Nuclear receptor NR4A2 IVS6 +18insG and brain derived neurotrophic factor (BDNF) V66M polymorphisms and risk of Taiwanese Parkinson's disease

Two novel heterozygous truncating variants in NR4A2 identified in patients with neurodevelopmental disorder and brief literature review

Pathogenic variants in the nuclear receptor superfamily 4 group A member 2 (NR4A2) cause an autosomal dominant neurodevelopmental disorder with or without seizures. Here, we described two patients presenting with developmental delay, language impairment, and attention-deficit hyperactivity disorder. Trio-based whole exome sequencing revealed two novel heterozygous variants, c.1541-2A > C and c.915C > A, in NR4A2. Both variants were identified as de novo and confirmed by Sanger sequencing. In vitro functional analyses were performed to assess their effects on expression of mRNA or protein. The canonical splicing variant c.1541-2A > C caused aberrant splicing, leading to the retention of intron 7 and a truncated protein due to an early termination codon within intron 7 with decreased protein expression, while the variant c.915C > A was shown to result in a shorter protein with increased expression level unexpectedly. The clinical and genetic characteristics of the previously published patients were briefly reviewed for highlighting the potential link between mutations and phenotypes. Our research further confirms that NR4A2 is a disease-causing gene of neurodevelopmental disorders and suggests alterations in different domains of NR4A2 cause various severity of symptoms.

Structural, molecular hybridization and network based identification of miR-373-3p and miR-520e-3p as regulators of NR4A2 human gene involved in neurodegeneration

MicroRNAs (miRNAs) are short non-coding RNAs with a 22 nucleotide sequence length and docks to the 3'UTR/5'UTR of the gene to regulate their mRNA translation to play a vital role in neurodegenerative diseases. The Nuclear Receptor gene (NR4A2), a transcription factor, and a steroid-thyroid hormone retinoid receptor is involved in neural development, memory formation, dopaminergic neurotransmission, and cellular protection from inflammatory damage. Therefore, recognizing the miRNAs is essential to efficiently target the 3'UTR/5'UTR of the NR4A2 gene and regulate neurodegeneration. Highly stabilized top miRNA-mRNA hybridized structures, their homologs, and identification of the best structures based on their least free energy were evaluated using in silico techniques. The miR-gene, gene-gene network analysis, miR-disease association, and transcription factor binding sites were also investigated. Results suggest top 166 miRNAs targeting the NR4A2 mRNA, but with a total of 10 miRNAs bindings with 100% seed sequence identity (both at 3' and 5'UTR) at the same position on the NR4A2 mRNA region. The miR-373-3p and miR-520e-3p are considered the best candidate miRNAs hybridizing with high efficiency at both 3' and 5'UTR of NR4A2 mRNA. This could be due to the most significant seed sequence length complementary, supplementary pairing, and absence of non-canonical base pairs. Furthermore, the miR-gene network, target gene-gene interaction analysis, and miR-disease association provide an understanding of the molecular, cellular, and biological processes involved in various pathways regulated by four transcription factors (PPARG, ZNF740, NRF1, and RREB1). Therefore, miR-373-3p, 520e-3p, and four transcription factors can regulate the NR4A2 gene involved in the neurodegenerative process.

Association of genetic variants within HLA-DR region with Parkinson's disease in Taiwan

Previous genome-wide association studies in Caucasians suggest genetic loci of human leukocyte antigen (HLA)-DR region may be associated with Parkinson's disease (PD). However, these gene-disease associations were limitedly reported in Asian populations. Herein, we investigated the effects of 5 top PD-associated genetic variants within HLA-DR region in Caucasians, including rs4248166, rs9268515, rs2395163, rs75855844, and rs660895, by genotyping 486 Taiwanese patients with PD and 473 age-matched control subjects. Although the association between rs2395163 C allele and patients with PD demonstrated marginal significance (odds ratio [OR] = 0.74, 95% CI: 0.55-0.99, p = 0.045). The frequency of rs2395163 C allele (8.65%) in male patients with PD was significantly lower than in male control subjects (14.02%; OR = 0.58, 95% CI: 0.39-0.88, p = 0.009). The genetic associations between patients with PD and other tested genetic variants were negative. Although strong linkage disequilibrium (rs4248166-rs9626515-s2395163 and rs9626515-rs660895) were observed, the haplotype analysis did not find any significant risk-associated allelic combinations. These results suggest a distinct genetic background within HLA-DR region between Taiwanese and Caucasian patients with PD.

BDNF Polymorphism: A Review of Its Diagnostic and Clinical Relevance in Neurodegenerative Disorders

Brain-derived neurotrophic factor (BDNF) has a unique role in the neuronal development, differentiation, and survival in the developing and adult nervous system. A common single-nucleotide polymorphism in the pro-region of the human BDNF gene, resulting in a valine to methionine substitution (Val66Met), has been associated with the susceptibility, incidence, and clinical features of several neurodegenerative disorders. Much research has been dedicated to evaluating the effects of polymorphism in the past decade, and functional effects of this genetic variation. A better understanding of how this naturally occurring polymorphism associates with or influences physiology, anatomy, and cognition in both healthy and diseased adults in neurodegenerative conditions will help understand neurochemical mechanisms and definable clinical outcomes in humans. Here we review the role and relevance of the BDNF Val66Met polymorphism in neurodegenerative diseases, with particular emphasis on glaucoma, multiple sclerosis (MS), Alzheimer’s disease (AD) and Parkinson’s disease (PD). Several controversies and unresolved issues, including small effect sizes, possible ethnicity, gender, and age effects of the BDNF Val66Met are also discussed with respect to future research.

DLG2, but not TMEM229B, GPNMB, and ITGA8 polymorphism, is associated with Parkinson's disease in a Taiwanese population

Transmembrane or membrane-associated protein dysfunction is increasingly recognized as an important mechanism of pathogenesis in Parkinson's disease (PD). Previous genome-wide association studies and their meta-analysis in PD genes have identified several risk foci in transmembrane protein-encoding genes. Herein, we investigated the effect of 4 such PD-associated genetic variants reported in Caucasians, including discs-large membrane-associated guanylate kinase scaffolding protein 2 (DLG2 rs3793947), transmembrane protein 229B (TMEM229B rs1555399), glycoprotein nonmetastatic melanoma protein B (GPNMB rs199347), and integrin subunit alpha 8 (ITGA8 rs7077361). A total of 1185 Taiwanese subjects comprising 592 PD patients and 593 unrelated age-matched controls were genotyped. DLG2 rs3793947 AA genotype showed a significantly lower prevalence in female PD patients compared to the female controls (p = 0.019). The recessive model analysis also demonstrated a reduced PD risk for females in AA genotype (odds ratio = 0.573, 95% confidence interval: 0.379-0.868, p = 0.008). The frequencies of TMEM229B rs1555399 and GPNMB rs199347 genotypes and alleles were similar in PD patients and controls. ITG8 rs7077361 was not polymorphic in all subjects of this study. These data suggested that DLG2, but not TMEM229B, GPNMB, and ITGA8, influenced the risk of PD in Taiwan.

Possible genes responsible for developmental delay observed in patients with rare 2q23q24 microdeletion syndrome: Literature review and description of an additional patient

Cases of 2q23q24 microdeletion syndrome are rare. Patients with chromosomal deletions in this region often show language impairment and/or developmental delay of variable severity. Previous genotype-phenotype correlation study suggested GALNT13 and KCNJ3 as possible candidate genes for such phenotypes. We identified a new overlapping deletion in a patient with severe developmental delay. The identified deletion extended toward the distal 2q24.1 region, and more severe phenotypes in the present patient were considered to be related to the additionally deleted genes including NR4A2 and GPD2. Previously reported chromosomal translocation and the mutation identified in GPD2 suggested that this gene would be responsible for the developmental delay. Re-evaluation for the critical region for behavior abnormalities commonly observed in the patients with overlapping deletions of this region suggested that KCNJ3 rather than GALNT13 may be responsible for abnormal behaviors, although there was phenotypic variability. Combinatory deletions involving KCNJ3 and GPD2 may lead to more severe developmental delay. Further studies would be necessary to establish clearer genotype-phenotype correlation in patients with 2q23q24 microdeletion syndrome.

Association of polymorphisms and reduced expression levels of the NR4A2 gene with Parkinson's disease in a Mexican population

INTRODUCTION

The NR4A2 transcription factor is important in the development, survival and phenotype of dopaminergic neurons and it is postulated as a possible biomarker for Parkinson's disease (PD). Therefore, our aim was to analyze in a sample of a Mexican population with idiopathic PD, mutations (in two hotspot mutation regions) and two polymorphisms (rs34884856 in promotor and rs35479735 intronic regions) of the NR4A2 gene. We also evaluate the levels of NR4A2 gene expression in peripheral blood for a Mexican population, and identify whether they are associated with NR4A2 gene polymorphisms.

METHODS

We conducted a case-control study, which included 227 idiopathic PD cases and 454 unrelated controls. Genetic variants of the NR4A2 gene were genotyped by high-resolution melting (HRM) and validated by an automated sequencing method. The gene expression was performed in peripheral blood using a real-time polymerase chain reaction.

RESULTS

The rs35479735 polymorphism was associated with a higher risk of developing PD. In addition, NR4A2 gene expression was significantly decreased in patients with PD. Linkage disequilibrium analysis showed a haplotype H4 (3C-3G) that showed lower levels of expression, and contained the risk alleles for both polymorphisms.

CONCLUSIONS

In summary, this is the first study in a Mexican population that considers the analysis of NR4A2 in patients with PD. An association was identified between genotype and mRNA expression levels of NR4A2 in patients with PD. These results suggest that polymorphisms and expression of the NR4A2 gene could play an important role in the risk of developing PD in Mexican populations.

NR4A2 genetic variation and Parkinson's disease: Evidence from a systematic review and meta-analysis

INTRODUCTION

The homo sapiens nuclear receptor subfamily 4, group A (NR4A2) genetic variation has been implicated as a risk factor for Parkinson's disease (PD). Nevertheless, the results are inconclusive. We conducted a comprehensive systematic review and meta-analysis to quantify the impact of NR4A2 variation on the risk of PD.

METHODS

All eligible case-control studies published up to June 2016 by searching Pubmed, OVID, EBSCO, PsycINFO, ISI Web of Knowledge, Chinese Biomedical Literature Database and China Academic Journals Database were identified. Pooled odds ratio (OR) with 95% confidence interval (CI) were used to access the strength of the association in fixed- or random-effects model.

RESULTS

Eighteen studies reported 24 genetic variants with a total of 6150 cases and 5919 controls were included. Twelve studies for NR4A2 rs35479735 polymorphism and 4 studies for rs12803 were available for meta-analysis. A significant association was observed for rs35479735 under the homozygous model (OR=1.31, 95% CI: 1.10-1.56, P=0.003), whereas no significant association for rs12803 was detected. In subgroup analysis stratified by ethnicity, age onset and familial history, we found no significant association except one in sporadic PD subgroup under the recessive (OR=3.30, 95% CI: 1.23-8.84, P=0.02) and homozygous model (OR=3.43, 95% CI: 1.26-9.33, P=0.02) for rs35479735.

CONCLUSION

The study comprehensively evaluated the association of NR4A2 variation with PD, and the results failed to demonstrate that the NR4A2 polymorphisms significantly associated with PD except for rs35479735, suggesting that more studies are needed to elucidate if NR4A2 is a risk of PD.

Efficient and biologically relevant consensus strategy for Parkinson's disease gene prioritization

BACKGROUND

The systemic information enclosed in microarray data encodes relevant clues to overcome the poorly understood combination of genetic and environmental factors in Parkinson's disease (PD), which represents the major obstacle to understand its pathogenesis and to develop disease-modifying therapeutics. While several gene prioritization approaches have been proposed, none dominate over the rest. Instead, hybrid approaches seem to outperform individual approaches.

METHODS

A consensus strategy is proposed for PD related gene prioritization from mRNA microarray data based on the combination of three independent prioritization approaches: Limma, machine learning, and weighted gene co-expression networks.

RESULTS

The consensus strategy outperformed the individual approaches in terms of statistical significance, overall enrichment and early recognition ability. In addition to a significant biological relevance, the set of 50 genes prioritized exhibited an excellent early recognition ability (6 of the top 10 genes are directly associated with PD). 40 % of the prioritized genes were previously associated with PD including well-known PD related genes such as SLC18A2, TH or DRD2. Eight genes (CCNH, DLK1, PCDH8, SLIT1, DLD, PBX1, INSM1, and BMI1) were found to be significantly associated to biological process affected in PD, representing potentially novel PD biomarkers or therapeutic targets. Additionally, several metrics of standard use in chemoinformatics are proposed to evaluate the early recognition ability of gene prioritization tools.

CONCLUSIONS

The proposed consensus strategy represents an efficient and biologically relevant approach for gene prioritization tasks providing a valuable decision-making tool for the study of PD pathogenesis and the development of disease-modifying PD therapeutics.

Challenges and promises in the development of neurotrophic factor-based therapies for Parkinson's disease

Parkinson's disease (PD) is a chronic movement disorder typically coupled to progressive degeneration of dopaminergic neurons in the substantia nigra (SN). The treatments currently available are satisfactory for symptomatic management, but the efficacy tends to decrease as neuronal loss progresses. Neurotrophic factors (NTFs) are endogenous proteins known to promote neuronal survival, even in degenerating states. Therefore, the use of these factors is regarded as a possible therapeutic approach, which would aim to prevent PD or to even restore homeostasis in neurodegenerative disorders. Intriguingly, although favorable results in in vitro and in vivo models of the disease were attained, clinical trials using these molecules have failed to demonstrate a clear therapeutic benefit. Therefore, the development of animal models that more closely reproduce the mechanisms known to underlie PD-related neurodegeneration would be a major step towards improving the capacity to predict the clinical usefulness of a given NTF-based approach in the experimental setting. Moreover, some adjustments to the design of clinical trials ought to be considered, which include recruiting patients in the initial stages of the disease, improving the efficacy of the delivery methods, and combining synergetic NTFs or adding NTF-boosting drugs to the already available pharmacological approaches. Despite the drawbacks on the road to the use of NTFs as pharmacological tools for PD, very relevant achievements have been reached. In this article, we review the current status of the potential relevance of NTFs for treating PD, taking into consideration experimental evidence, human observational studies, and data from clinical trials.

BDNF promoter I methylation correlates between post-mortem human peripheral and brain tissues

Several psychiatric disorders have been associated with CpG methylation changes in CG rich promoters of the brain-derived neurotrophic factor (BDNF) mainly by extracting DNA from peripheral blood cells. Whether changes in peripheral DNA methylation can be used as a proxy for brain-specific alterations remains an open question. In this study we aimed to compare DNA methylation levels in BDNF promoter regions in human blood cells, muscle and brain regions using bisulfite-pyrosequencing. We found a significant correlation between the levels of BDNF promoter I methylation measured in quadriceps and vPFC tissues extracted from the same individuals (n = 98, Pearson, r = 0.48, p = 4.5 × 10(-7)). In the hippocampus, BDNF promoter I and IV methylation levels were strongly correlated (Pearson, n = 37, r = 0.74, p = 1.4 × 10(-7)). We found evidence for sex-dependent effect on BDNF promoter methylation levels in the various tissues and blood samples. Taken together, these data indicate a strong intra-individual correlation between peripheral and brain tissue. They also suggest that sex determines methylation patterns in BDNF promoter region across different types of tissue, including muscle, brain, and blood.

NURR1 in Parkinson disease--from pathogenesis to therapeutic potential

In Parkinson disease (PD), affected midbrain dopamine (DA) neurons lose specific dopaminergic properties before the neurons die. How the phenotype of DA neurons is normally established and the ways in which pathology affects the maintenance of cell identity are, therefore, important considerations. Orphan nuclear receptor NURR1 (NURR1, also known as NR4A2) is involved in the differentiation of midbrain DA neurons, but also has an important role in the adult brain. Emerging evidence indicates that impaired NURR1 function might contribute to the pathogenesis of PD: NURR1 and its transcriptional targets are downregulated in midbrain DA neurons that express high levels of the disease-causing protein α-synuclein. Clinical and experimental data indicate that disrupted NURR1 function contributes to induction of DA neuron dysfunction, which is seen in early stages of PD. The likely involvement of NURR1 in the development and progression of PD makes this protein a potentially interesting target for therapeutic intervention.

Nur-related receptor 1 gene polymorphisms and alcohol dependence in Mexican Americans

AIM: To investigate the association of polymorphisms of nur-related receptor 1 (Nurr1) and development of alcohol dependence in Mexican Americans.

METHODS: Peripheral blood samples were collected from 374 alcoholic and 346 nonalcoholic Mexican Americans; these two groups were sex- and age-matched. Sample DNA was extracted and genomic DNA was amplified by polymerase chain reaction. The -2922(C) 2-3 polymerase chain reaction products were digested with Sau96I, alleles of 1345(G/C), and -1198(C/G) in the regulatory region as well as Ex+132 (G/T/A/C) and Ex+715(T/-) in exon 3 were studied by sequencing.

RESULTS: The C2/C2, C2/C3, C3/C3 genotype distribution of -2922(C) 2-3 was 34.4%, 38.2% and 27.5% in the nonalcoholic group compared to 23.3%, 51.2% and 25.4% in the alcoholic group (P = 0.001). The C/C, C/G, G/G genotype distribution of -1198(C/G) was 23.5%, 46.1% and 30.3% in the nonalcoholic group compared to 13.9%, 50.9% and 35.3% in the alcoholic group (P = 0.007). However, the -1345 (G/C), Ex3+132(G/T/A/C) and Ex3+715(T/-) alleles were not polymorphic in Mexican Americans, and all those studied had G/G, G/G and T/T genotype for these three alleles, respectively. The -2922(C) 2-3 did not show allele level difference between alcoholic and nonalcoholic individuals, but -1198 (C/G) showed a significant allele frequency difference between alcoholic (39.3%) and nonalcoholic (46.6%) populations (P = 0.005). Excluding obese individuals, significant differences were found at both genotypic and allelic levels for the -2922(C) 2-3 polymorphism (P = 0.000 and P = 0.049) and the -1198 (C/G) polymorphism (P = 0.008 and P = 0.032) between nonobese alcoholics and nonobese controls. Excluding smokers, a significant difference was found only at the genotypic level for the -2922(C) 2-3 polymorphism (P = 0.037) between nonsmoking alcoholics and nonsmoking controls, but only at the allelic level for the -1198(C/G) polymorphism (P = 0.034).

CONCLUSION: Polymorphisms in the regulatory region of Nurr1 are implicated in pathogenesis of alcohol dependence and the Nurr1/dopamine signaling pathway might be important for this dependence development in Mexican Americans.

Brain-derived neurotrophic factor (BDNF) genetic polymorphism greatly increases risk of leucine-rich repeat kinase 2 (LRRK2) for Parkinson's disease

Parkinson's disease (PD) is a complex neurodegenerative disorder. Although the p.G2385R allele of leucine-rich repeat kinase 2 (LRRK2) has been recently reported as a common genetic variant that increases the risk for typical PD exclusively among Asian population, its genetic modifiers is yet to be studied. Brain-derived neurotrophic factor (BDNF) has been shown to play an important role in the survival of dopaminergic neurons and its genetic polymorphism was associated with an increased risk for PD at an older age onset. The current case-control study was performed to investigate the interaction between LRRK2 p.G2385R and BDNF p.V66M in a Chinese PD cohort. A total of 464 PD patients and 549 controls were involved in this study. LRRK2 p.G2385R variant (odds ratio [OR] = 3.2; 95% confidence interval [CI] = 1.96-5.15, p < 0.0001), not BDNF p.V66M alone significantly increased the risk of PD. However, the simultaneous presence of both LRRK2 and BDNF variants significantly enhanced the risk for PD (OR = 4.033; 95% CI = 2.188-7.435, p < 0.0001), particularly in patients with an onset age of older than 60 (OR = 6.439; 95% CI = 3.096-13.389, p < 0.0001). Our results further support that LRRK2 variants are an independent genetic risk factor for typical PD, but BDNF variants can greatly increase LRRK2-induced risk for patients with an onset age of older than 60 indicating an additive effect between the 2 genes, which might aid in studying the mechanism underlying LRRK2 parkinsonism and developing potential therapeutic strategies.

Non-synonymous single-nucleotide polymorphisms associated with blood pressure and hypertension

In this study, we determined the association of 1180 non-synonymous single-nucleotide polymorphisms (SNPs) with systolic blood pressure (SBP) and hypertensive status. A total of 8842 subjects were taken from two community-based cohorts--Ansung (n=4183) and Ansan (n=4659), South Korea--which had been established for genome-wide association studies (GWAS). Five SNPs (rs16835244, rs2286672, rs6265, rs17237198 and rs7312017) were significantly associated (P-values: 0.003-0.0001, not corrected for genome-wide significance) with SBP in both cohorts. Of these SNPs, rs16835244 and rs2286672 correlated with risk for hypertension. The rs16835244 SNP replaces Ala288 in arginine decarboxylase (ADC) with serine, and rs2286672 replaces Arg172 in phospholipase D2 (PLD2) with cysteine. A comparison of peptide sequences between vertebrate homologues revealed that the SNPs identified occur at conserved amino-acid residues. In silico analysis of the protein structure showed that the substitution of a polar residue, serine, for a non-polar alanine at amino-acid residue 288 affects a conformational change in ADC, and that Arg172 in PLD2 resides in the PX domain, which is important for membrane trafficking. These results provide insights into the function of these non-synonymous SNPs in the development of hypertension. The study investigating non-synonymous SNPs from GWAS not only by statistical association analysis but also by biological relevance through the protein structure might be a good approach for identifying genetic risk factors for hypertension, in addition to discovering causative variations.

Molecular mechanisms of pathogenesis of Parkinson's disease

Parkinson's disease is a complex disease characterized by a progressive degeneration of nigrostriatal dopaminergic neurons. The development of this condition is defined by the interaction between the genetic constitution of an organism and environmental factors. Analysis of the genes associated with development of monogenic forms of disease has allowed pointing out several mechanisms involved in Parkinson's disease pathogenesis such as the ubiquitin-proteasome degradation, differentiation of dopaminergic neurons, mitochondrial dysfunction, oxidative damage, and others. In this review, a variety of data which throw light on molecular mechanisms underlying pathogenesis of Parkinson's disease will be considered.

Examination of the MSX1 gene in patients with Parkinson's disease

BACKGROUND

Several genetic variants in transcription factor genes have been reported to be associated with Parkinson's disease (PD). The muscle segment homeobox drosophila homolog of 1 gene (MSX1) is a major upstream regulator of the dopaminergic neuronal subtype specification.

AIMS OF THE STUDY

To determine whether genetic variation in the coding region of the MSX1 gene plays a role in the etiology of PD.

METHODS

We searched for genetic variations in the coding region of the MSX1 gene in 202 patients with PD and 200 normal controls by PCR-single-strand conformation polymorphism (PCR-SSCP) and sequencing.

RESULTS

No mutation in the MSX1 gene was identified in our cohort.

CONCLUSIONS

Mutations in the coding region of the MSX1 gene play little or no role in the development of PD.

Brain-derived neurotrophic factor in neurodegenerative diseases

Changes in the levels and activities of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), have been described in a number of neurodegenerative disorders, including Huntington disease, Alzheimer disease and Parkinson disease. It is only in Huntington disease, however, that gain-of-function and loss-of-function experiments have linked BDNF mechanistically with the underlying genetic defect. Altogether, these studies have led to the development of experimental strategies aimed at increasing BDNF levels in the brains of animals that have been genetically altered to mimic the aforementioned human diseases, with a view to ultimately influencing the clinical treatment of these conditions. In this article, we will review the current knowledge about the involvement of BDNF in a number of neurodegenerative diseases, with particular emphasis on Huntington disease, and will provide the rationale for and discuss the problems in proposing BDNF treatment as a beneficial and feasible therapeutic approach in the clinic.

Mitochondrial DNA polymorphisms and the risk of Parkinson's disease in Taiwan

A critical role of mitochondrial dysfunction has been implicated in the pathogenesis of Parkinson's disease (PD). The association of mitochondrial DNA (mtDNA) polymorphisms 9055G/A, 10398G/A and 13708G/A with PD has been controversial. In this study we analyzed whether these three genetic polymorphisms are associated with PD in a cohort of 416 PD cases and 372 ethnically matched controls. The allele frequency distribution of any of these three analyzed polymorphisms was not significantly different between the cases and the controls. None of the six haplotypes derived influences risk of PD. Notably, after stratification by age, individuals over 70 years of age carrying the haplotype 9055G-10398A-13708G demonstrated a significant decrease in risk of developing PD (OR = 0.44, 95% CI = 0.24-0.80, p = 0.008). These results suggest that the mtDNA haplotype 9055G-10398A-13708G plays a role in PD susceptibility among Taiwanese people older than 70 years of age.