Microcephaly

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.

Microencephaly
This is a disorder characterized by a small head and may be caused by a disturbance in the rapid growing of nerve cells. The term "microencephaly" is used to specifically denote a small brain. ("Cephalus" denotes the head, and "encephalon" denotes the brain.) In ICD-10, "Microcephaly" is classified under "congenital malformations of the nervous system", as opposed to macrocephaly which is classified under "congenital malformations and deformations of the musculoskeletal system".

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

In these contexts, it can be considered a craniofacial abnormality.
 * alcoholism (which can result in the fetal alcohol syndrome disability)
 * diabetes
 * varicella zoster virus (Chickenpox)
 * rubella (German measles)
 * radiation. After the dropping of atomic bombs on Hiroshima and Nagasaki, a women in close proximity to Ground Zero who had been pregnant at the time gave birth to children with microcephaly.

In the last case, a total of 7 of the in utero children at Hiroshima were affected. This was out of the entire city of Hiroshima, a city with normal war-time pregnancy rates, meaning it did not affect hundreds or thousands of in utero children at all. However, microcephaly prevalence was 7 out of a group of 11 pregnant women who held the distinction of surviving the blast at an astonishing close distance of ~1 km from Ground Zero. Due to their close proximity to the bomb, the pregnant women's in utero children received a biologically significant radiation dosage that was relatively high due to the uniquely massive neutron output of Little Boy. The massive neutron output of the lower explosive-yielding Little Boy bomb at Hiroshima was much higher than that of the more destructive, higher explosive yielding Fat Man bomb at Nagasaki. This discrepancy is due to vast differences in their respective designs. Microcephaly is the only proven malformation, or congenital abnormality, found in the children of Hiroshima and Nagasaki.

Presentation
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.

Microcephaly and culture
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. Famous examples are Zip the Pinhead (although he may not have had microcephaly) and Schlitzie the Pinhead, 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.]