Microcephaly is a neurological disorder where the distance around the largest portion of the head (the circumference) is less than should normally be the case in an infant or a child. The condition can be evident at birth, or can develop within the first few years following birth. The smaller than normal head restricts the normal growth and development of the brain.
The word microcephaly comes from the Greek micros meaning small, and kephale meaning head. The small head circumference that is a hallmark of microcephaly has been defined as that which is either two or three standard deviations (a statistical measure of variability) below the normal average head circumference for the age, gender, and race of the child. Put another way, the head size is markedly smaller than the expected size for about 97–99% of other children.
The condition can be present at birth or may develop during the first few years of life. In the latter situation, the growth of the head fails to keep to a normal pace. This produces a small head, relatively large face (since the face keeps growing at a normal rate), and a forehead that slopes backward. The smallness of the head becomes even more pronounced with age. An older child with microcephaly also has a body that is smaller and lighter than normal. This may be a consequence of the restricted brain development.
Microcephaly is a rare neurological condition and occurs worldwide. Little detailed information on the prevalence of the disorder is available. Microcephaly does not appear to be more prevalent among any race or one gender.
Causes and symptoms
Microcephaly may have a genetic basis. If the gene defect(s) are expressed during fetal development, the condition is present at birth. This is the congenital form of the disorder. The microcephaly that develops after birth may still reflect genetically based developmental defects. As well, the delayed microcephaly can be caused if the normal openings in the skull close too soon after birth, preventing normal head growth. This condition is also referred to as craniosynostosis .
Other possible causes of microcephaly include infections during pregnancy (rubella, cytomegalovirus, toxoplasmosis), adverse effects of medication, and the
excessive use of alcohol by the mother during pregnancy (fetal alcohol syndrome).
The damage from microcephaly comes because of the cramped interior of the skull. This lack of space exerts pressure on the growing brain. This causes impairment and delayed development of functions such as speech and control of muscles. The impaired muscle control can produce effects ranging from a relatively minor clumsiness in body movement to the more serious and complete loss of control of the arms and legs. A child can also be hyperactive and mentally retarded, although the latter is not always present. As a child grows older, seizures may occur.
It should be noted that at times it is diminished growth of the brain that results in microcephaly. Without proper brain growth, the surrounding skull does not expand and microcephaly results.
Diagnosis of craniosynostosis and microcephaly is made by a physician, typically during examination after birth. A physician may also be alerted to the presence of microcephaly based on the appearance of the head at birth. Other clues in the few years after birth can be the failure to achieve certain developmental milestones, and the appearance of the distinctive facial appearance.
The medical treatment team can consist of family and more specialized physicians and nurses. Parents and care-givers play an important role in supportive care. As various developmental challenges present themselves, physical therapists and special education providers may become part of the treatment team.
In the case of craniosynostosis, surgery can be accomplished to reopen the prematurely closed regions of the skull. This allows the brain to grow normally. There is no such treatment for the congenital form of microcephaly. Treatment then consists of providing for the person's comfort and strategies to compensate for physical and mental delays.
Recovery and rehabilitation
Recovery from craniosynostosis can be complete if surgery is done at an early enough age. For a child with other forms of microcephaly, few treatment options are available. Emphasis, therefore, is placed upon maximizing mobility and mental development, rather than recovery. Speech therapists and audiologists can help with hearing and language development. Physical and occupational therapists provide aid in walking and adaptive equipment such as wheelchairs. Special education teachers coordinate educational goals and strategies based upon the child's abilities.
Although as of April 2004, there are no ongoing clinical trials underway for the study or treatment of microcephaly, research is being done to explore and understand the mechanisms, particularly genetic, of brain and skull development. By understanding the nature of the developmental malfunctions, it is hoped that corrective or preventative strategies might be developed.
With surgery, the prognosis for children with craniosynostosis can be good. However the outlook for children with other forms of microcephaly is poor, and the likelihood of having normal brain function is likewise poor.
As microcephaly is often associated with chromosomal abnormalities, the specific genetic cause for a person's microcephaly should be determined, if possible. Genetic counseling is available to help parents with information about their child with microcephaly and to plan for future pregnancies.
Woods, C. G. "Human microcephaly." Current Opinions in Neurobiology (February 2004): 112–117.
National Institute of Neurological Disorders and Stroke. NINDS Microcephaly Information Page. <http://www.ninds.nih.gov/health_and_medical/disorders/microcephaly.htm> (April 9, 2004).
National Institute for Neurological Diseases and Stroke (NINDS). 6001 Executive Boulevard, Bethesda, MD 20892. (301) 496-5751 or (800) 352-9424. <http://www.ninds.nih.gov>.
National Institute for Child Health and Human Development (NICHD). 31 Center Drive, Rm. 2A32 MSC 2425, Bethesda, MD 20892-2425. (301) 496-5133; Fax: (301) 496-7101. <http://www.nichd.nih.gov>.
National Organization for Rare Disorders. 55 Kenosia Avenue, Danbury, CT 06813-1968. (203) 744-0100 or (800) 999-6673; Fax: (203) 798-2291. [email protected] <http://www.rarediseases.org>.
Brian Douglas Hoyle, PhD
"Microcephaly." Gale Encyclopedia of Neurological Disorders. . Encyclopedia.com. (September 23, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/microcephaly
"Microcephaly." Gale Encyclopedia of Neurological Disorders. . Retrieved September 23, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/microcephaly
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