What is the Difference Between Type I and Type 2 Citrullinemia

The key difference between type I and type 2 citrullinemia is that type I citrullinemia is caused due to a mutation in the ASS gene, while type 2 citrullinemia caused due to a mutation in the SLC25A13 gene.

Citrullinemia is an autosomal recessive urea cycle disorder. This disorder causes ammonia and other toxic substances to accumulate in the blood. The urea cycle is a sequence of chemical reactions that occur in the liver. These biochemical reactions process excess nitrogen that is generated when protein is used for energy by the human body. The reactions in this cycle ultimately make urea, which excretes through the kidneys. The problems in this cycle lead to citrullinemia. Citrullinemia is of two types: type I and type II. Both forms have different signs and symptoms and are caused by different gene mutations.

CONTENTS

1. Overview and Key Difference
2. What is Type I Citrullinemia
3. What is Type 2 Citrullinemia
4. Similarities – Type I and Type 2 Citrullinemia
5. Type I vs Type 2 Citrullinemia  in Tabular Form
6. Summary – Type I and Type 2 Citrullinemia

What is Type I Citrullinemia?

Type I citrullinemia is a type of citrullinemia that is caused by a mutation in the ASS gene. This disease is also called arginosuccinate synthetase deficiency. This is due to the ASS gene mutation, which causes a deficiency in an important enzyme called arginosuccinate synthetase that is involved in the urea cycle. This enzyme plays a key role in excreting excess nitrogen from the human body. When this enzyme is deficient fully or partially, the ammonia builds up in the blood and causes the signs and symptoms of type I citrullinemia.

Figure 01: Urea Cycle

The signs and symptoms of type I citrullinemia are excessive vomiting, anorexia, refusing to eat, irritability, increasing intracranial pressure, lethargy, seizures, hypotonia, respiratory distress syndrome, hepatomegaly, cerebral edema, developmental delays, cognitive problems, cerebral palsy, hypertonia, spasticity, and liver failure. The signs and symptoms usually start from childhood.

Moreover, type I citrullinemia is diagnosed through medical history, physical examination, blood tests, and genetic tests. Furthermore, treatment options for type I citrullinemia may include a low-protein, high-calorie diet with amino acid supplements, medications like biphenyl and ammonul, intravenous arginine, sodium benzoate, sodium phenylacetate and L carnitine, and liver transplantation.

What is Type 2 Citrullinemia?

Type 2 citrullinemia is a type of citrullinemia caused due to a mutation in the SLC25A13 gene. This mutation prevents the production of functional citrin. This leads to a build-up of ammonia and other toxic substances that are responsible for the signs and symptoms of type 2 citrullinemia. The signs and symptoms of this condition usually start in adulthood. The signs and symptoms include confusion, abnormal behaviours like aggression, irritability and hyperactivity, seizures, coma, and liver disorders.

Type 2 citrullinemia can be diagnosed through medical history, physical examination, blood test, brain scan, and genetic test. Furthermore, treatment options for type 2 citrullinemia include a low-protein diet, arginine, sodium benzoate, and sodium phenylacetate to remove ammonia from the blood, dialysis, and liver transplantation.

What are the Similarities Between Type I and Type 2 Citrullinemia?

• Type I and Type 2 citrullinemia are two types of citrullinemia disorder.
• Both types are inherited in an autosomal recessive pattern.
• They lead to the build-up of ammonia and other toxic substances in the blood.
• Both can be diagnosed through blood tests and genetic tests.
• They are treated through dietary changes and liver transplantation.

What is the Difference Between Type I and Type 2 Citrullinemia?

Type I citrullinemia is caused due to a mutation in the ASS gene, while type 2 citrullinemia caused due to a mutation in the SLC25A13 gene. Thus, this is the key difference between type I and type 2 citrullinemia. Furthermore, the signs and symptoms of type I citrullinemia usually start in childhood the signs while symptoms of type 2 citrullinemia usually start in adulthood.

The below infographic presents the differences between type I and type 2 citrullinemia in tabular form for side-by-side comparison.

Summary – Type I vs Type 2 Citrullinemia

Type I and Type 2 citrullinemia are two different types of citrullinemia disorder. Both these types are inherited conditions that show an autosomal recessive pattern. They are characterized by the building up of ammonia and other toxic substances in the blood. However, type I citrullinemia occurs due to a mutation in the ASS gene, while type 2 citrullinemia occurs due to a mutation in the SLC25A13 gene. So, this is the key difference between type I and type 2 citrullinemia.

Reference:

1. “Women’s Health: Myriad Genetics.” Myriad Women’s Health, 24 June 2022.
2. “Citrullinemia Type II.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Urea cycle 1” (CC BY-SA 3.0) via Commons Wikimedia

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