HHH syndrome

HHH Syndrome (Hyperornithinemia-Hyperammonemia-Homocitrullinuria Syndrome) is a rare autosomal recessive metabolic disorder characterized by an inability to properly process the amino acid ornithine. The syndrome was first described in 1969 by three Canadian researchers, Hayasaka, Harper, and Haworth, from whom the syndrome gets its name.

Symptoms and Signs

The symptoms of HHH syndrome can vary widely among affected individuals. They typically include neurological problems such as developmental delay, intellectual disability, seizures, ataxia (lack of muscle control), and hyperreflexia (overactive reflexes). Other symptoms can include hepatomegaly (enlarged liver), coagulopathy (blood clotting disorder), and pulmonary symptoms such as hyperventilation.

Causes

HHH syndrome is caused by mutations in the SLC25A15 gene, which provides instructions for making a protein that is primarily found in the liver and kidneys. This protein is involved in the urea cycle, a series of reactions that occur in liver cells. The urea cycle processes excess nitrogen, generated when protein is used by the body, to make a compound called urea that is excreted in the urine.

Diagnosis

Diagnosis of HHH syndrome is based on the presence of characteristic symptoms, a detailed patient history, a thorough clinical evaluation, and a variety of specialized tests. These tests can include blood tests, urine tests, and genetic testing.

Treatment

Treatment of HHH syndrome is aimed at managing the symptoms and preventing complications. This can include a low-protein diet, medications to reduce the level of ammonia in the blood, and in some cases, liver transplantation.

Prognosis

The prognosis for individuals with HHH syndrome varies. Some individuals have a normal lifespan with treatment, while others may have severe neurological impairment and life-threatening metabolic crises.

See Also

• Urea cycle disorder
• Metabolic disorder
• Ornithine translocase deficiency

HHH syndrome Resources
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