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Arginase 1 Deficiency

Arginase 1 Deficiency (ARG1-D) is an inherited metabolic disorder affecting children, teens, and adults. It is characterised by high levels of plasma arginine.

ARG1-D is a type of urea cycle disorder (UCD) that impacts a person’s health over time. This rare disease affects not only the person who has been diagnosed, but also their family and loved ones. 

Understanding ARG1-D

Facts you should know 1-5

  • ARG1-D is caused by the body’s inability to break down arginine in the urea cycle
  • Arginine builds up in the body, impacting a person’s ability to do the basic tasks of everyday life
  • Symptoms usually appear between 2 and 4 years of age and continue to progress into adulthood
  • In some cases, symptoms can appear after puberty
Talk to your doctor if your child or loved one may be showing symptoms of ARG1-D
*specific signs and symptoms can vary depending on the individual
1. Carvalho DR et al. Pediatr Neurol. 2012;46:369–374. 2. Crombez EA, Cederbaum SD. Mol Genet Metab. 2005;84:243–251. 3. Sin YY et al. J Mol Med (Berl). 2015;93:1287–1296. 4. Cai X et al. Medicine. 2018;97:e9880. 5. Bakhiet M et al. Medicine (Baltimore). 2018;97:e10780.

Diagnosis and detection of ARG1-D

Early detection of ARG1-D is critical and can help patients get the treatment they need

You may need a combination of tests:

  • Newborn screening (available only in certain countries)
  • A blood test for amino acids to see if high levels of arginine are present
  • Genetic testing which can confirm an ARG1-D diagnosis

Sometimes ARG1-D can be missed or misdiagnosed as other conditions such as cerebral palsy or hereditary spastic paraplegia as the manifestations of ARG1-D often mimic those of other neurologic and neurometabolic disorders.

Managing ARG1-D

Currently, this condition is managed by restricting dietary protein intake and by adding dietary supplements and medications as prescribed by your healthcare team

Restricting diet can be a challenge for many families managing ARG1-D. Fortunately, there are people to help. Your care team may include a dietitian, who can help you plan meals and shopping trips.

ARG1-D is typically managed by a team of multiple specialists

These healthcare providers all play different roles in understanding and managing ARG1-D. Your care team may include some or all of these providers. You may also need other specialists as well.

Primary Care Provider or Paediatrician

Your primary care provider or paediatrician can help you stay on top of your overall health. They’ll keep track of treatments and medical history as you work together to best manage your ARG1-D.

Neurologist or Paediatric neurologist

A neurologist or paediatric neurologist can help manage the health of the nervous system. This may be crucial when it comes to making sure you have the best approach to managing challenges like missed developmental milestones, intellectual delay, seizures, and other neurological symptoms.

Metabolic (Genetic) Specialist

Your metabolic or genetic specialist will be the person most involved in day-to-day management. When it comes to creating a management plan, they can help. Working together with your metabolic specialist can bring you closer to your goal of slowing the progression of the disease.

Physical Therapist and/or Movement Disorder Specialist

ARG1-D can cause physical problems like stumbling or tripping, as well as muscle tightness, also called spasticity. Physical therapists and movement disorder specialists can be very important members of your care team. They can tell you which exercises and stretches are the most effective. Their main goal is to help achieve the best possible mobility for day-to-day living.


One of the main ways to manage ARG1-D is to balance nutrition, and your Dietitian will help along the way. Restricting protein and avoiding foods with arginine may not be easy, but by working together you can make a plan that works best for you and your family.


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