Neurodevelopmental and Genetic Disorders
Intellectual disability and autism
Intellectual disability requires deficits in intellectual function and adaptive behavior, with onset during development; severity is based on adaptive functioning, not IQ alone. Autism spectrum disorder requires persistent social communication deficits plus restricted, repetitive behaviors or interests, with early onset. Language delay alone is not autism.
Cerebral palsy
Cerebral palsy is a nonprogressive motor disorder causing activity limitation, often with abnormal tone, persistence of primitive reflexes, and asymmetry. Neuroimaging may identify periventricular leukomalacia or malformation.
Genetic syndromes
Down syndrome features hypotonia, upslanting palpebral fissures, and a single palmar crease; monitor for congenital heart disease, thyroid disease, hearing loss, sleep apnea, and atlantoaxial instability. Fragile X syndrome is caused by FMR1 expansion; boys show intellectual disability, long face, large ears, and macroorchidism after puberty. Rett syndrome (MECP2) affects girls with regression and hand-wringing. Tuberous sclerosis causes ash-leaf spots, seizures, and tumors. Duchenne muscular dystrophy causes proximal weakness, Gowers sign, and elevated CK. Neurofibromatosis type 1 causes café-au-lait spots, freckling, and optic glioma.
Traps
Do not diagnose autism from language delay alone. Do not miss hearing loss. Do not attribute regression to autism without considering Rett, epilepsy, or metabolic disease. Remember that Down syndrome health supervision differs from routine care.
Worked example
A 6-year-old boy has intellectual disability, a long face, large ears, and a maternal uncle with learning problems. Fragile X DNA testing is indicated. The rule of thumb: when intellectual disability or autism is accompanied by dysmorphic features or a family history, offer genetic evaluation.