Hyperglycinemia refers to abnormally high levels of a molecule, glycine.
The word nonketotic distinguishes NKH from certain other health conditions that can cause increasedglycine.
The condition is also sometimes called “glycine encephalopathy,” meaning a disease that damages the brain.
Verywell/Emily Roberts
NKH belongs to a larger group of medical conditions called inborn errors of metabolism.
These are genetic defects that lead to problems making certain chemical conversions in the body.
Symptoms
People with NKH can have variable intensity and degree of symptoms.
Most commonly, symptoms begin soon after birth.
For example, these might include severe developmental disability or seizures that are very difficult to treat.
Less commonly, people may suffer from an atypical form of the disease.
In some of these atypical cases, the disease is milder.
For example, the individual might have intellectual disability, but not nearly as severely.
These people may appear normal but then develop symptoms that affect primarily the nervous system.
Extremely rarely, infants experience something called transient NKH."
Some experts consider this a controversial diagnosis.
These infants may experience temporary symptoms that completely go away by the age of two months.
In other cases, individuals with transient NKH go on to experience some long-term problems, like intellectual disability.
Researchers arent sure how to explain this very uncommon form of the disease.
Causes
The symptoms of NKH result from abnormally high levels of glycine, a small molecule.
Glycine is a normal amino acid, one of the components used to make proteins in your body.
Glycine performs many important physiological roles.
However, if levels of glycine become too high, it can lead to problems.
Overstimulation of glycine receptors and the death of neurons can lead to some of the symptoms of the condition.
Normally, glycine is broken down by an enzyme before levels build up too high.
When there is a problem with this enzyme (called the glycine cleavage system), NKH can result.
This is brought on by abnormalgenetic mutationsin one of the proteins used to make the enzyme.
Diagnosis
Diagnosis of NKH can be challenging.
A physical exam and one’s medical history play an important role in the diagnosis.
Healthcare providers also need to rule out the possibility of medical conditions that can cause similar symptoms.
A wide variety of syndromes can cause problems like seizures in infants, including many different genetic problems.
Testing plays an important role in diagnosis.
Some of the key tests check for elevated levels of glycine.
This might include tests of glycine in the blood, urine, orcerebrospinal fluid.
However, certain medical conditions can mimic some of the laboratory findings of NKH.
These include other rare disorders of metabolism, includingpropionic acidemiaandmethylmalonic acidemia.
Less commonly, a liver biopsy might also be needed to confirm the diagnosis.
As part of the diagnosis, its also important to assess how much damage has been done from NKH.
For example, this might require tests like MRI of the brain or anEEG.
Its also important to have specialists perform neurological and developmental assessments.
Here they can receive high levels of intervention and care.
Unfortunately, there is no real treatment for the more common and severe forms of NKH.
However, for people with less severe disease, there are some treatments that may help somewhat.
These are most likely to provide some benefit if they are given early and aggressively.
These include:
Its also important to treatseizuresin NKH.
These can be very difficult to address with standard medications such as phenytoin or phenobarbital.
Successful treatment may require a combination of antiepileptic medications.
Sometimes other interventions may be needed to help control seizures, like vagal nerve stimulators or special diets.
Treatment for Other Symptoms
Other symptoms of NKH also need to be addressed.
These might include:
Its also worth investigating the possibility of clinical trials.
Inheritance
NKH is an autosomal recessive genetic condition.
That means a person with NKH has to receive an affected gene from both their mother and their father.
People with only one affected gene do not get the condition.
There is a 50 percent chance that their child would be a carrier for NKH without having symptoms.
Much less commonly, NKH can arise from a sporadic mutation.
Working with a genetic counselor is often very helpful if someone in your family was born with NKH.
This professional can give you a sense of the risks in your particular situation.
Prenatal testing is also available if there is a risk of NKH.
In vitro fertilization may also be an option for couples who want to pre-screen embryos for the disease.
A Word From Verywell
A diagnosis of NKH is a devastating one for families.
Networking with other families can be a powerful way to get information and a sense of connection.
Know that your healthcare team is here to support you in whatever way is possible.
Dont hesitate to reach out to your support system whenever you should probably.
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Van Hove JLK, Coughlin C II, Swanson M, et al.Nonketotic hyperglycinemia.
In: Adam MP, Ardinger HH, Pagon RA, et al., editors.
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