Validation of genetic variants associated with early acute rejection in kidney allograft transplantation.

Numerous reports have identified genetic variants associated with kidney transplant outcome, but only a few have been validated in subsequent studies. We analyzed the association of 21 previously reported genetic variants associated with acute rejection (AR), in an effort to validate these associations in our kidney transplant population. All recipients (n = 585) received Ab induction, rapid discontinuation of prednisone, and calcineurin inhibitors with either mycophenolate mofetil or sirolimus. Both univariate analysis and logistic regression were used for determining the association between the genotypes and AR. Univariate analysis detected one significant single-nucleotide polymorphism (p = 0.03), rs1801133, within the methylenetetrahydrofolate reductase (MTHFR) gene associated with AR. Logistic regression analysis identified two variants associated with AR, the 32-bp deletion within chemokine (C-C motif) receptor 5 gene (rs333) and the p.222A/V variant (rs1801133) within the MTHFR gene. Although our analysis utilized a much larger cohort than used in previous reports, we were only able to detect an association with two of these variants. The lack of validation for the other 19 variants may be due to the small effect size, or that, they are not associated with AR. These results stress the need for larger cohorts for both future studies as well as for validation studies.

Power of multifactor dimensionality reduction and penalized logistic regression for detecting gene-gene interaction in a case-control study.

BACKGROUND: There is a growing awareness that interaction between multiple genes play an important role in the risk of common, complex multi-factorial diseases. Many common diseases are affected by certain genotype combinations (associated with some genes and their interactions). The identification and characterization of these susceptibility genes and gene-gene interaction have been limited by small sample size and large number of potential interactions between genes. Several methods have been proposed to detect gene-gene interaction in a case control study. The penalized logistic regression (PLR), a variant of logistic regression with L2 regularization, is a parametric approach to detect gene-gene interaction. On the other hand, the Multifactor Dimensionality Reduction (MDR) is a nonparametric and genetic model-free approach to detect genotype combinations associated with disease risk. METHODS: We compared the power of MDR and PLR for detecting two-way and three-way interactions in a case-control study through extensive simulations. We generated several interaction models with different magnitudes of interaction effect. For each model, we simulated 100 datasets, each with 200 cases and 200 controls and 20 SNPs. We considered a wide variety of models such as models with just main effects, models with only interaction effects or models with both main and interaction effects. We also compared the performance of MDR and PLR to detect gene-gene interaction associated with acute rejection(AR) in kidney transplant patients. RESULTS: In this paper, we have studied the power of MDR and PLR for detecting gene-gene interaction in a case-control study through extensive simulation. We have compared their performances for different two-way and three-way interaction models. We have studied the effect of different allele frequencies on these methods. We have also implemented their performance on a real dataset. As expected, none of these methods were consistently better for all data scenarios, but, generally MDR outperformed PLR for more complex models. The ROC analysis on the real dataset suggests that MDR outperforms PLR in detecting gene-gene interaction on the real dataset. CONCLUSION: As one might expect, the relative success of each method is context dependent. This study demonstrates the strengths and weaknesses of the methods to detect gene-gene interaction.

The R402Q tyrosinase variant does not cause autosomal recessive ocular albinism.

Mutations in the gene for tyrosinase, the key enzyme in melanin synthesis, are responsible for oculocutaneous albinism type 1, and more than 100 mutations of this gene have been identified. The c.1205G > A variant of the tyrosinase gene (rs1126809) predicts p.R402Q and expression studies show thermolabile enzyme activity for the variant protein. The Q402 allele has been associated with autosomal recessive ocular albinism when it is in trans with a tyrosinase gene mutation associated with oculocutaneous albinism type 1. We have identified 12 families with oculocutaneous albinism type 1 that exhibit segregation of the c.1205G > A variant with a known pathologic mutation on the homologous chromosome, and demonstrate no genetic association between autosomal recessive oculocutaneous albinism and the Q402 variant. We conclude that the codon 402 variant of the tyrosinase gene is not associated with albinism.

Variations in the catechol O-methyltransferase polymorphism and prefrontally guided behaviors in adolescents.

BACKGROUND: The catechol-O-methyltransferase (COMT) gene codes for an enzyme that degrades prefrontal cortex (PFC) synaptic dopamine. Of two identified alleles (Met and Val), the Met allele results in COMT activity that is up to 4 times less pronounced than that conferred by the Val allele, resulting in greater PFC dopamine concentrations. Met-Met homozygotes perform better than individuals who possess the Val allele on PFC-mediated cognitive tasks. These genotypic variations and their associations with executive functions have been described in adults and prepubescent children, but there is a paucity of research assessing these relations in adolescent samples. METHODS: In this study, 70 children aged 9-17 were genotyped for COMT and completed measures of working memory, attention, fine motor coordination, and motor speed. RESULTS: COMT genotype modulated all but the motor speed measures. The Val-Met genotype was optimal for performance in this adolescent sample. CONCLUSIONS: Results are discussed within the context of developmental changes in the dopaminergic system during adolescence.

Differentially expressed gene transcripts using RNA sequencing from the blood of immunosuppressed kidney allograft recipients.

We performed RNA sequencing (RNAseq) on peripheral blood mononuclear cells (PBMCs) to identify differentially expressed gene transcripts (DEGs) after kidney transplantation and after the start of immunosuppressive drugs. RNAseq is superior to microarray to determine DEGs because it's not limited to available probes, has increased sensitivity, and detects alternative and previously unknown transcripts. DEGs were determined in 32 adult kidney recipients, without clinical acute rejection (AR), treated with antibody induction, calcineurin inhibitor, mycophenolate, with and without steroids. Blood was obtained pre-transplant (baseline), week 1, months 3 and 6 post-transplant. PBMCs were isolated, RNA extracted and gene expression measured using RNAseq. Principal components (PCs) were computed using a surrogate variable approach. DEGs post-transplant were identified by controlling false discovery rate (FDR) at < 0.01 with at least a 2 fold change in expression from pre-transplant. The top 5 DEGs with higher levels of transcripts in blood at week 1 were TOMM40L, TMEM205, OLFM4, MMP8, and OSBPL9 compared to baseline. The top 5 DEGs with lower levels at week 1 post-transplant were IL7R, KLRC3, CD3E, CD3D, and KLRC2 (Striking Image) compared to baseline. The top pathways from genes with lower levels at 1 week post-transplant compared to baseline, were T cell receptor signaling and iCOS-iCOSL signaling while the top pathways from genes with higher levels than baseline were axonal guidance signaling and LXR/RXR activation. Gene expression signatures at month 3 were similar to week 1. DEGs at 6 months post-transplant create a different gene signature than week 1 or month 3 post-transplant. RNAseq analysis identified more DEGs with lower than higher levels in blood compared to baseline at week 1 and month 3. The number of DEGs decreased with time post-transplant. Further investigations to determine the specific lymphocyte(s) responsible for differential gene expression may be important in selecting and personalizing immune suppressant drugs and may lead to targeted therapies.

Tyrosinase gene mutations in oculocutaneous albinism 1 (OCA1): definition of the phenotype.

Oculocutaneous albinism (OCA) is a common human genetic condition resulting from mutations in at least twelve different genes. OCA1 results from mutations of the tyrosinase gene and presents with the life-long absence of melanin pigment after birth (OCA1A) or with the development of minimal-to-moderate amounts of cutaneous and ocular pigment (OCA1B). Other types of OCA have variable amounts of cutaneous and ocular pigment. We hypothesized that white hair at birth indicates OCA1 and tested this in a sample of 120 probands with OCA and white hair at birth. We found that 102 (85%) of the probands had OCA1 with one or two identifiable tyrosinase gene mutations, with 169 (83%) of the 204 OCA1 tyrosinase gene alleles having identifiable mutations and 35 (17%) having no identifiable change in the coding, splice junction, or proximal promoter regions of the gene. The inability to identify the mutation was more common with OCA1B (24/35, 69%) than with OCA1A (11/35, 31%) alleles. Seven probands with no tyrosinase gene mutations were found to have OCA2 with one or two P gene mutations, and in eleven, no mutations were detected in either gene. We conclude that (1) the presence of white hair at birth is a useful clinical tool suggesting OCA1 in a child or adult with OCA, although OCA2 may also have this presentation; (2) the molecular analysis of the tyrosinase and P genes are necessary for precise diagnosis; and (3) the presence of alleles without identifiable mutations of the tyrosinase gene, particularly in OCA1B, suggests that more complex mutation mechanisms of this gene are common in OCA.

MC1R mutations modify the classic phenotype of oculocutaneous albinism type 2 (OCA2).

The heterogeneous group of disorders known as oculocutaneous albinism (OCA) shares cutaneous and ocular hypopigmentation associated with common developmental abnormalities of the eye. Mutations of at least 11 loci produce this phenotype. The majority of affected individuals develop some cutaneous melanin; this is predominantly seen as yellow/blond hair, whereas fewer have brown hair. The OCA phenotype is dependent on the constitutional pigmentation background of the family, with more OCA pigmentation found in families with darker constitutional pigmentation, which indicates that other genes may modify the OCA phenotype. Sequence variation in the melanocortin-1 receptor (MC1R) gene is associated with red hair in the normal population, but red hair is unusual in OCA. We identified eight probands with OCA who had red hair at birth. Mutations in the P gene were responsible for classic phenotype of oculocutaneous albinism type 2 (OCA2) in all eight, and mutations in the MC1R gene were responsible for the red (rather than yellow/blond) hair in the six of eight who continued to have red hair after birth. This is the first demonstration of a gene modifying the OCA phenotype in humans.