It remains unclear how a reduced amount of this protein disrupts early development and causes the characteristic features of Greig cephalopolysyndactyly syndrome.This condition is inherited in an autosomal dominant pattern, which means the defective gene is located on an autosome, and only one copy of the defective GLI3 gene is sufficient to cause the disorder. In cases of dominant inheritance, an affected person inherits the genetic mutation or chromosomal abnormality from one affected parent.Rare instances of this disorder are sporadic, and occur in people with no history of the condition in their family. Diagnosis
The disease is not easily definable. The main form of diagnosis is presumptive, if the person has the usual triad of preaxial polydactyly with cutaneous syndactyly of at least one limb, macrocephaly, and  hypertelorism. However, a definitive diagnosis can be made if there is a phenotype that is caused by a Gcps and a Gli3 gene mutation. It can also be made if the person has a family member or relative with the disease. Possibly, antenatal ultrasound can detect macrocephaly, and a high-resolution ultrasound can detect polydactyly and syndactyly. There are a lot of differential diagnoses, including over 100 syndromes and disorders that can cause polydactyly. However, there are a few diseases with an overlap that is significant. These diseases include: acrocallosal syndrome, carpenter syndrome, and Gorlin syndrome. Management
The main treatment is surgery to fix the abnormalities in the limbs, like syndactyly.
It is less important to repair the feet surgically, as it can cause complications, and it is not aesthetically important compared to the hands. If there is polydactyly with an extra digit that is fully functional, then the digit can stay. Some people may have intellectual disability, though this condition usually causes only mild impairment. Developmental assistance and early specialist intervention should be offered in the case of intellectual disability. People should be tested as an individual and be given proper assistance. Prognosis
The outlook is usually good in the usual case of GCPS. Mostly, the biggest problem associated with the condition in mild intellectual impairment. Eponym
The condition is named for David Middleton Greig FRSE. References
External links
Greig cephalopolysyndactyly syndrome at NLM Genetics Home Reference
GeneReview/NIH/UW entry on Greig Cephalopolysyndactyly Syndrome