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Nonketotic Hyperglycinemia

Have you heard of Nonketotic Hyperglycinemia? Do you know what it is? Here at Forward Facing we feel it is important for us to share some rare disorders and conditions that some of us will not have heard of. Below we wanted to give you a brief overview of the disorder. All information is from NKH International Family Network.

What is Nonketotic Hyperglycinemia?

Nonketotic Hyperglycinemia is a genetic metabolic disorder which prevents the body from processing glycine. Nonketotic Hyperglycinemia (NKH) is also known as Glycine Encephalopathy.

Nonketotic hyperglycinemia, NKH for short, is a rare genetic disorder that affects 1 child in every 60,000 born. Children with this condition have a problem breaking down the amino acid glycine.

Because glycine is not broken down, it accumulates in the body. Glycine is an important molecule in the brain and has various functions, such as transmitting signals from one brain cell to another. Toxic levels glycine disrupts the function of the brain causing brain damage.

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. Unfortunately, most born with NKH have limited life spans.

What is Glycine, and what is it used for?

Glycine is an amino acid, the smallest amino acid there is. Known as the building blocks of life, amino acids are what makeup proteins and are crucial for almost every cell function in the body.

Glycine acts as a neurotransmitter, chemical signals found in the brain and central nervous system that runs throughout the body. It can also reduce activity in the spinal cord and brain stem while increasing activity in the brain cortex. This affects cognitive function, learning and retaining information. As a neurotransmitter, it is also vital in ensuring messages are transmitted correctly from the brain to other parts of the body.

Glycine is processed through the Glycine Cleavage System (GCS), which takes Glycine and creates ammonia and carbon dioxide.

What causes Nonketotic Hyperglycinemia?

NKH is a genetic disorder. There are several genes which tell the body how to process glycine, via the Glycine Cleavage System. With NKH, there is a mutation of genes which prevent the GCS from operating correctly, leading to the increase of glycine levels in the body.

To inherit the mutation, both parents carry one copy of the mutated gene. The child has inherited two copies of the mutated gene – one from each parent. Read more about genetics here.

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