Table 1.
Characteristics of studies evaluating 2D:4D in neurodevelopmental disorders, i.e., attention deficit-hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and intellectual disability (ID)
| Diagnosis (tool) | First author | Year | Country | Patients | Controls | Hand | 2D:4D measurement tool | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
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| Number | Mean age (range) | Male, n (%) | Number | Mean age (range) | Male, n (%) | |||||||
| ADHD (DSM-IV) | Buru | 2017 | Turkey | 104 | / (7−17) | 77 (74.03) | 436 | / (7−17) | 240 (55.04) | L, R | Digital compass (direct) | |
| ADHD (DSM-IV-TR) | Lemiere | 2010 | Belgium | 64 | / (7−12) | 47 (73.44) | 46 | / (7−12) | 25 (54.35) | / | Scanned photocopies (indirect) | |
| ADHD (Clinical) | Martel | 2009 | USA | 168 | 12.71 (8−17) | 106 (63.10) | 144 | 14.01 (8−17) | 72 (50) | R | Ruler (direct) | |
| ADHD (DSM-IV-TR) | McFadden | 2005 | USA | 46 | 9.83 (7−15) | 34 (73.91) | 33 | 10.6 (7−15) | 17 (51.51) | L, R | Photocopy or digital scanner (indirect) | |
| ASD (DSM-IV) | Al-Zaid | 2015 | Saudi Arabia | 31 | 5.59 (3−8) | 31 (100) | 29 | 5.59 (3−8) | 29 (100) | R | Digital Caliper (direct) | |
| ASD (DSM-IV-TR, ADOS) | Baharara | 2014 | Iran | 48 | 7.38 (7−8) | 38 (79.17) | 41 | 7.46 (7−8) | 31 (75.61) | L, R | Ruler (direct) | |
| ASD (Clinical, ADOS) | Bejerot | 2012 | Sweden | 50 | 30 (20−47) | 26 (52) | 53 | 30.3 (20−47) | 28 (52.83) | L, R | Digital Caliper (direct) | |
| ASD (DSM-IV) | De Bruin | 2006 | The Netherlands | 24 | 9 (6−14) | 24 (100) | 96 | 9 (6−13) | 96 (100) | L, R | Digital Caliper (direct) | |
| ASD (DSM-IV-TR) | Falter | 2008 | UK | 28 | 12.7 (/) | 27 (96.43) | 28 | 12.7 (/) | 27 (96.43) | L, R | Digital Caliper (direct) | |
| ASD (ADI-R) | Hauth | 2014 | The Netherlands | 216 | 11.6 (4−21) | 178 (82.40) | 174 | 11 (4−21) | 79 (45.40) | L, R | Tape (indirect) | |
| ASD (DSM-IV) | Krajmer | 2011 | Slovak Republic | 56 | 11.2 (/) | 56 (100) | 32 | 12.1 (/) | 32 (100) | R | Scanner (indirect) | |
| ASD (DSM-IV-TR, ICD-10) | Lai | 2013 | UK | 60 | 27.5 (18−49) | 0 | 60 | 27.8 (18−49) | 0 | L, R | Digital Caliper (direct) | |
| ASD (DSM-5, DISCO) | Masuya | 2015 | Japan | 52 | 28.5 (/) | 35 (67.31) | 116 | 27.74 (/) | 59 (42.45) | L, R | Digital Caliper (direct) | |
| ASD (DSM-IV) | Milne | 2006 | UK | 23 | 10.8 (/) | 22 (95.65) | 23 | 10.8 (/) | 10 (43.48) | / | Digital Caliper (direct) | |
| ASD (ASQ) | Manning | 2001 | UK | 72 | / (2−15) | 62 (86.11) | 72 | / (2−15) | 62 (86.11) | Mean L, R | Digital Caliper (direct) | |
| ASD (DSM-IV) | Noipayak | 2009 | Thailand | 46 | 5.25 (1.5−15) | 39 (84.78) | 46 | 5.25 (1.5−15) | 39 (84.78) | L, R | Digital Caliper (direct) | |
| ASD (Clinical) | Rohde | 2018 | Germany | 26 | 42.86 (20−55) | 14 (53.84) | 26 | 41.44 (20−55) | 14 (53.85) | R | Ruler (direct) | |
| ASD (ADOS, ADI-R) | Schieve | 2018 | USA | 599 | / (2−5) | 487 (81.30) | 811 | / (2−5) | 431 (53.14) | L, R | Scanner (indirect) | |
| ASD (DSM-IV) | Sugie | 2010 | Japan | 98 | 12.7 (5−31) | 82 (85.71) | 89 | / | / | R | Digital Camera (indirect) | |
| ASD (DSM-IV-TR) | Togo | 2019 | Japan | 20 | 26.75 (/) | 20 (100) | 14 | 26 (/) | 14 (100) | L, R | Digital Photos (indirect) | |
| Intellectual disability (WISC-III) | Ypsilanti | 2008 | Greece | 100 | 17.4 (14−18) | 47 (47) | 85 | 19.24 (18−23) | 37 (43.53) | R | Digital Caliper (direct) | |
2D:4D, Second-to-fourth Digit Ratio ADI-R, Autism Diagnostic Interview-Revised; ADOS, Autism Diagnostic Observation Schedule; ASQ, Autism Screening Questionnaire; DSM, Diagnostic and Statistical Manual of Mental Disorders; L, left; R, right; WISC-III, Wechsler Intelligence Scale for Children-Third Edition; ICD, International Classification of Diseases; DISCO, Diagnostic Interview for Social and Communication Disorders; /, not available.