Welcome to the Rare Classroom, a new series from Patient Worthy. Rare Classroom is designed for the curious reader who wants to get informed on some of the rarest, most mysterious diseases and conditions. There are thousands of rare diseases out there, but only a very small number of them have viable treatments and regularly make the news. This series is an opportunity to learn the basics about some of the diseases that almost no one hears much about or that we otherwise haven’t been able to report on very often.

Eyes front and ears open. Class is now in session.

The disease that we will be learning about today is:

Arginase Deficiency Disorder

Sometimes just called arginase deficiency or argininemia.

What is Arginase Deficiency Disorder?

• Arginase deficiency disorder is a urea cycle disorder in which a deficiency of the enzyme arginase results in the abnormal accumulation of ammonia and arginine in the blood
  • The urea cycle is a chain of reactions that take place in liver cells which are responsible for processing excessive nitrogen
• This buildup, particularly of ammonia, has a toxic effect, resulting in harmful symptoms
• Diagnosis usually conducted via fetal blood sample, part of routine newborn screening
• Arginase deficiency disorder is a very rare disease, with less than 1,000 patients estimated in the US

How Do You Get It?

• Arginase deficiency disorder is a genetic disorder which is inherited in an autosomal recessive pattern.
  • This means that both parents of the patient must carry a copy of the mutated gene in order to pass along the disorder
• Mutations of the gene ARG1 are responsible for arginase deficiency disorder
• This mutation prevents the production of arginase, resulting in a disruption in the urea cycle. As a result, arginine and ammonia begin to buildup in the body

What Are the Symptoms?

• Symptoms of arginase deficiency begin early in life, typically in infancy or childhood
• The buildup of arginine and ammonia result in the following symptoms:
  • Hypotonia (low muscle tone)
  • Dehydration
  • Lethargy
  • Stunted growth
  • Developmental delays
  • Seizures
  • Microcephaly (small head size)
  • Speech problems
  • Intellectual disability

How Is It Treated?

• A number of treatments are used for arginase deficiency disorder such as:
  • Dietary changes (limiting protein intake)
  • Ondansetron hydrochloride
  • Sodium benzoate
  • Palonosetron
  • Carglumic acid
  • Sodium phenylbutyrate
  • Glycerol phenylbutyrate

Where Can I Learn More???

• Check out our cornerstone on this disease here.