Aicardi syndrome is a rare genetic disorder affecting only girls.Even though the exact genetic cause is not yet known, there are strong clues, which are currently researched further.
Signs and Symptoms
Aicardi syndrome is a rare genetic disorder which primarily affects newborn girls. The syndrome is not known to pass from parent to child, i.e. the condition is sporadic. Classically, the syndrome was characterized by three features:
- Absence of the corpus callosum, a brain structure that links the two brain hemispeheres.
- Lesions in the retina of the eye that are quite specific to this disorder.
- Infantile spasms, meaning seizures in young children.
Lately, however, it is becoming clear that there are other symptoms that are specific for this disorder, including microcephaly (small brain), a low axial muscle tone (meaning low muscle tone in the parts of the body attached to the spinal cord, such as the head, trunk and pelvis) and a high muscle tone in the limbs.
Genetics of the Disorder
Since newborn girls are primarily affected by this condition, it is thought that the disease-causing gene or genes is/are found on the X chromosome, which is supported by the observation that the only boys that have ever been diagnosed with the disorder suffered from Klinefelter syndrome (instead of XY, like regular males, they posses XXY as sex chromosomes).
Aicardi syndrome is believed to be caused by a dominant X-linked mutant gene and follows an X-linked dominant pattern in its inheritance. That being said, there are no known causes of parent-child transmission of the syndrome, so scientists think that all cases of the disorder are caused by new mutations.
Aicardi syndrome is usually identified before the child reaches the age of five months. Until about three months of age, the development of the child follows a normal route, but then the affected child begins to experience infantile spasms. Almost all affected individuals experience developmental delays, with the majority facing moderate to severe mental retardation. The survival of affected individuals is highly variable, with an age range that lies between birth and their late forties. The mean age of death is about eight and a half years.
Prevalence and Treatment
As mentioned before, it is a quite rare syndrome. Even though the exact prevalence is unknown, it has been estimated that there are about 850 cases in the US and about 4000 worldwide, which would correspond with a prevalence of roughly 1 in each 100.000 to 150.000 births.
At present there is no known cure for the syndrome. Treatment mostly involves management of the seizures and early and continuing programs of intervention for develomepmental delays. Currently, research is being done to accurately describe the actual cause of this disorder, most notably at the university of California and the Baylor College of Medicine (see references).