Cause of ID as determined in the IDEA database for children who survived to 1 year of age and were either identified/not identified with ID through HMDS codes
| Cause of ID | In IDEA and identified with ID in HMDS | In IDEA and not identified with ID in HMDS | Total | ||
| n | % | n | % | n | |
| Prenatal conditions | |||||
| Genetic or chromosomal | |||||
| Down syndrome | 589 | 94.2 | 36 | 5.8 | 625 |
| Tuberous sclerosis | 29 | 90.6 | 3 | 9.4 | 32 |
| Prader-Willi syndrome | 20 | 87.0 | 3 | 13.0 | 23 |
| Neurofibromatosis | 12 | 70.6 | 5 | 29.4 | 17 |
| Muscular dystrophy | 4 | 57.1 | 3 | 42.9 | 7 |
| Fragile X | 16 | 51.6 | 15 | 48.4 | 31 |
| Other chromosomal | 59 | 45.0 | 72 | 55.0 | 131 |
| X linked inheritance | 4 | 36.4 | 7 | 63.6 | 11 |
| Metabolic (possible) | 9 | 29.0 | 22 | 71.0 | 31 |
| Myotonic dystrophy | 3 | 27.3 | 8 | 72.7 | 11 |
| Syndrome grouped | 45 | 26.5 | 125 | 73.5 | 170 |
| Mucopolysaccharidosis | 1 | 25.0 | 3 | 75.0 | 4 |
| Autosomal | 21 | 23.9 | 67 | 76.1 | 88 |
| Prenatal aetiology | 8 | 18.2 | 36 | 81.8 | 44 |
| Williams syndrome | 5 | 16.1 | 26 | 83.9 | 31 |
| Neurodegenerative disorders | 1 | 11.1 | 8 | 88.9 | 9 |
| Sex chromosome | 2 | 9.5 | 19 | 90.5 | 21 |
| Mitochondria | 1 | 7.7 | 12 | 92.3 | 13 |
| Metabolic | 1 | 5.9 | 16 | 94.1 | 17 |
| Teratogenic | |||||
| Congenital cytomegalic inclusion | 12 | 50.0 | 12 | 50.0 | 24 |
| Other potential teratogens | 4 | 16.7 | 20 | 83.3 | 24 |
| Other prenatal infections | 1 | 9.1 | 10 | 90.9 | 11 |
| Potential foetal alcohol syndrome | 7 | 8.0 | 81 | 92.1 | 88 |
| CNS and other birth defects | |||||
| Unspecified neurological | 32 | 42.7 | 43 | 57.3 | 75 |
| Congenital hypothyroidism | 1 | 25.0 | 3 | 75.0 | 4 |
| Spina bifida meningocoele | 3 | 25.0 | 9 | 75.0 | 12 |
| Unknown prenatal | 51 | 22.6 | 175 | 77.4 | 226 |
| Microcephaly | 7 | 17.5 | 33 | 82.5 | 40 |
| CNS: malformations of gyri | 4 | 17.4 | 19 | 82.6 | 23 |
| Hydrocephalus | 4 | 16.7 | 20 | 83.3 | 24 |
| Macrocephaly | 3 | 16.7 | 15 | 83.3 | 18 |
| Cranial anomalies | 6 | 16.2 | 31 | 83.8 | 37 |
| CNS malformations | 6 | 10.2 | 53 | 89.8 | 59 |
| Perinatal conditions | |||||
| Hypoxic–ischaemic encephalopathy | 27 | 29.0 | 66 | 71.0 | 93 |
| Perinatal: neonatal | 2 | 28.6 | 5 | 71.4 | 7 |
| Postneonatal conditions | |||||
| Postnatal asphyxia | 13 | 44.8 | 16 | 55.2 | 29 |
| Postnatal injury | 23 | 31.5 | 50 | 68.5 | 73 |
| Postneonatal infection | 21 | 29.6 | 50 | 70.4 | 71 |
| Intracranial neoplasm | 2 | 28.6 | 5 | 71.4 | 7 |
| No defined cause | |||||
| Associated with epilepsy | 44 | 24.2 | 138 | 75.8 | 182 |
| Cultural familial IH | 29 | 20.4 | 113 | 79.6 | 142 |
| Associated with coexisting disability | 2 | 20.0 | 8 | 80.0 | 10 |
| Associated with psychotic disorder | 4 | 14.3 | 24 | 85.7 | 28 |
| Associated maternal medical condition | 4 | 10.0 | 36 | 90.0 | 40 |
| No defined cause (functional reaction alone) | 66 | 8.7 | 689 | 91.3 | 755 |
| Other developmental disorders | 3 | 8.3 | 33 | 91.7 | 36 |
| Familial unspecified | 20 | 6.3 | 300 | 93.8 | 320 |
| Associated with psychosocial factors | 2 | 6.3 | 30 | 93.8 | 32 |
| Prematurity | 9 | 6.3 | 133 | 93.7 | 142 |
| Multiple birth | 2 | 5.0 | 38 | 95.0 | 40 |
| Asperger’s | 1 | 3.9 | 25 | 96.2 | 26 |
| Autism | 42 | 3.0 | 1342 | 97.0 | 1384 |
| Intrauterine growth restriction | 1 | 2.9 | 34 | 97.1 | 35 |
| Unassessed | 114 | 2.7 | 4103 | 97.3 | 4217 |
| Total | 1412 | 14.6 | 8292 | 85.4 | 9704 |
CNS, central nervous system; HMDS, Hospital Morbidity Data System; ID, intellectual disability; IDEA, Intellectual Disability Exploring Answers; IH, Intellectual handicap.