Mental Retardation and how to evaluate normal IQ

Definition

•            A group of disorders that have in common deficits of adaptive and intellectual function and an age of onset before maturity is reached.

•          Intelligence: is a multifactorial mental process of abstract of thinking, visual, auditory, memory, verbal expression and manipulative capacities.

•          Intelligence is usually expressed in terms of intelligence quotient (IQ).

IQ = Mental age´ 100                                   Normal IQ = 90 - 110

        Chronologic age

Prevalence of mental retardation is 3%.

Etiological classification

I- Prenatal causes

1- Genetic

  a- Chromosomal abnormalities (Down  syndrome).

  b- Metabolic disorders (e.g. phenylketonuria, and galactosemia).

  c- Cerebral degeneration disorders (e.g.mucopolysaccharidosis).

  d- Structural disorders (e.g. genetic microcephaly, hydrocephalus).

2- Intrauterine

  a- Congenital infections e.g. rubella, toxoplasmosis.       

  b- Drugs and toxins e.g. phenytoin, alcohol, tobaco.

  c- Radiation.

  d- Placental insufficiency. -

II- Perinatal

  1- During pregnancy: antepartum hemorrhage, toxemia.

  2- During labour: asphyxia,trauma, intracranial hemorrhage.    

III- Neonatal: intracranial hemorrhage, intracranial infections, hypoglycemia, kernicterus.

IV- Postneonatal

  1- Trauma: e.g. intracranial hemorrhage.        

  2- Infections: e.g. encephalitis, meningitis.

  3- Anoxia: e.g. asphyxia, status epilepticus.  

  4- Metabolic: e.g. hypoglycemia.

  5- Endocrine: e.g. hypothyroidism.

  6- Poisoning: e.g. lead, copper.

Clinical picture

In infancy

In early childhood

In late childhood

Diagnosis

· Delayed developmental milestones suggest the diagnosis.

· Detailed history

· Investigations should be directed according to the clinical possibilities (skull x-ray, CT scan, fundus examination, karyotyping, serological investigations).

· Screening tests are indicated to detect early the preventable/curable conditions e.g. T3 and T4 (hypothyroidism), urine reducing substance (galactosemia) and urine ferric chloride test (phenylketonuria).

Prevention of mental retardation     

1- Prevention of delivery of retarded children:

a- Vaccination of all females against rubella before child bearing period.

b- In untreatable inherited disorders, avoid further pregnancies, especially when the recurrence risk is high.

c- Avoidance of conditions that may lead to acquired retardation during intrauterine, perinatal 

and postnatal periods.

2- Early diagnosis and treatment of preventable/treatable conditions, e.g. congenital hypothyroidism, galactosemia and phenylketonuria by suitable screening tests.

Management of mental retardation

1- In treatable conditions, the specific therapy will prevent further impairment of mental abilities. Congenital hypothyroidism requires life long therapy with thyroid hormone. Galactosemia requires elimination of galactose from the diet and using galactose-free diet. Phenylketonuria requires elimination of phenylalanine and using phenylalanine-free milk and diet.

2- In untreatable conditions management is supportive:

  a- Treatment of associated problems e.g. epilepsy or hearing defect.

  b- Education and training according to the degree of mental retardation.

  c- Emotional support to the family.

  d- Institutionalization for the profoundly retarded children.