Microcephaly

Microcephaly (from

There is no specific treatment that returns the head size to normal.[3] In general, life expectancy for individuals with microcephaly is reduced, and the prognosis for normal brain function is poor. Occasional cases develop normal intelligence and grow normally (apart from persistently small head circumference).^[3][9] It is reported that in the United States, microcephaly occurs in 1 in 800-5,000 births.^[4]

Signs and symptoms

There are a variety of symptoms that can occur in children.

Microcephaly is a type of cephalic disorder. It has been classified in two types based on the onset:^[13]

Congenital

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• Isolated
  1. Familial (
     autosomal recessive) microcephaly^[14]
  2. Autosomal dominant microcephaly^[15][16]
  3. X-linked microcephaly^[14]
  4. Chromosomal (balanced rearrangements and ring chromosome)
• Syndromes
  • Chromosomal
    1. Poland syndrome^[17]
    2. Down syndrome^[18]
    3. Edward syndrome^[19]
    4. Patau syndrome^[20]
    5. 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. Dihydropteridine reductase deficiency - in up to 25% of patients^[21]
  5. 5,10-methenyltetrahydrofolate synthetase deficiency
  6. Holoprosencephaly
  7. Primary microcephaly^[22]
  8. Wiedemann-Steiner syndrome
• Acquired
  • Disruptive injuries
    1. Ischemic stroke^[23]
    2. Hemorrhagic stroke^[23]
    3. Death of a monozygotic twin
  • Vertically transmitted infections
    1. Congenital cytomegalovirus infection^[24]
    2. Toxoplasmosis^[24]
    3. Congenital rubella syndrome^[24]
    4. Congenital varicella syndrome^[24]
    5. Zika virus (see Zika fever#Microcephaly)^[25]
  • Drugs
    1. Fetal hydantoin syndrome^[24]
    2. Fetal alcohol syndrome^[24]
• Other
  1. Radiation exposure to mother
  2. Maternal malnutrition^[24]
  3. Maternal phenylketonuria^[24]
  4. Poorly controlled gestational diabetes
  5. Hyperthermia
  6. Maternal hypothyroidism
  7. Placental insufficiency
  8. Craniosynostosis^[24]

Postnatal onset

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• Genetic
  • Inborn errors of metabolism
    1. Congenital disorder of glycosylation^[26]
    2. Mitochondrial disorders^[27]
    3. Peroxisomal disorder^[28]
    4. Glucose transporter defect^[29]
    5. Menkes disease
    6. Congenital disorders of amino acid metabolism^[30]
    7. Organic acidemia^[31]
• Syndromes
  • Contiguous gene deletion
    1. 17p13.3 deletion (Miller–Dieker syndrome)^[32]
  • 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
• Acquired
  • Disruptive injuries
    1. Traumatic brain injury^[33]
    2. Hypoxic-ischemic encephalopathy^[24]
    3. Ischemic stroke^[23]
    4. Hemorrhagic stroke^[23]
  • Infections
    1. Congenital
       HIV encephalopathy^[34]
    2. Meningitis^[35]
    3. Encephalitis^[36]
  • Toxins
    • Chronic kidney failure^[37]
  • Deprivation
    1. Hypothyroidism^[38]
    2. Anemia^[39]
    3. Congenital heart disease^[40]
    4. Malnutrition^[41]

Genetic mutations cause most cases of microcephaly.

The spread of Aedes mosquito-borne Zika virus has been implicated in increasing levels of congenital microcephaly by the International Society for Infectious Diseases and the US Centers for Disease Control and Prevention.^[46] Zika can spread from a pregnant woman to her fetus. This can result in other severe brain malformations and birth defects.^{[47][48][49][50]} A study published in The New England Journal of Medicine has documented a case in which they found evidence of the Zika virus in the brain of a fetus that displayed the morphology of microcephaly.^[51]

Microlissencephaly

Intracranial volume also affects this pathology, as it is related with the size of the brain.[58]

Pathophysiology

Microcephaly generally is due to the diminished size of the largest part of the human brain, the

There is no known cure for microcephaly.

People with small heads were displayed as a public spectacle in ancient Rome.^[69]

People with microcephaly were sometimes sold to

• 
  Triboulet, a French court jester, 1461
• 
  18-year-old Emil R., 1868
• 
  Elderly female, 1888/89
• 
  36-year-old male, 1894 (normal intelligence present)
• 
  52-year-old female, 1900
• 
  10-year-old male, 1904
• 
  20-year-old female, 1906/07
• 
  3 relatives, 1913
• 
  18-year-old sister and 9-year-old brother, 1917
• 
  55-year-old female, 1920 (linear descendant of Pocahontas)
• 
  6 siblings, 1920

Notable cases

• A 'dwarf' of Punt (ancient Somalia) was given by the Chief clans as partial tribute to the last ruler of Ancient Egypt's Old Kingdom,
  Harkhuf! The men in your service [escorts; soldiers; sailors; guards, etc.] ought pay sincere care with the dwarf's head while sleeping during the voyage to the palace" (so that it does not fall off). At the same time, it could be for other reasons unrelated to microcephaly, etc.^[73]
• Triboulet, a jester of duke René of Anjou (not to be confused with the slightly later Triboulet at the French court).
• Jenny Lee Snow and Elvira Snow, whose stage names were Pip and Flip, respectively, were sisters with microcephaly who acted in the 1932 film Freaks.
• Schlitze "Schlitzie" Surtees, possibly born Simon Metz, was a widely known sideshow performer and actor, who also appeared in Freaks.
• Lester "Beetlejuice" Green, a member of radio host Howard Stern's Wack Pack.

See also

• Anencephaly (Usually rapidly fatal)
• Cerebral rubicon
• Hydrocephaly
• Macrocephaly
• Seckel syndrome
• Achalasia microcephaly

References