Intellectual Disability

Introduction

Definition

• Statistically, an intellectual disability is defined by an IQ score of > 2 SDs below the population mean (M = 100, SD = 15) and adaptive skill impairment.
• Adaptive skill impairment is as important as a low IQ and means the child does not meet normal/age-appropriate skills in areas such as communication, self-care, academics, and social interactions.

Classification

Epidemiology

• Mild intellectual disabilities occur at a rate of 20-30/1,000.
• These disabilities are often hereditary, are more common in boys, and occur more frequently in lower socioeconomic groups.
• Only 4-8% of children with mild intellectual disabilities have identifiable chromosomal abnormalities.
• Severe intellectual disabilities are also less prevalent, but more common in boys, and are not associated with socioeconomic factors.

Etiology

• The most common form in intellectual disability is: mild, no associated CNS disorder, and mostly due to psychological disturbances.
• Up to 40-45% of severe intellectual disability is due to chromosomal abnormalities and genetic disorders (trisomies, fragile X syndrome,Prader-Willi and Angelman syndromes).
• 20-25% of severe intellectual disability is due to central nervous system injury (teratogens, such as maternal alcohol; infection; perinatal and postnatal insults; developmental anomalies).
• Additional causes include: inborn errors of metabolism and other endocrine/metabolic etiologies (e.g cretinism)

Diagnosis

• Screening for developmental abnormalities must be performed at all well-child visits and whenever a parent raises concern.
• The goal is early diagnosis with referral to the appropriate intervention services.
• Diagnostic testing for children with intellectual disabilities can include neuroimaging, metabolic screening (including thyroid), and cytogenetic chromosomal analysis.
• Electroencephalography is sometimes also indicated.
• Metabolic screening is not recommended in children with idiopathic intellectual disabilities who are otherwise asymptomatic.
• Cytogenetic chromosome testing is recommended if one of the following is present: Microcephaly, Dysmorphic features, Family history of intellectual disability, Family history of fetal loss, IQ < 50, Skin pigment abnormalities, Suspected genetic syndrome.

Treatment

• Treat underlying cause ( hypothyroidism, neonatal jaundice, hypoglycemia).
• Rehabilitation according to the degree of Intellectual disability.