Microcephaly is a rare cephalic condition when the child’s head is significantly smaller than it should be. It affects approximately 2-12 babies per 10000 live births in the USA every year.
Microcephaly is a birth defect, when a baby’s head is small in comparison with the heads of children of the same sex and age. Microcephaly can be primary which is called microcephaly vera or develop secondary to cerebral disease. Another classification distinguishes congenital (innate, existing before or at the birth) or acquired. The disorder may be present at birth or appear during the first few years of life.
The defect has numerous possible causes. A big range of genetic and environmental factors can disturb the development of the skull and nervous system. It is usually not a disease, rather a symptom of another condition.
Genetic conditions that present the microcephaly are inherited sex-linked (linked to X- or Y- chromosome) or autosomal recessive (linked to non-sex chromosomes). The isolated microcephaly occurs as a familial microcephaly, autosomal dominant microcephaly, X-linked microcephaly and other chromosomes abnormalities. Other syndromes accompanied by microcephaly are: Poland syndrome (unknown etiology), Down syndrome (trisomy 21/third copy of the chromosome 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), Wolf–Hirschhorn syndrome (partial deletion of chromosomal material the short arm of chromosome 4), Cri du chat syndrome (deletion on the short arm of the chromosome 5), Williams syndrome (deletion of genes from the long arm of chromosome 7), DiGeorge syndrome (deletion of the chromosome 22) and many others.
Sometimes the cranial sutures are tending to close prematurely causing craniosynostosis.
Microcephaly is known to be caused by the prenatal disturbance of the child’s development. The cerebral anoxia (decreased oxygen supply to the fetal brain provoked by the placental insufficiency), infection diseases during pregnancy such as cytomegalovirus, rubella (measles), varicella (chickenpox), Zika virus, toxoplasmosis, drugs and alcohol abuse during pregnancy and another maternal health disorders lead to microcephaly.
Microcephaly may develop when a child is older due traumatic brain injury, haemorrhage or stroke in the newborn, infections of the nervous system (meningitis, encephalitis) etc.
Exposure to radiation, toxins, drugs and medicaments, alcohol abuse and infections especially ones acquired during pregnancy are putting the fetus’s development into risk. Some mother’s diseases may also affect the child such as gestational diabetes, phenylketonuria, hyperthermia and hypothyroidism. For a new organism to develop in the womb normally the proper nutrition of the mother is vital. Chronic infection diseases of the mother such as HIV, syphilis, herpes virus were reported to disrupt the growth of the fetus.
If the woman has experienced miscarriages or faced the difficulties to conceive a baby she should be carefully examined to exclude infections, genetic disorder or any other diseases.
The main symptom of the condition is a diminished skull’s circumference (the distance around the top of the head).
In contrast to the small size of the skull the face is of normal size, the forehead is narrow and sharply recedes, while the occipital part is flat.
Usually microcephaly reduces the brain size – affected person’s brain often weights less than 300 g (the normal brain weight in adult is 1100 g – 1500 g). Other symptoms depend on the main reason of the defect and may vary from child to child. Among them may be present: failure to thrive, spasticity (involuntary muscle contractions), impaired motor function, mental and psychomotor retardation, seizures, sight loss and hearing problems, joint and skeleton deformities (including dwarfism – short stature).
Affected children can be recognized before the birth during ultrasound scanning, right after the labor or lately by the characteristic features, low intelligence and physical retardation.
Using standardized growth charts, the measurement of the head’s size is compared with other children’s measurements in percentiles. In children with microcephaly, head size measures essentially below average, even below the first percentile for child’s age and sex.
Sometimes other tests are required to determine the underlying cause of the defect and find proper treatment for the disturbed nervous system development. These include blood and urine testing, X-ray, CT or MRI, genetic tests.
There is no specific treatment for the condition except the surgery for craniosynostosis.
The treatment of the child is focused on prevention or decreasing the possible neurological deficit, motor and mental retardation. Patients get symptomatic drugs administration. Parents along with the child learn to manage the condition and improve the health of their baby.