2D:4D Ratio and Autism Spectrum Disorder in Brunei Darussalam

Despite the global increase in the prevalence of autism spectrum disorders (ASD), relevant research studies are lacking in Brunei Darussalam. Various studies have shown a significant association between a lowered 2D:4D ratio (ratio of second digit/index finger to the fourth digit/ring finger) and ASD, making it one of the potential phenotypic biomarkers for early detection of autism, which is important for early intervention and management.

The objective of this study is to explore the association between 2D:4D ratio and ASD in Brunei Darussalam, as a potential tool to complement early ASD diagnosis.

We conducted a case-control study comprising 28 ASD and 62 typically developing (TD) children in the case and control group, respectively (age range: 3-11 years old; median age: 6 years old). Median 2D:4D ratios were measured, compared and analysed between the two groups. Logistic regression models were used to explore potential associations between the median 2D:4D ratio and ASD in respective gender, for both left and right hands, independently.

Our study shows that the median 2D:4D ratio of left hand in ASD males is significantly lower than those in TD males, after adjusting for ethnicity and age [Odds Ratio (OR) = 0.57 (95% Confidence Interval (CI): 0.31-0.96); p = 0.044]. For females, there is no association of ASD with the median left hand 2D:4D ratio [OR = 3.09 (95% CI: 0.98-19.86); p = 0.144] or the median right hand 2D:4D ratio [OR = 1.23 (95% CI: 0.42-3.88); p = 0.702]. Our study also shows a significant positive correlation and/or a reduced asymmetry between the average 2D:4D ratio of left hands and right hands in ASD males (Pearson's correlation (r) = 0.48; 95% CI: 0.076-0.75, p = 0.023).

There is significant association between a lowered median 2D:4D ratio of the left hand (in males only) and ASD diagnosis. Once validated in a larger sample size, a lowered median 2D:4D ratio on the left hand may be a potential tool to complement ASD diagnosis for males in our study population. There is no association between the median 2D:4D ratio (left or right hands) and ASD in females, which could be due to the small female sample size and/or the possibility of different aetiology for ASD in females. Reduced asymmetry between the average 2D:4D ratio of left and right hands observed in ASD males only (not in ASD females) also suggests the importance of considering gender-specific biomarkers for ASD diagnosis.