Various factors are said to cause microcephaly. These include environmental hazards which the pregnant mother was exposed to, genetic defects passed on by parents to the child, and infections acquired by the mother while in the first few months of pregnancy.
The defective gene in microcephaly is the microcephalin gene which codes for proteins involved in the cell cycle and repair of DNA. There are six microcephaline genes, MCPH1 to MCPH6. MCPH1 is responsible for regulating the brain size of the fetus. Mutations or deletions in the nuclear proteins of MCPH1 causes premature condensation of chromosomes resulting in the arrest of further cell division. As MCPH1 is important in brain development of embryos, loss of its function leads to the reduction of the size of the brain. Other genes implicated in microcephaly include ASPM, CDK5RAP2 and CENPJ.
Microcephaly is inherited through an autosomal recessive pattern, and rarely, through an autosomal dominant pattern. In autosomal recessive pattern, both parents usually have the defective gene and the child with microcephaly inherits both genes from each parent. In autosomal dominant pattern, the disorder can be inherited from only one parent. Some conditions associated with microcephaly include Cornelia de Lange syndrome,Cri du chat syndrome, Down syndrome and Trisomy 18.
The health status of the mother during the entire course of pregnancy is very important in determining the well being of her unborn child. The first three months, or the first trimester of pregnancy is considered as the most crucial stage. This is when the vital organs of the baby are formed. Microcephaly causes at this very important and sensitive stage of pregnancy include toxoplasmosis, chickenpox and german measles.
The lifestyle habits of the mother during pregnancy may also contribute to the development of microcephaly in infants. Alcoholism can lead to fetal alcohol syndrome which is often manifested by microcephaly. A diabetic and malnourished pregnant woman may also deliver a child with microcephaly. Use of certain drugs such as Phenytoin, and exposure to radiation may also result in microcephaly.