Table 3.
Causes of mental retardation identified in 595 institutionalized patients
| Diagnosis | Number | Per cent |
|---|---|---|
| Diagnosis not made | 253 | 42·5 |
| Genetic disorders: | ||
| Autosomal dominant: | ||
| tuberous sclerosis | 7 | 1·2 |
| Autosomal recessive: | ||
| primary microcephaly | 3 | 0·5 |
| consanguinity (e.g. first cousins) | 2 | 0·3 |
| phenylketonuria | 7 | 1·2 |
| sudanophilic leukodystrophy of Pelizaeus-Merzbacher type | 2 | 0·3 |
| familial mental retardation★ | 1 | 0·2 |
| X-linked recessive: | ||
| familial mental retardation† | 3 | 0·5 |
| Chromosome: | ||
| Down syndrome | 31 | 5·2 |
| ring chromosome 22 syndrome | 1 | 0·2 |
| fragile-X syndrome‡ | 4 | 0·7 |
| 46,XX,12p- | 1 | 0·2 |
| cri-du-chat syndrome | 1 | 0·2 |
| unspecified chromosome abnormality | 1 | 0·2 |
| Other genetic/multifactorial: | ||
| mental retardation§ | 64 | 10·8 |
| Environment: | ||
| Trauma: | ||
| birth trauma/anoxia | 52 | 8·7 |
| Postnatal injury: | ||
| hyperthermia | 2 | 0·3 |
| post polio immunization reaction | 1 | 0·2 |
| post immunization reaction | 1 | 0·2 |
| head trauma | 1 | 0·2 |
| hypoxia | 4 | 0·7 |
| injury (unspecified) | 11 | 1·8 |
| Drugs: | ||
| fetal alcohol syndrome | 2 | 0·3 |
| fetal dilantin syndrome | 1 | 0·2 |
| intoxication, toxaemia of pregnancy | 3 | 0·5 |
| Prematurity: | ||
| <28 weeks gestation | 15 | 2·5 |
| 29–37 weeks gestation | 27 | 4·5 |
| Infection: | ||
| Viral: | ||
| postnatal cerebral — unspecified | 4 | 0·6 |
| TORCHS — unspecified | 2 | 0·3 |
| congenital rubella | 7 | 1·2 |
| congenital syphilis | 2 | 0·3 |
| cytomegalic inclusion disease | 4 | 0·7 |
| Bacterial: | ||
| postnatal cerebral — unspecified | 18 | 3·0 |
| Unspecified type: | ||
| postnatal cerebral — unspecified | 13 | 2·2 |
| Birth defects: | ||
| malformation: | ||
| congenital hydrocephaly | 1 | 0·2 |
| hydranencephaly | 1 | 0·2 |
| MR/MCA — unspecified | 6 | 1·0 |
| craniostenosis | 2 | 0·3 |
| meningomyelocele | 4 | 0·7 |
| other cerebral malformations | 2 | 0·3 |
| other craniofacial anomalies | 1 | 0·2 |
| Diagnosis made but cause unknown: | ||
| communicating hydrocephaly | 1 | 0·2 |
| infantile autism | 3 | 0·5 |
| Rubinstein-Taybi syndrome | 1 | 0·2 |
| Smith-Lemli-Opitz syndrome | 1 | 0·2 |
| microcephaly | 3 | 0·5 |
| neuromuscular disorder (unspecified type) | 1 | 0·2 |
| Proteus syndrome | 1 | 0·2 |
| Cornelia de Lange syndrome | 5 | 0·8 |
| cutis verticis gyrata | 1 | 0·2 |
| hyperbilirubinemia intoxication | 4 | 0·7 |
| macrocephalus | 1 | 0·2 |
| congenital thyroid dysfunction | 2 | 0·3 |
| other endocrine disorder (not thyroid) | 1 | 0·2 |
| other fibre tracts or neural groups, degenerative | 1 | 0·2 |
| tumors — unspecified type or location | 1 | 0·2 |
| Total | 595 | 100 |
★
Mental retardation in siblings with similar clinical findings and degree of retardation.
†
Mental retardation in first- or second-degree relatives exhibiting an X-linked pattern of inheritance.
‡
Only males without a cause of their mental retardation (n=201) were screened for the fragile-X syndrome.
§
Mental retardation found in first or second degree relatives but with no recognizable pattern of inheritance.