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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/08/21 16:42:13」(JST)

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Microcephaly is a neurodevelopmental disorder in which the circumference of the head is more than two standard deviations smaller than average for the person's age and sex. 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. Two copies of a loss-of-function mutation in one of the microcephalin genes causes primary microcephaly.

In general, life expectancy for individuals with microcephaly is reduced and the prognosis for normal brain function is poor. The prognosis varies depending on the presence of associated abnormalities.

Causes

Microcephaly is a type of cephalic disorder.

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.^[1]^[2]^[3]

Microencephaly

"Microcephaly" means "small head". "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.^[4]

Other

Microcephaly can also be associated with other conditions that are only indirectly associated with the nervous system:

alcoholism (which can result in the fetal alcohol syndrome disability)
diabetes
varicella zoster virus (Chickenpox)
rubella (German measles)
CMV (Cytomegalovirus)
radiation

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.^[5] 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.^[6] Microcephaly is the only proven malformation, or congenital abnormality, found in the children of Hiroshima and Nagasaki.^[6]

Presentation

17-year old boy with microcephaly

Affected newborns generally have striking neurological defects and seizures. Severely impaired intellectual development is common, but disturbances in motor functions may not appear until later in life.

Infants with microcephaly are born with either a normal or reduced head size. Subsequently the head fails to grow while the face continues to develop at a normal rate, producing a child with a small head and a receding forehead, and a loose, often wrinkled scalp. As the child grows older, the smallness of the skull becomes more obvious, although the entire body also is often underweight and dwarfed. Development of motor functions and speech may be delayed. Hyperactivity and mental retardation are common occurrences, although the degree of each varies. Convulsions may also occur. Motor ability varies, ranging from clumsiness in some to spastic quadriplegia in others.

Prognosis

Generally there is no specific treatment for microcephaly. Treatment is symptomatic and supportive.

Microcephalics were sometimes sold to freak shows in North America and Europe in the 19th and early 20th century, where they would go under the name pinheads. Many of them were presented as different species (e.g., "monkey man") and described as being the missing link, but it was also common for them to be presented as the last surviving Aztec.^[7] Famous examples are Zip the Pinhead (although he may not have had microcephaly)^[8] and Schlitzie the Pinhead,^[9] who also starred in the 1932 movie Freaks.

Notable microcephalic persons

Schlitzie, a circus performer best known for his role in the 1932 film Freaks.
Beetlejuice, a member of Howard Stern's "Wack Pack".
Zip the Pinhead (Circus "freak show" performer William Henry Johnson) is commonly associated with microcephaly, although he may not have actually had it.
Triboulet was a jester of kings Louis XII and Francis I of France. He appears in Victor Hugo's Le Roi s'amuse and its opera version, Giuseppe Verdi's Rigoletto.

References

^ Crespi B, Stead P, Elliot M (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. doi:10.1073/pnas.0906080106. PMC 2868282. PMID 19955444. http://www.pnas.org/content/107/suppl.1/1736.full.
^ "Rare chromosomal deletions and duplications increase risk of schizophrenia". Nature 455 (7210): 237–41. September 2008. doi:10.1038/nature07239. PMID 18668038.
^ 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. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2902282.
^ David D. Weaver; Ira K. Brandt (1999). Catalog of prenatally diagnosed conditions. JHU Press. p. 104. ISBN 978-0-8018-6044-7. http://books.google.com/books?id=m2Mx9KyY-igC&pg=PA104. Retrieved 25 March 2012.
^ Hiroshima Peace Site
^ ^a ^b Teratology in the Twentieth Century Plus Ten
^ Mateen FJ, Boes CJ. ""Pinheads": the exhibition of neurologic disorders at "The Greatest Show on Earth"". Neurology 30: 2028–32. doi:10.1212/WNL.0b013e3181ff9636. PMID 21115959.
^ "[1]?" 16 October 2010.
^ "[2]?" 16 October 2010.

External links

microcephaly at NINDS
Microcephaly Support Group
The Rat People of Pakistan
NINDS Overview
Schlitzie The Pinhead

English Journal

A human iPSC model of Ligase IV deficiency reveals an important role for NHEJ-mediated-DSB repair in the survival and genomic stability of induced pluripotent stem cells and emerging haematopoietic progenitors.

Tilgner K, Neganova I, Moreno-Gimeno I, Al-Aama JY, Burks D, Yung S, Singhapol C, Saretzki G, Evans J, Gorbunova V, Gennery A, Przyborski S, Stojkovic M, Armstrong L, Jeggo P, Lako M.Source1] Institute of Genetic Medicine, International Centre for Life, Newcastle University, Newcastle, UK [2] NESCI, Newcastle University, Newcastle, UK.
Cell death and differentiation.Cell Death Differ.2013 Aug;20(8):1089-100. doi: 10.1038/cdd.2013.44. Epub 2013 May 31.
DNA double strand breaks (DSBs) are the most common form of DNA damage and are repaired by non-homologous-end-joining (NHEJ) or homologous recombination (HR). Several protein components function in NHEJ, and of these, DNA Ligase IV is essential for performing the final 'end-joining' step. Mutations
PMID 23722522

Recent advances in the genetic etiology of brain malformations.

Dyment DA, Sawyer SL, Chardon JW, Boycott KM.SourceDepartment of Genetics, Children's Hospital of Eastern Ontario, 401 Smyth Road, Ottawa, ON, Canada, K1H 8L1.
Current neurology and neuroscience reports.Curr Neurol Neurosci Rep.2013 Aug;13(8):364. doi: 10.1007/s11910-013-0364-1.
In the past few years, the increasing accessibility of next-generation sequencing technology has translated to a number of significant advances in our understanding of brain malformations. Genes causing brain malformations, previously intractable due to their complex presentation, rarity, sporadic o
PMID 23793931

Molecular karyotyping of an isolated partial trisomy 11q patient with additional findings.

Kayhan G, Cavdarli B, Yirmibes Karaoguz M, Percin EF, Oztürk Kaymak A, Biri A, Ergun MA.SourceGazi University Faculty of Medicine, Department of Medical Genetics, Besevler, Ankara, Turkey. Electronic address: gulsum-kayhan@hotmail.com.
Gene.Gene.2013 Jul 25;524(2):355-60. doi: 10.1016/j.gene.2013.04.053. Epub 2013 May 1.
Isolated partial duplication of the long arm of chromosome 11 is very rare. The main features are dysmorphic facial features, pre/postnatal growth retardation, speech delay, mental retardation, hypotonia, microcephaly, and cardiac, vertebral, limb and genital anomalies. In this case, we report a pat
PMID 23644025

Japanese Journal

滋賀県犬上川下流域におけるハリヨGasterosteus aculeatus microcephalusの季節消長と生息場所利用

上野篤史,金尾滋史,久米学 [他]
地域自然史と保全 = Bulletin of Kansai Organization for Nature Conservation 34(1), 3-12, 2012-06
NAID 40019793050

滋賀県犬上川下流域におけるハリヨGasterosteus aculeatus microcephalusの季節消長と生息場所利用

上野篤史,金尾滋史,久米学,近雅博
関西自然保護機構会報 34(1), 3-12, 2012-06
NAID 110009432950

日本と南シナ海から得られたニギス科ニギス属の新種ツマリニギス(新称)

Endo Hiromitsu,Nashida Kazuya
Bulletin of the National Museum of Nature and Science. Series A, Zoology (Suppl.6), 17-26, 2012-03
NAID 40019531126

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