Catechol-O-methyltransferase Val158Met polymorphism and risk of autism spectrum disorders

Abstract

Objective

Autism spectrum disorders (ASD) are a family of childhood-onset neurodevelopmental disorders with complex genetic mechanisms underlying their aetiology. The aim of this case–control study was to evaluate the effect of the catechol-O-methyltransferase (COMT) gene Val158Met polymorphism on ASD risk in a Chinese Han population.

Methods

The COMT gene Val158Met polymorphism was detected by polymerase chain reaction–restriction fragment length polymorphism in children (≤18 years old) with ASD and healthy control subjects.

Results

The frequency of the Val158/Val158 genotype in children with ASD (22/186; 11.8%) was significantly lower than in controls (38/186; 20.4%). When stratifying by select-item scores on the Autism Diagnostic Interview-Revised protocol, it was found that children with ‘current overactivity’ and ‘ever overactivity’ had a significantly lower frequency of the Val158/Val158 genotype than those without. There were no significant associations between the COMT gene Val158Met polymorphism and ASD subtypes.

Conclusions

The COMT gene Val158Met polymorphism may be a biomarker for phenotypic variation in ASD, but these preliminary findings remain tentative, pending replication in larger, independent samples.

Keywords

Catechol-O-methyltransferase autism gene polymorphism

Introduction

Autism spectrum disorders (ASD) describes a group of male-predominant disorders that are characterized by qualitative impairments in social interactions and communication, and restricted, repetitive and stereotyped behaviours and interests, as well as a delay or abnormalities in social interactions, language or imaginative play; such disorders have an onset before 3 years old.¹ ASD has a high prevalence of 10–60 individuals per 10,000.² It is recognized that autism and other disorders within the ASD family share essential clinical and behavioural features, although they differ in severity and age at onset.³ Although the aetiology of ASD is not fully understood, ASD are generally accepted as having a strong genetic basis, and the estimated heritability of these conditions exceeds 90%.^4,5

Catechol-O-methyltransferase (COMT) plays an important role in the catabolism of brain dopamine and norepinephrine. A common biallelic single nucleotide polymorphism involving a valine (Val) to methionine (Met) substitution at codon 158 of the COMT gene (rs4680) has been identified and localized to chromosome 22q11.1–q11.2.^6,7 The Val158 and Met158 alleles of the COMT gene are associated with high and low enzyme activity, respectively.⁸ Homozygosity for the Met158 allele yields a three- to fourfold reduction in COMT activity relative to Val158 homozygotes, with heterozygotes demonstrating intermediate activity.⁹ The association between COMT gene Val158Met polymorphisms and the risk of ASD is controversial and ambiguous.¹⁰ The purpose of this current study was to examine the effect of COMT gene Val158Met polymorphisms on ASD risk in a population of Chinese Han children.

Patients and methods

Study population

Children with ASD from a Chinese Han population were enrolled sequentially from the Department of Psychiatry, First Affiliated Hospital of WenZhou Medical College, WenZhou, Zhejiang Province, China between January 2009 and January 2011 into this population-based, case–control study. All cases met criteria for autism, Asperger’s syndrome or pervasive developmental disorder-not otherwise specified (PDD-NOS) according to the DSM-IV classification system, using a standard research assessment protocol that included the Autism Diagnostic Interview-Revised (ADI-R)¹¹ and the autism diagnostic observation schedule;¹² each case was diagnostically confirmed by clinician consensus. Exclusion criteria for children included:a diagnosis of Rett syndrome or childhood disintegrative disorder; history of serious head injury, encephalitis or tumours; severe mental retardation (intelligence quotient <20); age >18 years. The healthy control subjects were recruited from the same geographic region; these were children attending a clinic for routine examination in the Department of Psychiatry, First Affiliated Hospital of WenZhou Medical College. The healthy control subjects were matched with the patients with ASD for age and sex.

Written informed consent was obtained from the parent(s) or legal guardian(s) of each study participant. The study protocol was approved by the Ethics Committee of the First Affiliated Hospital of WenZhou Medical College (reference no. 20080106A).

Genotyping analysis

Genomic DNA was isolated from 3–5 ml of ethylenediaminetetra-acetic acid (EDTA; 20 g/l) or 4% sodium citrate (citrate 136 mmol/l, sodium 408 mmol/l) anticoagulated venous blood using the QIAamp® DNA Blood Mini Kit (QIAGEN, Hilden, Germany), according to the manufacturer’s instructions, and stored at 4°C until analysis. The COMT gene Val158Met polymorphism was determined using a polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) analysis. Based on the GenBank reference sequence for the COMT gene, the PCR primers were as follows: forward 5′-CCCAGCGGATGGTGGAT-3′ and reverse 5′-CAGGCATGCACACCTTGTC-3′ (Applied Biosystems, Foster City, CA, USA). The PCR reaction was performed with 30 ng of genomic DNA, 0.5 µM of each primer, 100 µM of each dNTP, 1.25 mM of MgCl₂, 5% dimethyl sulphoxide and 1 U Taq DNA polymerase (Bioline USA, Boston, MA, USA). The PCR amplification was carried out after an initial denaturation at 94°C for 4 min, followed by 30 cycles at 94°C for 30 s, 62°C for 30 s and 72°C for 20 s, with a final elongation step at 72°C for 5 min, using an Applied Biosystems® GeneAmp® PCR System 9700 thermal cycler (Applied Biosystems). β-actin was used as an internal control gene and the primers were as follows: forward 5′-GCACCACACCTTCTACAATG-3′ and reverse 5′-TGCTTGCTGATCCACATCTG-3′ (Applied Biosystems).

The amplified PCR products were fractionated on a 3% agarose Tris–borate–EDTA gel (Agarose 1000; Gibco, Rockville, MD, USA) and stained with ethidium bromide for visualization under ultraviolet light. This procedure rendered three bands in heterozygotes (626, 451 and 222 base pairs [bp]) and two bands in homozygotes (Met158/Met158 resulting in 626 and 222 bp; Val158/Val158 resulting in 626 and 451 bp). To confirm the genotyping results, over 10% of PCR-amplified DNA samples were randomly selected by computer and sent for DNA sequencing.

Statistical analyses

All statistical analyses were performed using the SPSS® statistical software package, version 14.0 (SPSS Inc., Chicago, IL, USA) for Windows®. χ²-tests were used to compare the genotype distribution between the two groups of children. The Hardy–Weinberg test of genetic equilibrium was applied using the χ²-test, to ensure that there was no significant difference between observed and expected genotype frequencies. A P-value < 0.05 was considered statistically significant.

Results

The study population included 186 children with ASD and 186 healthy control subjects. The clinical characteristics of all study participants are shown in Table 1. Children with ASD and controls did not differ significantly regarding age, sex, height, weight or handedness. Among the children with 186 ASD, 90 were diagnosed with autism, 54 with Asperger’s syndrome and 42 with PDD-NOS.

Table 1.

Clinical characteristics of Chinese Han children diagnosed with autism spectrum disorders (ASD) and matched healthy control subjects without ASD, included in a study investigating the association between catechol-O-methyltransferase Val158Met polymorphism and risk of ASD.

Characteristic	Patients with ASD n = 186	Control subjects n = 186
Age, years	8.1 ± 4.3	8.2 ± 4.1
Sex, male/female	138/48	141/45
Height, cm	128.1 ± 9.4	129.9 ± 9.7
Weight, kg	28.7 ± 8.3	29.1 ± 8.5
Handedness, right/left	186/0	186/0
ASD subtypes
Autism	90	–
Asperger’s syndrome	54	–
PDD-NOS	42	–

Data presented as mean ± SD or n of patients.

No statistically significant between-group differences (P ≥ 0.05); χ²-test.

PDD-NOS, pervasive developmental disorder-not otherwise specified.

The PCR–RFLP analysis demonstrated that the frequency of the Val158/Val158 genotype in children with ASD (11.8%) was significantly lower than that observed in healthy control subjects (20.4%) (odds ratio [OR] = 0.52, 95% confidence interval [CI] = 0.27, 0.97; P = 0.04) (Table 2). The distribution of the alleles fitted the Hardy–Weinberg equilibrium. When stratifying the children with ASD by select-item scores on the ADI-R, it was found that children with ‘current overactivity’ (OR = 0.21, 95% CI = 0.05, 0.92; P = 0.04) and ‘ever overactivity’ (OR = 0.19, 95% CI = 0.04, 0.87; P = 0.03) had significantly lower frequencies of the Val158/Val158 genotype than those without (Table 3). When stratifying by subtypes of ASD, no significant differences were found in any groups (Table 4).

Table 2.

Genotype and allele frequencies of the catechol-O-methyltransferase Val158Met polymorphism in Chinese Han children diagnosed with autism spectrum disorders (ASD) and healthy control subjects without ASD.

Genotype/allele	Patients with ASD n = 186	Control subjects n = 186	Odds ratio (95% CI)	Statistical significance^a
Genotype
Met158/Met158	63 (33.9)	56 (30.1)	1 (reference)
Val158/Met158	101 (54.3)	92 (49.5)	0.98 (0.62, 1.54)	NS
Val158/Val158	22 (11.8)	38 (20.4)	0.52 (0.27, 0.97)	0.04
Allele
Met allele frequency	227 (61.0)	204 (54.8)	1 (reference)
Val allele frequency	145 (39.0)	168 (45.2)	0.78 (0.58, 1.04)	NS

Data presented as n (%) of patients or alleles.

χ²-test was used to compare the frequencies of genotypes and alleles between patients and controls.

CI, confidence interval; Met, methionine; Val, valine; NS, no statistically significant difference (P ≥ 0.05).

Table 3.

Select-item scores on the Autism Diagnostic Interview-Revised (ADI-R) protocol and the genotype frequency of the catechol-O-methyltransferase Val158Met polymorphism, in Chinese Han children diagnosed with autism spectrum disorders (ASD).

ADI-R item	Score	Patients with ASD n = 186	Met158/Met158			Val158/Met158			Val158/Val158
ADI-R item	Score	Patients with ASD n = 186	n (%)	OR (95% CI)	Statistical significance^a	n (%)	OR (95% CI)	Statistical significance^a	n (%)	OR (95% CI)	Statistical significance^a
Attention to voice	0	38 (20.4)	13 (34.2)	1 (reference)	20 (52.6)	1 (reference)	5 (13.2)	1 (reference)
	1	56 (30.1)	19 (33.9)	0.99 (0.44, 2.25)	NS	31(55.4)	1.05 (0.52, 2.11)	NS	6 (10.7)	0.81 (0.23, 2.86)	NS
	2	92 (49.5)	31 (33.7)	0.98 (0.46, 2.08)	NS	50 (54.3)	1.03 (0.54, 1.96)	NS	11 (12.0)	0.91 (0.30, 2.79)	NS
Direct gaze	0	20 (10.8)	7 (35.0)	1 (reference)	11 (55.0)	1 (reference)	2 (10.0)	1 (reference)
	1	85 (45.7)	29 (34.1)	0.98 (0.37, 2.54)	NS	46 (54.1)	0.98 (0.43, 2.23)	NS	10 (11.8)	1.18 (0.24, 5.79)	NS
	2	81 (43.5)	27 (33.3)	0.95 (0.36, 2.50)	NS	44 (54.3)	0.99 (0.43, 2.25)	NS	10 (12.3)	1.23 (0.25,6.08)	NS
Current repetitive use of objects	0	74 (39.8)	27 (36.5)	1 (reference)	38 (51.4)	1 (reference)	9 (12.2)	1 (reference)
	1	56 (30.1)	19 (33.9)	0.93 (0.47, 1.84)	NS	31 (55.4)	1.08 (0.60, 1.94)	NS	6 (10.7)	0.88 (0.30, 2.62)	NS
	2	56 (30.1)	17 (30.4)	0.83 (0.41, 1.67)	NS	32 (57.1)	1.11 (0.62, 2.00)	NS	7 (12.5)	1.03 (0.36, 2.93)	NS
Ever repetitive use of objects	0	37 (19.9)	13 (35.1)	1 (reference)	20 (54.1)	1 (reference)	4 (10.8)	1 (reference)
	1	39 (21.0)	12 (30.8)	0.88 (0.35, 2.16)	NS	22 (56.4)	1.04 (0.49, 2.22)	NS	5 (12.8)	1.19 (0.29, 4.76)	NS
	2	110 (59.1)	38 (34.5)	0.98 (0.47, 2.04)	NS	59 (53.6)	0.99 (0.53, 1.86)	NS	13 (11.8)	1.09 (0.34, 3.56)	NS
Current compulsions and rituals	0	96 (51.6)	32 (33.3)	1 (reference)	52 (54.2)	1 (reference)	12 (12.5)	1 (reference)
	1	47 (25.3)	15 (31.9)	0.96 (0.47, 1.94)	NS	26 (55.3)	1.02 (0.57, 1.83)	NS	6 (12.8)	1.02 (0.36, 2.89)	NS
	2	43 (23.1)	16 (37.2)	1.12 (0.56, 2.25)	NS	23 (53.5)	0.99 (0.54, 1.81)	NS	4 (9.3)	0.74 (0.23, 2.44)	NS
Ever compulsions and rituals	0	77 (41.4)	25 (32.5)	1 (reference)	43 (55.8)	1 (reference)	9 (11.7)	1 (reference)
	1	44 (23.7)	14 (31.8)	0.98 (0.46, 2.08)	NS	25 (56.8)	1.02 (0.55, 1.88)	NS	5 (11.4)	0.97 (0.31, 3.08)	NS
	2	65 (34.9)	24 (36.9)	1.14 (0.59, 2.18)	0.70	33 (50.8)	0.91 (0.52, 1.59)	NS	8 (12.3)	1.05 (0.38, 2.89)	NS
Current hand and finger mannerisms	0	75 (40.3)	25 (33.3)	1 (reference)	41 (54.7)	1 (reference)	9 (12.0)	1 (reference)
	1	67 (36.0)	24 (35.8)	1.07 (0.56, 2.06)	NS	35 (52.2)	0.96 (0.55, 1.67)	NS	8 (11.9)	0.99 (0.36, 2.73)	NS
	2	44 (23.7)	14 (31.8)	0.95 (0.45, 2.03)	NS	25 (56.8)	1.04 (0.56, 1.93)	NS	5 (11.4)	0.95 (0.30, 3.01)	NS
Ever hand and finger mannerisms	0	48 (25.8)	17 (35.4)	1 (reference)	26 (54.2)	1 (reference)	5 (10.4)	1 (reference)
	1	48 (25.8)	18 (37.5)	1.06 (0.49, 2.30)	NS	24 (50.0)	0.92 (0.47, 1.83)	NS	6 (12.5)	1.20 (0.34, 4.20)	NS
	2	90 (48.4)	28 (31.1)	0.88 (0.44, 1.76)	NS	51 (56.7)	1.05 (0.58, 1.88)	NS	11 (12.2)	1.17 (0.38, 3.57)	NS
Current complex body movements	0	98 (52.7)	33 (33.7)	1 (reference)	53 (54.1)	1 (reference)	12 (12.2)	1 (reference)
	1	45 (24.2)	16 (35.6)	1.06 (0.53, 2.11)	NS	23 (51.1)	0.94 (0.52, 1.73)	NS	6 (13.3)	1.09 (0.38, 3.09)	NS
	2	43 (23.1)	14 (32.6)	0.97 (0.47, 1.99)	NS	25 (58.1)	1.08 (0.59, 1.95)	NS	4 (9.3)	0.76 (0.23, 2.49)	NS
Ever complex body movements	0	80 (43.0)	27 (33.8)	1 (reference)	43 (53.8)	1 (reference)	10 (12.5)	1 (reference)
	1	35 (18.8)	12 (34.3)	1.02 (0.46, 2.23)	NS	19 (54.3)	1.01 (0.52, 1.97)	NS	4 (11.4)	0.91 (0.27, 3.11)	NS
	2	71 (38.2)	24 (33.8)	1.00 (0.53, 1.89)	NS	39 (54.9)	1.02 (0.60, 1.75)	NS	8 (11.3)	0.90 (0.34, 2.41)	NS
Current aggression towards family	0	83 (44.6)	27 (32.5)	1 (reference)	46 (55.4)	1 (reference)	10 (12.0)	1 (reference)
	1	50 (26.9)	18 (36.0)	1.11 (0.55, 2.21)	NS	27 (54.0)	0.97 (0.54, 1.76)	NS	5 (10.0)	0.83 (0.27, 2.57)	NS
	2	53 (28.5)	18 (34.0)	1.04 (0.52, 2.08)	NS	28 (52.8)	0.95 (0.53, 1.71)	NS	7 (13.2)	1.10 (0.39, 3.06)	NS
Ever aggression towards family	0	59 (31.7)	20 (33.9)	1 (reference)	32 (54.2)	1 (reference)	7 (11.9)	1 (reference)
	1	34 (18.3)	12 (35.3)	1.04 (0.45, 2.39)	NS	18 (52.9)	0.98 (0.48, 2.00)	NS	4 (11.8)	0.99 (0.27, 3.63)	NS
	2	93 (50.0)	31 (33.3)	0.98 (0.51, 1.88)	NS	51 (54.8)	1.01 (0.58, 1.75)	NS	11 (11.8)	1.00 (0.37, 2.72)	NS
Current aggression towards others	0	117 (62.9)	41 (35.0)	1 (reference)	60 (51.3)	1 (reference)	16 (13.7)	1 (reference)
	1	46 (24.7)	16 (34.8)	0.99 (0.51, 1.94)	NS	26 (56.5)	1.10 (0.62, 1.95)	NS	4 (8.7)	0.64 (0.20, 2.00)	NS
	2	23 (12.4)	6 (26.1)	0.74 (0.28, 1.96)	NS	15 (65.2)	1.27 (0.62, 2.62)	NS	2 (8.7)	0.64 (0.14, 2.96)	NS
Ever aggression towards others	0	100 (53.8)	36 (36.0)	1 (reference)	51 (51.0)	1 (reference)	13 (13.0)	1 (reference)
	1	41 (22.0)	13 (31.7)	0.88 (0.42, 1.83)	NS	24 (58.5)	1.15 (0.63, 2.10)	NS	4 (9.8)	0.75 (0.23, 2.44)	NS
	2	45 (24.2)	14 (31.1)	0.86 (0.42, 1.76)	NS	26 (57.8)	1.13 (0.63, 2.04)	NS	5 (11.1)	0.86 (0.29, 2.54)	NS
Current self- injurious behaviour	0	138 (74.2)	45 (32.6)	1 (reference)	77 (55.8)	1 (reference)	16 (11.6)	1 (reference)
	1	19 (10.2)	6 (31.6)	0.97 (0.36, 2.57)	NS	11 (57.9)	1.04 (0.47, 2.29)	NS	2 (10.5)	0.91 (0.19, 4.26)	NS
	2	29 (15.6)	12 (41.4)	1.27 (0.60, 2.69)	NS	13 (44.8)	0.80 (0.39, 1.64)	NS	4 (13.8)	1.19 (0.37, 3.82)	NS
Ever self-injurious behaviour	0	118 (63.4)	40 (33.9)	1 (reference)	65 (55.1)	1 (reference)	13 (11.0)	1 (reference)
	1	34 (18.3)	12 (35.3)	1.04 (0.49, 2.20)	NS	17 (50.0)	0.91 (0.47, 1.75)	NS	5 (14.7)	1.33 (0.44, 4.01)	NS
	2	34 (18.3)	11 (32.4)	0.95(0.44, 2.06)	NS	19 (55.9)	1.01 (0.54, 1.92)	NS	4 (11.8)	1.07 (0.33, 3.49)	NS
Current faints, fits or blackouts	0	168 (90.3)	57 (33.9)	1 (reference)	93 (55.4)	1 (reference)	18 (10.7)	1 (reference)
	1	5 (2.2)	2 (40.0)	1.18 (0.22, 6.24)	NS	2 (40.0)	0.72 (0.14, 3.80)	NS	1 (20.0)	1.87 (0.21, 16.87)	NS
	2	13 (7.5)	4 (30.8)	0.91 (0.28, 2.89)	NS	6 (46.2)	0.83 (0.31, 2.27)	NS	3 (23.1)	2.15 (0.56, 8.28)	NS
Ever faints, fits or blackouts	0	160 (86.0)	55 (34.4)	1 (reference)	88 (55.0)	1 (reference)	17 (10.6)	1 (reference)
	1	8 (4.3)	2 (25.0)	0.73 (0.15, 3.53)	NS	4 (50.0)	0.91 (0.27, 3.10)	NS	2 (25.0)	2.35 (0.46, 11.99)	NS
	2	18 (9.7)	6 (33.3)	0.97 (0.37, 2.57)	NS	9 (50.0)	0.91 (0.39, 2.11)	NS	3 (16.7)	1.57 (0.42, 5.87)	NS
Current rocking	0	140 (75.3)	47 (33.6)	1 (reference)	77 (55.0)	1 (reference)	16 (11.4)	1 (reference)
	1	30 (16.1)	11 (36.7)	1.09 (0.51, 2.35)	NS	15 (50.0)	0.91 (0.46, 1.79)	NS	4 (13.3)	1.17 (0.36, 3.74)	NS
	2	16 (8.6)	5 (31.3)	0.93 (0.32, 2.68)	NS	9 (56.3)	1.02 (0.43, 2.42)	NS	2 (12.5)	1.09 (0.23, 5.20)	NS
Ever rocking	0	130 (69.9)	44 (33.8)	1 (reference)	71 (54.6)	1 (reference)	15 (11.5)	1 (reference)
	1	21 (11.3)	6 (28.6)	0.84 (0.32, 2.23)	NS	13 (61.9)	1.13 (0.54, 2.40)	NS	2 (9.5)	0.83 (0.18, 3.87)	NS
	2	35 (18.8)	13 (37.1)	1.10 (0.53, 2.26)	NS	17 (48.6)	0.89 (0.47, 1.70)	NS	5 (14.3)	1.24 (0.42, 3.64)	NS
Current overactivity	0	98 (52.7)	34 (34.7)	1 (reference)	46 (46.9)	1 (reference)	18 (18.4)	1 (reference)
	1	53 (28.5)	20 (37.7)	1.09 (0.57, 2.07)	NS	31 (58.5)	1.25 (0.71, 2.19)	NS	2 (3.8)	0.21 (0.05, 0.92)	0.04
	2	35 (18.8)	9 (25.7)	0.74 (0.32, 1.70)	NS	24 (68.6)	1.46 (0.78, 2.73)	NS	2 (5.7)	0.31 (0.07, 1.41)	NS
Ever overactivity	0	71 (38.2)	24 (33.8)	1 (reference)	32 (45.1)	1 (reference)	15 (21.1)	1 (reference)
	1	50 (26.9)	14 (28.0)	0.83 (0.39, 1.76)	NS	34 (68.0)	1.51 (0.83, 2.76)	NS	2 (4.0)	0.19 (0.04, 0.87)	0.03
	2	65 (34.9)	25 (38.5)	1.14 (0.59, 2.19)	NS	35 (53.8)	1.19 (0.66, 2.25)	NS	5 (7.7)	0.36 (0.13, 1.06)	NS

χ²-test was used to compare frequencies of genotypes between patients with different ADR-I item scores.

Met, methionine; Val, valine; OR, odds ratio; CI, confidence interval; NS, no statistically significant difference (P ≥ 0.05).

Table 4.

Analysis of the genotype frequency of the catechol-O-methyltransferase Val158Met polymorphism in Chinese Han children diagnosed with autism spectrum disorders (ASD), stratified according to ASD subtype.

ASD subtype	n	Met158/Met158		Val158/Met158		Val158/Val158
ASD subtype	n	n (%)	OR (95% CI)	n (%)	OR (95% CI)	n (%)	OR (95% CI)
ASD	186	63 (33.9)	1 (reference)	101 (54.3)	1 (reference)	22 (11.8)	1 (reference)
Autism	90	31 (34.4)	1.02 (0.62, 1.67)	48 (53.3)	0.98 (0.64,1.50)	11 (12.2)	1.03 (0.48, 2.22)
Asperger’s syndrome	54	18 (33.3)	0.98 (0.54, 1.80)	30 (55.6)	1.02 (0.62, 1.70)	6 (11.1)	0.94 (0.36, 2.43)
PDD-NOS	42	14 (33.3)	0.98 (0.50, 1.92)	23 (54.8)	1.01 (0.57, 1.77)	5 (11.9)	1.01 (0.36, 2.81)

No statistically significant between-group differences (P ≥ 0.05); χ²-test.

Met, methionine; Val, valine; OR, odds ratio; CI, confidence interval; PDD-NOS, pervasive developmental disorder-not otherwise specified.

Discussion

To our knowledge, this is the first report to evaluate the effect of the COMT gene Val158Met polymorphism on ASD risk in a Chinese Han population of children. This current study found that the frequency of the COMT gene Val158/Val158 genotype in children with ASD was significantly lower than that observed in healthy control subjects. When stratifying the children with ASD by select-item scores on the ADI-R, it was found that children with ‘current overactivity’ and ‘ever overactivity’ had a significantly lower frequency of the COMT gene Val158/Val158 genotype than those without this behaviour.

Research investigating associations between genetic polymorphisms and ASD risk is being reported with increasing frequency.¹³ For example, our previous study suggested that the methylenetetrahydrofolate reductase gene C677T polymorphism was a risk factor of ASD in Chinese Han children.¹⁴ The study by Guerini et al.¹⁵ showed that synaptosomal-associated protein of 25 kDa gene single nucleotide polymorphisms (SNPs) were associated with hyperactivity in ASD. A case–control and family-based replication study demonstrated that variants of the hepatocyte growth-factor receptor gene may be relevant to ASD susceptibility in the Chinese Han population.¹⁶ Results of a family-based linkage study found that human leucocyte antigen gene polymorphisms were associated with ASD in Italian children.¹⁷ A case–control study of 235 patients with ASD and 214 controls found a significant association between variants of the NADH-ubiquinone oxidoreductase 1 alpha subcomplex 5 gene and ASD in a Japanese population.¹⁸ Gebril et al.¹⁹ reported on the first pilot study of the possible genetic association between ASD and haemochromatosis gene polymorphisms among Egyptians. A family-based association study in an exploratory sample of 277 ASD genetic resource-exchange families and in a replication sample (including 406 families primarily recruited in Italy) provided converging evidence for an association between variants in the ATPase Ca²⁺ transporting plasma membrane 2 gene and ASD in male subjects.²⁰ A family-based association test (FBAT) in 151 Korean trios demonstrated a statistically significant association between ASD and SNPs in the promoter region of the arginine vasopressin receptor 1A gene.²¹ A case–control and family-based study demonstrated that a strong and consistent association was observed between two SNPs within the paired-like homeodomain transcription factor 1 gene and ASD.²² The results of a FBAT suggested that the contactin associated protein-like 2 gene was a susceptibility gene for ASD in the Chinese Han population.²³ A family-based association analysis suggested a potential association between the glutamate receptor, ionotropic, kainate 2 gene and ASD in the Korean population.²⁴ Polymorphisms in leucine-rich repeat genes were associated with ASD susceptibility in populations of European ancestry.²⁵ A population-based case–control study showed significant associations between the rs3918346 and rs3825251 SNPs of the D-amino-acid oxidase gene and boys with ASD.²⁶

The COMT gene Val158Met polymorphism has been shown to be associated with many other diseases. For example, a meta-analysis of 15 studies (comprising 2370 individuals) found that male patients with schizophrenia who carried the low-activity Met158 allele in the COMT gene were at a modestly elevated risk of violence.⁷ The COMT gene 158Met allele modulates neural substrates of negative versus positive emotional processing.²⁷ A meta-analysis of 19 studies demonstrated that the low-activity Met158 allele in the COMT gene conferred risk for bipolar disorder.²⁸ The COMT gene Val158Met polymorphism modulates the association of serious life events and impulsive aggression in female patients with borderline personality disorder.²⁹ A meta-analysis of 12 studies demonstrated that there was a small but significant relationship between the COMT gene Val158Met genotype and executive function in healthy individuals.³⁰ The COMT gene Val158 allele might be related to poor performance on detecting interpersonal problems, and attention in schizophrenia.^31–33 A systematic review and meta-analysis showed that the COMT gene Met158 allele was a risk allele for chronic human pain.³⁴ A case–control study suggested that the COMT gene Val158 allele was associated with a lower risk of osteoporotic fracture in a Chinese population, especially for risk of vertebral fracture.³⁵ A meta-analysis of 30,199 cases and 38,922 controls indicated that the COMT gene Val158Met polymorphism may be associated with decreased breast cancer risk in a Caucasian population.³⁶

Our current study had a number of limitations. First, these results should be interpreted with caution because the population was only from China, which reduces the possibility of confounding because of ethnicity, but does not permit extrapolation of the results to other ethnic groups. Secondly, the sample size was relatively small, so the statistical power of the study remains very limited. Thirdly, this was a population-based, case–control study, so selection bias may have been unavoidable and the subjects may not be representative of the general population.

In conclusion, the findings from this current study suggest that the COMT gene Val158Met polymorphism may be a biomarker for phenotypic variation in ASD, but these preliminary findings remain tentative pending replication in larger, independent populations.

Footnotes

Declaration of conflicting interest

The authors declare that there are no conflicts of interest.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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