There are variants of Rett syndrome and two of the better known ones are CDKL5 and FOXG1. Both have similar symptoms and presentations to Rett syndrome so diagnosis should be through genetic testing.
What is CDKL5 Disorder?
CDKL5 is a rare X-linked genetic disorder that results in early onset, difficult to control, seizures, and severe neuro-developmental impairment. CDKL5 is classed as a rare disease.
The CDKL5 gene provides instructions for making a protein that is essential for normal brain development. Although little is known about the protein’s function, it may play a role in regulating the activity of other genes, including the MECP2 gene (the Rett syndrome gene). The CDKL5 protein acts as a kinase, which is an enzyme that changes the activity of other proteins by adding oxygen and phosphate atoms (a phosphate group) at specific positions. Researchers have not yet determined which proteins are targeted by the CDKL5 protein.
Most children affected by CDKL5 suffer from seizures that begin in the first few months of life. Most cannot walk, talk or feed themselves, and many are confined to wheelchairs, dependent on others for everything. Many also suffer with scoliosis, visual impairment, sensory issues and various gastrointestinal difficulties. As time has gone on it appears that there might be other symptoms that play a role in the condition.
What is FOXG1?
The FOXG1 gene provides instructions for making a protein known as forkhead box G1. This protein is a transcription factor, which means it helps regulate the activity of other genes. Specifically, the forkhead box G1 protein acts as a transcriptional repressor, turning off (repressing) the activity of certain genes when they are not needed. Researchers believe that this protein plays an important role in brain development, particularly in a region of the embryonic brain known as the telencephalon. The telencephalon ultimately develops into several critical structures, including the the largest part of the brain (the cerebrum), which controls most voluntary activity, language, sensory perception, learning, and memory.
Changes involving the FOXG1 gene cause FOXG1 syndrome, a rare disorder characterized by impaired development and structural brain abnormalities. This condition was previously described as a congenital variant of Rett syndrome, which is a similar disorder of early development. However, doctors and researchers have identified some important differences between the two conditions, so now FOXG1 syndrome is usually considered to be distinct from Rett syndrome.