Due to their proximity to the bomb, the pregnant womens in utero children received a biologically significant radiation dose that was relatively high due to the massive neutron output of the lower explosive-yielding Little Boy. Researchers studied 286 additional children who were in utero during the atomic bombings, and after a year they found these children had a higher incidence of microcephaly and mental retardation. Other relations
Intracranial volume also affects this pathology, as it is related with the size of the brain. Pathophysiology
Microcephaly generally is due to the diminished size of the largest part of the human brain, the cerebral cortex, and the condition can arise during embryonic and fetal development due to insufficient neural stem cell proliferation, impaired or premature neurogenesis, the death of neural stem cells or neurons, or a combination of these factors. Research in animal models such as rodents has found many genes that are required for normal brain growth. For example, the Notch pathway genes regulate the balance between stem cell proliferation and neurogenesis in the stem cell layer known as the ventricular zone, and experimental mutations of many genes can cause microcephaly in mice, similar to human microcephaly. Mutations of the abnormal spindle-like microcephaly-associated (ASPM) gene are associated with microcephaly in humans and a knockout model has been developed in ferrets that exhibits severe microcephaly. In addition, viruses such as cytomegalovirus (CMV) or Zika have been shown to infect and kill the primary stem cell of the brain—the radial glial cell, resulting in the loss of future daughter neurons.
Notable cases
A dwarf of Punt (ancient Somalia) was given by the Chief clans as partial tribute to the last ruler of Ancient Egypts Old Kingdom, Pepi II Neferkare (6th Dynasty, circa 2125–2080 BC); it could be inferred that this person was also microcephalic. In a letter preserved at the British Museum, the young king gives instructions by letter, "Harkhuf! The men in your service [escorts; soldiers; sailors; guards, etc.] ought pay sincere care with the dwarfs 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. 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 Sterns Wack Pack. See also
Anencephaly (Usually rapidly fatal)
Cerebral rubicon
Hydrocephaly
Macrocephaly
Seckel syndrome
Achalasia microcephaly

References
External links

Microcephaly at NINDS
NINDS Overview