In Microcephaly there is sub-optimal growth of the brain which causes it to be smaller than usual. At or after birth, microcephaly is detected by measuring the head circumference. Detailed brain imaging, such as a magnetic resonance scan, may demonstrate an alteration in brain structure, for example, a decrease in the number and complexity of the folds on the surface of the brain (see entry, Lissencephaly). However, quite frequently, the brain scan appearance simply confirms reduction in overall size of the brain that is otherwise normally formed. Children and adults who are affected by microcephaly have variable neurological impairments, from very mild learning difficulties (see entry, Learning Disability) to much more severe problems including feeding difficulties, profound learning disability, epilepsy and spasticity (see entry, Cerebral Palsy).

Microcephaly may be caused by many different conditions that may be genetic or entirely non-genetic in origin. For example, genetic causes include different chromosome disorders, different single gene abnormalities and specific genetic syndromes. Non-genetic causes include infections contracted by the baby in the womb (intrauterine infections), reduction in blood supply to the developing fetal brain during pregnancy and some post-natal infections or traumas.

Intrauterine infections which can cause Microcephaly include Cytomegalovirus (CMV) , Toxoplasmosis and Rubella (German measles).

Rare syndromes which cause disturbed brain development and Microcephaly, usually with other physical disabilities, include Cornelia De Lange syndrome , Rubinstein Taybi syndrome and Seckel syndrome.

Inheritance patterns
Complexity arises because different inheritance patterns of genetic Microcephaly are possible. It is known that faults in the function of many different genes may cause genetic Microcephaly. In autosomal dominant Microcephaly, there is one affected parent who has fifty per cent chance of transmitting the gene fault to each child they may have. In autosomal recessive Microcephaly, both parents are unaffected but both carry a single, recessive Microcephaly gene. It is only when both parents transmit this gene to their child (twenty-five per cent risk of this happening) that the child will be affected by Microcephaly. In X-chromosome linked Microcephaly, an unaffected mother who carries an X-chromosome linked Microcephaly gene has a twenty-five per cent chance of having a son who is affected by Microcephaly. Of these three different inheritance mechanisms, autosomal recessive Microcephaly is probably the most common and this condition is most often characterized by microcephaly that is present at birth and learning disability that is non-progressive.

Prenatal diagnosis
It is unusual for genetic Microcephaly to be diagnosed by ultrasound scan in early pregnancy but a reduction in fetal brain growth may be discovered by scans undertaken during in the last few months of pregnancy. A number of Microcephaly genes have been discovered but it is rare for any of these to be detected in an affected child. The most common gene defects are found in the ASPM gene, also called MCPH5, and laboratory diagnostic DNA tests for this condition are being introduced at present.

Medical text written May 2002 by Dr J Tolmie. Last updated August 2006 by Dr J Tolmie, Consultant Clinical Geneticist, Ferguson-Smith Centre for Clinical Genetics, Glasgow, UK.

Further Online Resources
Medical texts in The Contact a Family Directory are designed to give a short, clear description of specific conditions and rare disorders. More extensive information on this condition can be found on a range of reliable, validated web sites and links to them are included in the CD-ROM version of this Directory. Further information on these resources can be found in our Medical Information on the Internet article.

Microcephaly Support Group
PO Box 519
Pinner HA5 9DR
Tel: 01638 552689
e-mail: gill@microcephaly.org.uk
Web: http://www.microcephaly.co.uk

This is a small parent support group re-established in 2002. The group offers support and information by letter, telephone and email. It publishes a regular newsletter 'Connections' and is in touch with approximately 300 families.

Group details last updated January 2007.