Intellectual disability may be either generalized (cognitive impairment) or specific to one area (learning difficulty). Children with cognitive impairment have below-average IQ, at <70. The degree of cognitive impairment depends on the underlying disorder and its severity. An IQ of 50 to 70 is classed as mild cognitive impairment. Children with a specific learning difficulty, on the other hand, have difficulties with particular mental tasks but a normal IQ. Examples include difficulties with speech (specific language impairment), reading and writing (dyslexia), and use of numbers (dyscalculia). Although the terms "learning difficulty" and "cognitive impairment" have specific definitions, they are sometimes used interchangeably by clinicians.
Cognitive impairment affects 2-3% of children. Down syndrome and fetal alcohol syndrome are among the most common identified causes of cognitive impairment. The prevalence of learning difficulties is more difficult to determine because of the spectrum of disabilities and the variation in diagnostic criteria. Most estimates suggest that the lifetime prevalence of learning disability is about 10%; males are more likely to be affected than females. Dyslexia is the most common specific learning disability (affecting about 5% to 12% of children).
The majority of conditions associated with both specific learning difficulties and generalized cognitive impairment are developmental in origin, are linked to abnormalities in brain structure and function, and are present from birth. Learning difficulty or cognitive impairment may be part of a syndrome, and there may be a family history of similar difficulties. Generalized cognitive impairment is often associated with a history of delayed developmental milestones; the age at which it becomes manifest varies according to its severity. In some children, mild generalized cognitive impairment becomes more obvious when the child starts attending school.
The English Learning Disabilities Mortality Review (LeDeR) program in 2018 found that the median age at death for 3860 people with learning disabilities (ages 4 years and over) was 60 years for males and 59 years for females.
Multidisciplinary team approach
Children who develop new specific learning difficulties or who have recently been identified as having cognitive impairment should be referred to a pediatric neurologist. An acquired disability due to intracranial pathology must be considered if there is an acute onset or a regression of previously acquired skills. However, often the specific learning difficulties or cognitive impairment may have been present for some time but only recently noted (e.g., on starting school).
A multidisciplinary team (MDT) assessment is desirable for accurate diagnosis and advice regarding appropriate interventions and educational placement. An MDT assessment includes the pediatrician or child psychiatrist and allied professionals such as a psychologist and a speech therapist. Children with motor coordination difficulties (developmental coordination disorder, or dyspraxia) resulting in physical problems with writing may benefit from assessment by an occupational therapist. The role of the clinical psychologist is to identify the child's cognitive ability (IQ, or age-equivalent developmental level, which can be compared with their chronologic age). Speech therapists help assess the child's expressive and receptive (understanding) language abilities and compare these with the overall level of cognitive ability. Some children have a discrepancy between cognitive and language abilities. For example, children with autism sometimes have relatively superior nonverbal skills compared with verbal performance. There is evidence that early reading interventions may be particularly helpful in improving expressive and receptive language as well as reading in children with intellectual disability.
"Cerebral palsy" is a diagnosis given to children with a static brain injury of varying etiology (e.g., preterm birth, hypoxic-ischemic injury, meningitis, or intracerebral hemorrhage), associated with a disorder of movement and posture. Cerebral palsy is not a cause of cognitive impairment. However, the two conditions can coexist, and for this reason a cause and effect relationship is often mistakenly assumed both by clinicians and by the general public.
- Attention deficit hyperactivity disorder (ADHD)
- Down syndrome (trisomy 21)
- Fragile X syndrome
- Tuberous sclerosis
- Autism spectrum disorder
- Fetal alcohol syndrome
- Absence epilepsy
- Social (pragmatic) communication disorder
- Specific language disorder
- Central auditory processing disorder (CAPD)
- Developmental coordination disorder/dyspraxia
- Prader-Willi syndrome
- Angelman syndrome
- William syndrome
- Rett syndrome
- DiGeorge syndrome (velocardiofacial syndrome)
- Turner syndrome
- Congenital cytomegalovirus
- Congenital toxoplasmosis
- Congenital rubella
- Teratogenic drugs
- Extreme preterm birth
- Perinatal hypoxia
- Bacterial meningitis
- Brain tumor
- Traumatic brain injury
- Congenital hypothyroidism
- Inborn errors of metabolism
- Psychosocial deprivation
- Acquired epileptic aphasia (Landau-Kleffner syndrome)
- Epileptic encephalopathies
- 15q11 duplication syndromes
- 16p11.2 deletion syndrome
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