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Classification and external resources
Neural scans of a person without microcephaly (left) and a patient with microcephaly.
ICD-10 Q02
ICD-9 742.1
OMIM 251200
DiseasesDB 22629
MedlinePlus 003272
MeSH D008831

Microcephaly is a neurodevelopmental disorder. It is an important neurologic sign but there is nonuniformity in the definition of microcephaly. It is usually defined as a head circumference (HC) more than 2 standard deviations below the mean for age and gender.[1][2] Some academics advocate defining it as head circumference more than 3 standard deviations below the mean for the age and sex.[3] Microcephaly may be congenital or it may develop in the first few years of life. The disorder may stem from a wide variety of conditions that cause abnormal growth of the brain, or from syndromes associated with chromosomal abnormalities. A homozygous mutation in one of the microcephalin genes causes primary microcephaly.



Microcephaly is a type of cephalic disorder.

It has been classified in two types based on the onset:[4]

1. Congenital


  1. Familial (Autosomal recessive) microcephaly
  2. Autosomal Dominant microcephaly
  3. X-linked microcephaly
  4. Chromosomal ( balanced rearrangements & Ring chromosome)


  • Chromosomal
  1. Down syndrome
  2. Edward Syndrome
  3. Patau Syndrome
  4. Unbalanced rearrangements
  • Contiguous gene deletion
  1. 4p deletion (Wolf–Hirschhorn syndrome)
  2. 5p deletion (Cri-du-chat)
  3. 7q11.23 deletion (Williams syndrome)
  4. 22q11 deletion (DiGeorge syndrome)
  • Single gene defects
  1. Smith–Lemli–Opitz syndrome
  2. Seckel syndrome
  3. Cornelia de Lange syndrome
  4. Holoprosencephaly


  • Disruptive injuries
  1. Ischemic stroke
  2. Hemorrhagic stroke
  3. Death of a monozygotic twin
  • Congenital Infections
  1. Congenital cytomegalovirus infection
  2. Toxoplasmosis
  3. Congenital rubella syndrome
  • Drugs
  1. Fetal hydantoin syndrome
  2. Fetal alcohol syndrome


  1. Radiation exposure to mother
  2. Maternal Malnutrition
  3. Maternal Phenylketonuria
  4. Poorly controlled Gestational diabetes
  5. Hyperthermia
  6. Maternal Hypothyroidism
  7. Placental insufficiency

2. Postnatal onset


  • Inborn errors of metabolism
  1. Congenital disorder of glycosylation
  2. Mitochondrial disorders
  3. Peroxisomal disorder
  4. Glucose transporter defect
  5. Menkes disease
  6. Amino acidopathies
  7. Organic acidemia


  • Contiguous gene deletion
  1. 17p13.3 deletion (Miller–Dieker syndrome)
  • Single gene defects
  1. Rett syndrome (primarily girls)
  2. Nijmegen breakage syndrome
  3. X-linked lissencephaly with abnormal genitalia
  4. Aicardi–Goutières syndrome
  5. Ataxia telangiectasia
  6. Cohen syndrome
  7. Cockayne syndrome


  • Disruptive injuries
  1. Traumatic brain injury
  2. Hypoxic-ischemic encephalopathy
  3. Ischemic stroke
  4. Hemorrhagic stroke
  • Infections
  1. Congenital HIV encephalopathy
  2. Meningitis
  3. Encephalitis
  • Toxins
  1. Lead poisoning
  2. Chronic renal failure
  • Deprivation
  1. Hypothyroidism
  2. Anemia
  3. Congenital heart disease
  4. Malnutrition

A genetic factor may play a role in causing some cases of microcephaly. Relations have been found between autism, duplications of chromosomes and macrocephaly on one side. On the other side a relation has been found between schizophrenia, deletions of chromosomes and microcephaly.[5][6][7] Moreover, an association has been established between common genetic variants within known microcephaly genes (MCPH1, CDK5RAP2) and normal variation in brain structure as measured with MRI (i.e., primarily brain cortical surface area and total brain volume).[8]


"Microcephaly" means "small head" (literal translation from the Greek "μικρό κεφάλι"). "Microencephaly" means "small brain". Because the size of the head is mostly determined by the size of the brain, microencephaly is implied when discussing microcephaly.[9]


After the dropping of atomic bombs on Hiroshima and Nagasaki, several women close to ground zero who had been pregnant at the time gave birth to children with microcephaly.[10] Microcephaly prevalence was 7 out of a group of 11 pregnant women at 11–17 weeks of gestation who survived the blast at less than 1.2 km from ground zero. Due to their proximity to the bomb, the pregnant women's in utero children received a biologically significant radiation dosage that was relatively high due to the massive neutron output of the lower explosive-yielding Little Boy.[11] Microcephaly is the only proven malformation, or congenital abnormality, found in the children of Hiroshima and Nagasaki.[11]







Microcephalics were sometimes sold to freak shows in North America and Europe in the 19th and early 20th century, where they were known by the name "pinheads". Many of them were presented as different species (e.g., "monkey man") and described as being the missing link.[12] Famous examples are Zip the Pinhead (although he may not have had microcephaly)[13] and Schlitzie the Pinhead,[14] who also starred in the 1932 movie Freaks. Both these individuals were cited as influences on the development of the long-running comic strip character Zippy the Pinhead, created by Bill Griffith.[15]

Notable microcephalic persons[edit]

See also[edit]


  1. ^ Leviton, A.; Holmes, L. B.; Allred, E. N.; Vargas, J. (2002). "Methodologic issues in epidemiologic studies of congenital microcephaly". Early Hum Dev 69 (1): 91–105. doi:10.1016/S0378-3782(02)00065-8. 
  2. ^ Opitz, J. M.; Holt, M. C. (1990). "Microcephaly: general considerations and aids to nosology". J Craniofac Genet Dev Biol 10 (2): 75–204. PMID 2211965. 
  3. ^ Behrman, R. E.; Kligman, R. M.; Jensen, H. B. (2000). Nelson's Textbook of Pediatrics (16th ed.). Philadelphia: WB Saunders. ISBN 0721677673. 
  4. ^ Ashwal, S.; Michelson, D.; Plawner, L.; Dobyns, W. B. (2009). "Practice Parameter: Evaluation of the child with microcephaly (an evidence-based review)". Neurology 73 (11): 887–897. doi:10.1212/WNL.0b013e3181b783f7. 
  5. ^ Crespi B, Stead P, Elliot M; Stead; Elliot (January 2010). "Evolution in health and medicine Sackler colloquium: Comparative genomics of autism and schizophrenia". Proc. Natl. Acad. Sci. U.S.A. 107 (Suppl 1): 1736–41. Bibcode:2010PNAS..107.1736C. doi:10.1073/pnas.0906080106. PMC 2868282. PMID 19955444. 
  6. ^ Stone, Jennifer L.; o’Donovan, Michael C.; Gurling, Hugh; Kirov, George K.; Blackwood, Douglas H. R.; Corvin, Aiden; Craddock, Nick J.; Gill, Michael; Hultman, Christina M.; Lichtenstein, Paul; McQuillin, Andrew; Pato, Carlos N.; Ruderfer, Douglas M.; Owen, Michael J.; St Clair, David; Sullivan, Patrick F.; Sklar, Pamela; Purcell (Leader), Shaun M.; Stone, Jennifer L.; Ruderfer, Douglas M.; Korn, Joshua; Kirov, George K.; MacGregor, Stuart; McQuillin, Andrew; Morris, Derek W.; o’Dushlaine, Colm T.; Daly, Mark J.; Visscher, Peter M.; Holmans, Peter A. et al. (September 2008). "Rare chromosomal deletions and duplications increase risk of schizophrenia". Nature 455 (7210): 237–41. Bibcode:2008Natur.455..237S. doi:10.1038/nature07239. PMID 18668038. 
  7. ^ Dumas L, Sikela JM (2009). "DUF1220 domains, cognitive disease, and human brain evolution". Cold Spring Harb. Symp. Quant. Biol. 74: 375–82. doi:10.1101/sqb.2009.74.025. PMC 2902282. PMID 19850849. 
  8. ^ Rimol, Lars M.; Agartz, Ingrid; Djurovic, Srdjan; Brown, Andrew A.; Roddey, J. Cooper; Kahler, Anna K.; Mattingsdal, Morten; Athanasiu, Lavinia et al. (2010). "Sex-dependent association of common variants of microcephaly genes with brain structure". Proceedings of the National Academy of Sciences 107 (1): 384–8. Bibcode:2010PNAS..107..384R. doi:10.1073/pnas.0908454107. JSTOR 40536283. PMC 2806758. PMID 20080800. 
  9. ^ David D. Weaver; Ira K. Brandt (1999). Catalog of prenatally diagnosed conditions. JHU Press. p. 104. ISBN 978-0-8018-6044-7. Retrieved 25 March 2012. 
  10. ^ Hiroshima Peace Site
  11. ^ a b Teratology in the Twentieth Century Plus Ten
  12. ^ Mateen FJ, Boes CJ (2010). ""Pinheads": the exhibition of neurologic disorders at "The Greatest Show on Earth"". Neurology 30 (22): 2028–32. doi:10.1212/WNL.0b013e3181ff9636. PMID 21115959. 
  13. ^ "[1]?" 16 October 2010.
  14. ^ "[2]?" 16 October 2010.
  15. ^ Interview with Bill Griffith, Goblin Magazine 1995, transcribed on zippythepinhead.com; accessed Feb. 13, 2013

External links[edit]