What is Non-ketotic Hyperglycinemia (NKH)?
Non-Ketotic Hyperglycinemia, NKH for short, is a rare genetic disorder that affects 1 in every 60,000 infants born. Children with this condition have a problem breaking down the amino acid glycine. This is caused by a defect in the genetic code for the machinery that is responsible for the glycine breakdown (called glycine cleavage enzyme). Amino acids are natural components of our body. Because glycine is not broken down, it accumulates in the body. Glycine is an important molecule in the brain where it has various functions such as transmitting signals from one brain cell to another. Excessive glycine disrupts the function of the brain.
Children with NKH usually present as newborns, but 1 in 5 children presents in infancy. Typical symptoms include seizures, low tone, and severe problems with learning and development. This can profoundly affect a child’s ability to learn and to do normal things such as eating, sitting, and walking. The seizures can be so severe that they are hardly controlled despite the use of several medications for seizures. Not all children are equally affected. Most commonly children are severely affected and do not make developmental progress and have difficult to control seizures. Some children, about 1 in 6, are more mildly affected. They make progress in their development, and have seizures that can be controlled more easily. Current treatment is limited.