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Key Features

  • Head circumference more than 2 standard deviations below the mean for age and sex

  • Nearly always associated with developmental delay and learning difficulties

  • Primary microcephaly is present at birth

  • Secondary microcephaly develops postnatally

Clinical Findings

  • May be suspected in the full-term newborn and in infants up to age 6 months whose chest circumference exceeds the head circumference (unless the child is very obese)

  • May be discovered when the child is examined because of delayed developmental milestones or neurologic problems, such as seizures or spasticity

  • May be a marked backward slope of the forehead (as in familial microcephaly) with narrowing of the bitemporal diameter

  • Eye, cardiac, and bone abnormalities may also be clues to congenital infection


  • Laboratory findings vary with the cause

  • In the newborn, congenital infection may be assessed by

    • IgM antibody titers for toxoplasmosis, rubella, cytomegalovirus (CMV), herpes simplex virus, and syphilis

    • Urine culture for CMV

  • Genetic testing can be targeted based on history and physical examination

  • Most metabolic disorders present either as congenital syndromic microcephaly (ie, dysmorphisms present on examination) or with postnatal microcephaly and global developmental delay

  • Nonsyndromic microcephaly presenting at birth may be due to

    • Maternal PKU (maternal serum with elevated phenylalanine)

    • Phosphoglycerate dehydrogenase deficiency (disorder of L-serine biosynthesis)

    • Amish lethal microcephaly (elevated urine alpha-ketoglutaric acid)

  • CT or MRI scans

    • May demonstrate calcifications, malformations, or atrophic patterns that suggest specific congenital infections or genetic syndromes

    • MRI is most helpful in definitive diagnosis, prognosis, and genetic counseling

  • Plain skull radiographs are of limited value


  • Genetic counseling should be offered to the family of any infant with significant microcephaly

  • Individuals may need screening for vision and hearing abnormalities as well as supportive therapies for developmental delay

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