Another mom of two microcephalic kids with a terminal diagnosis. What were the chances, she asks? About 25% according to geneticists
This disorder is one that is tested for during the birth blood test screening. It might be rare, but its known enough to be testable for.
If its not severe enough to be found during that then its a milder form. Or we have a woo that wouldn't do testing.
The incidence of NKH is predicted to be approximately 1:76,000.
Nonketotic Hyperglycinemia
The severe classic form of NKH typically presents in the first week of life with low muscle tone, lethargy, seizures, coma, and apnea requiring ventilator support. The ventilator is typically needed for a period of 10-20 days before the apnea resolves. A portion of individuals with severe classical NKH die during the neonatal period, often due to withdrawal of intensive care supports. All children with severe classical NKH who survive the neonatal period have severe developmental delay. Most individuals do not reach milestones past those reached by the typical 6-week-old infant. Seizures gradually worsen and can be difficult to control. Feeding difficulties and orthopedic problems can occur. Airway maintenance becomes poor over time due to low muscle tone, and is often the cause of death.
Individuals with attenuated classic NKH can present in the neonatal period or later in infancy. Presentation in the neonatal period resembles that of severe classic NKH. Those who present in infancy can have low muscle tone, lethargy, and seizures. Individuals with attenuated classic NKH have variable developmental progress. Developmental delays can range from mild to profound. They can often walk and achieve various motor skills. They often have hyperactivity and behavioral problems.
The clinical picture of individuals with variant NKH is rapidly evolving. Presentation varies depending upon what gene is mutated and the specific mutation itself. Particular symptoms can include: problems with spasticity or balance, problems with the nerve of the eye (optic neuropathy), problems with the white matter of the brain, heart weakness, increased resistance to blood flow in the lungs, accumulation of acid in the blood, loss of skills that the child had achieved, or seizures. Most children have only some of these problems.
Treatment
There is no curative treatment for NKH. However, there are treatments that can improve outcomes.
Sodium benzoate is used to reduce serum glycine levels. Benzoate binds to glycine in the body to form hippurate, which is excreted in the urine. This treatment reduces seizures and improves alertness. Plasma glycine levels must be monitored closely to ensure sodium benzoate is at an effective and non-toxic level.
Dextromethorphan is commonly used to reduce seizures and improve alertness. Dextromethorphan binds to NMDA receptors in the brain. These receptors are over-stimulated in individuals with NKH due to increased glycine levels in the brain. Glutamate is the neurotransmitter that predominately binds to these receptors. Dextromethorphan binds to the NMDA receptors, blocking glutamate from binding to the receptor. Ketamine is another NMDA receptor blocker that is also used. In patients with attenuated NKH, use of dextromethorphan can help with attention and chorea, and if treated early together with benzoate, can improve development and seizures.
Seizure management in individuals with severe classic NKH is difficult and usually requires multiple anticonvulsants. Valproate is not
recommended for patients with NKH as it inhibits the residual glycine cleavage enzyme activity. Vigabatrin should rarely be used as many children with NKH have had adverse reactions to it.
IIRC, he did have a colostomy for a while, but they did make him a fully functional GI tract; however, I heard they were probably not going to have any more children because he had a cousin born with the same condition.
