en علوم پایه پزشکی Basic Medical Sciences تحقیقی Original article <div style="text-align: justify;"><span style="font-size:12px;"><span style="font-family:Times New Roman;"><b>Background:</b> The second-to-fourth digit ratio (2D:4D), obtained by dividing the length of the index finger by that of the ring finger, varies significantly by sex, race, and ethnicity. This ratio has previously been associated with both autism spectrum disorder and Down syndrome. The current study, therefore, examined the 2D:4D digit ratio in individuals with these two neurodevelopmental conditions recruited from special needs schools in Port Harcourt, Rivers State, Nigeria.<br> <b>Methods:</b> This cross-sectional descriptive study involved 200 participants: 100 with Down syndrome and 100 with autism. Participants met specific inclusion criteria, including the absence of hand deformities and a confirmed diagnosis. The lengths of the 2nd and 4th digits were measured with a digital vernier calliper. SPSS software, version 19, was used for data analysis.<br> <b>Results:</b> Male autistic subjects showed a normal right-hand digit ratio (0.98 &plusmn; 0.12) but an elevated left-hand ratio (1.00 &plusmn; 0.01), whereas female autistic subjects displayed normal ratios bilaterally (1.00 &plusmn; 0.01 left; 1.00 &plusmn; 0.00 right). Males with Down syndrome exhibited higher-than-normal ratios on both hands (Left: 1.02 &plusmn; 0.03; right: 1.01 &plusmn; 0.01), and females showed ratios of 1.01 &plusmn; 0.01 (Left) and 1.00 &plusmn; 0.00 (Right). Mean comparisons revealed significant differences (P-Value < 0.05) between autistic and Down syndrome subjects of both sexes, with individuals with Down syndrome consistently demonstrating higher digit ratios than autistic individuals.<br> <b>Conclusion</b>: Subjects with Down syndrome had significantly higher digit ratios than autistic subjects. This finding confirms that digit ratios are sexually dimorphic and suggests hypermasculinity in autistic males because of their lower digit ratios.</span></span></div> Digit Ratios, Autism (Autistic Disorder), Down Syndrome, (The second-to-fourth digit ratio) 2D:4D 0 0 http://goums.ac.ir/jorjanijournal/browse.php?a_code=A-10-989-1&slc_lang=en&sid=1 Gwunireama Israel Ukie israel.gwunireama@uniport.edu.ng 100319475328460010867 0009-0007-0049-5030 Yes Department of Anatomy, Faculty of Basic Medical Sciences, University of Port Harcourt, Port Harcourt, Nigeria Momodu Fawziyah Osinhe fabzmomodu@gmail.com 100319475328460010868 100319475328460010868 No Department of Anatomy, Faculty of Basic Medical Sciences, University of Port Harcourt, Port Harcourt, Nigeria