A diagnosis of MR/intellectual disability should be made only through a psychodiagnostic assessment conducted by a mental health provider who is trained and licensed to conduct formal psychological testing.

• 3-generation family history
• Children with profound or severe MR typically are diagnosed at birth or during the newborn period and are more likely to have dysmorphic features.
• Children with MR often are identified because they fail to meet motor or language milestones.

Careful examination by a physician trained in the assessment of morphologic features suggestive of a specific etiology for MR (e.g., microcephaly) (4)

• Visual and hearing tests to rule out these etiologies as a cause of impairment and provide an assessment of visual and auditory functioning, which often are impaired in children and adults with MR
• Formal testing of intellectual and adaptive functioning:
  • A child's communication skills must be considered in test selection. For example, a patient with auditory processing issues or limited expressive or receptive language skills may need to be assessed using a nonverbal IQ test, such as the Leiter-R, Test of Nonverbal Intelligence, or other nonverbal measures.
  • Commonly used intelligence tests (e.g., Bayley Scales of Infant Development, Stanford-Binet Intelligence Scale, Wechsler Intelligence Scales) are determined by age/developmental level of the child.
  • Common tests of adaptive functioning include the Vineland Adaptive Behavior Scales, 2nd edition, and Adaptive Behavior Assessment System, 2nd ed. These tests assess areas of functioning, such as age-appropriate communication, social skills, activities of daily living, and motor skills.

Lab

• Metabolic screening is not routine unless evidence in history and physical or no newborn screening records (5)[B]
• Lead as per current targeted guidelines (5)[B]
• Thyroid-stimulating hormone if systemic features present or no newborn screening (5)[B]
• Routine cytogenetic testing (karyotype) (5)[B]:
  • Fragile X screening (FMR1 gene), particularly if there is family history of intellectual disability (5)[B]
  • Rett syndrome (MECP2 gene) in women with unexplained moderate-to-severe intellectual disability (5)[B]
• Molecular screening such as array comparative genomic hybridization is used increasingly and may yield a diagnosis in 10% undiagnosed cases (4)[B].

Imaging

• Neuroimaging (MRI more sensitive than CT) is routinely recommended. The presence of physical findings (microcephaly, focal motor deficit) will increase the yield of a specific diagnosis (5)[B].
• MRI may show mild cerebral abnormalities but is unlikely to establish etiology of MR (4).

Follow-Up and Special Considerations Electroencephalogram is not routine unless epilepsy or a specific epileptiform syndrome is present (5)[C].

• Brain tumors
• Auditory, visual, and/or speech/language impairment
• Autistic disorder (language and social skills are more affected than other cognitive abilities); however, 75% of individuals with an autistic disorder may meet criteria for a comorbid diagnosis of MR.
• Expressive or receptive language disorders
• Cerebral palsy
• Emotional or behavioral disturbance
• Learning disorders (reading, math, written expression)
• Auditory or sensory processing difficulties
• Lack of environmental opportunities for appropriate development