Microcephaly - Causes of Microcephaly

Microcephaly is a medical condition in which theskull becomes more obvious, although the entire
circumference of the head is smaller than normalbody also is often underweight and dwarfed.
because the brain has not developed properly or hasDevelopment of motor functions and speech may be
stopped growing. Microcephaly can be present atdelayed. Hyperactivity and mental retardation are
birth or it may develop in the first few years of life.common occurrences, although the degree of each
It is most often caused by genetic abnormalities thatvaries. Convulsions may also occur. Motor ability
interfere with the growth of the cerebral cortexvaries, ranging from clumsiness in some to spastic
during the early months of fetal development. It isquadriplegia in others.
associated with Down's syndrome, chromosomalCauses of Microcephaly
syndromes, and neurometabolic syndromes. BabiesMicrocephaly can occur alone or in association with
may also be born with microcephaly if, duringother health problems, and may occur from
pregnancy, their mother abused drugs or alcohol,inheritance of an autosomal recessive, or rarely, an
became infected with a cytomegalovirus, rubellaautosomal dominant gene. Acquired microcephaly may
(German measles), or vermicelli (chicken pox) virus,occur after birth due to various brain injuries such as
was exposed to certain toxic chemicals, or hadlack of oxygen or infection.
untreated phenylketonuria (PKU). Babies born withMicrocephaly may be inherited but the gene is
microcephaly will have a smaller than normal headconsidered to be extremely rare. In the general
that will fail to grow as they progress throughpopulation, microcephaly due to genetic factors
infancy.occurs in 1 in 30,000 to 50,000 live births, and in 1 per
In many cases, microcephaly may not be evident by10,000 births due to other causes. In some
ultrasound until the third trimester, and, therefore,populations, frequency may be as high as 1 in 2,000
may not be seen on ultrasounds performed earlier inbirths.
pregnancy. The diagnosis of microcephaly may beMicrocephaly can also be caused if the mother has an
made at birth or later in infancy. The baby's headinfection while pregnant or if she is exposed to
circumference is much smaller than normal. During theharmful substances during early pregnancy, such as
physical examination, the physician obtains a completex-rays (a type of energy) or chemicals. Another
prenatal and birth history of the child. In older babiescause of microcephaly is if the bones of the skull
and children, the physician may also ask if there is acome together too early. For genetic (inherited)
family history of microcephaly or other medicalcauses of microcephaly, see the next section.
problems. The physician will also ask aboutMicrocephaly is either caused by exposure to harmful
developmental milestones since microcephaly can besubstances during the fetal development, or it may
associated with other problems, such as mentalbe associated with genetic problems or syndromes
retardation.that may have a tendency to run in families.
Infants with microcephaly are born with either aMicrocephaly most often occurs because of failure of
normal or reduced head size. Subsequently the headthe brain to grow at a normal rate. Skull growth is
fails to grow while the face continues to develop atdetermined by brain expansion, which takes place
a normal rate, producing a child with a small head andduring the normal growth of the brain during
a receding forehead, and a loose, often wrinkledpregnancy and infancy.
scalp. As the child grows older, the smallness of the