readily facilitate the analysis of these important sequence variations in other ethnic groups to clarify the role of these sequence variations in conjunction with arabinosylcytosine treatment in acute myeloid leukemia.

Contribution of Serotonin Transporter Gene Polymorphisms to Pediatric Migraine

BACKGROUND

The serotonin transporter gene is a promising candidate locus for the genetic susceptibility of migraine.

OBJECTIVE

Two functional polymorphisms of the serotonin transporter gene (5-HTTLPR and STin2) were analyzed to assess whether these variants are associated with pediatric migraine.

METHODS

Eighty-seven Hungarian pediatric migraine patients and 464 controls were genotyped using polymerase chain reaction. Patients suffering from migraine with (n = 38) or without aura (n = 49) were interviewed regarding the clinical symptoms before or during the attacks.

RESULTS

There was no difference between genotype or allele distribution of 5-HTTLPR and STin2 polymorphisms in the entire group of migraineurs and controls. Analysis of subgroups showed an association between STin2 and migraine with aura, as the 12,12 homozygote genotype was overrepresented in this group of patients. Furthermore, similar allele and genotype patterns were found in cases with severe vomiting and abdominal pain.

CONCLUSIONS

These results confirm and extend the association between the STin2 polymorphism of 5-HTT gene and migraine with aura using pediatric probands. Our data also suggest a novel endophenotype for pediatric migraine characterized by excessive vomiting and abdominal pain during the attack.

Human personality dimensions of persistence and harm avoidance associated with DRD4 and 5-HTTLPR polymorphisms

The associations of human personality traits as measured by the Temperament and Character Inventory (TCI) with two genetic polymorphisms, the dopamine D4 receptor (DRD4) gene exon III repeat polymorphism (VNTR) and the serotonin transporter-linked functional polymorphism (5-HTTLPR) are presented in a population of 157 ethnically homogeneous Caucasians. No association was found between Novelty Seeking and the DRD4 VNTR, but male individuals with a 7-repeat allele exhibited significantly lower Persistence scores. The 5-HTTLPR polymorphism itself had no significant effect on any of the temperament dimensions, but a significant DRD4 VNTR x 5-HTTLPR interaction was observed for Harm Avoidance, the subgroup with a s/s 5-HTTLPR, 7-repeat DRD4 genotype showed a higher mean Harm Avoidance score than the other groups. These results are discussed in relation to the recent findings on infant temperament. Association between the DRD4 7-repeat allele and Persistence can be theoretically linked to the 7-repeat allele as a risk factor for attention deficit hyperactivity disorder.

BioMEMS using electrophoresis for the analysis of genetic mutations

Biomedical microelectromechanical systems (BioMEMS) are rapidly emerging in many areas of genetic analysis. These devices demonstrate potential for rapid analysis using modular components capable of sample purification, amplification, mutation discrimination and detection on small, portable point-of-care instruments. Here, various approaches to genetic mutation detection and the modern analysis platform, capillary electrophoresis, will be briefly reviewed. Microfluidic devices will be discussed in relation to fabrication techniques, mutation detection using simple electrophoretic separations, multiplexed designs and modular functionalities, as well as challenges and issues surrounding this technology.