Propionic acidemia

Propionic acidemia is a rare organic acidemia caused by a deficiency in the enzyme propionyl coenzyme A carboxylase. 

Epidemiology

Propionic acidemia has an incidence of around 1 in 150,000 in the general population ¹.  

Clinical presentation

Around 80% of children with propionic acidemia will present within 3 months of birth with symptoms becoming evident during an episode of metabolic decompensation. These include ^1,2:

• poor feeding

• vomiting

• lethargy

• coma

Symptoms are due to the metabolic derangement caused by the acidemia with severe ketoacidosis and hyperammonemia being present ².

Chronic and intermittent forms of the disease have also been described ².

Pathology

The disease is due to a deficiency in propionyl coenzyme-A (CoA) carboxylase and is inherited in an autosomal recessive pattern. Propionyl CoA carboxylase converts propionyl CoA to methylmalonyl CoA and is involved in the metabolism of several amino acids (e.g. valine and leucine) and odd-numbered chained fatty acids ². Deficiency of this enzyme results in an accumulation of propionic acid. 

Markers

Elevated levels of propionylcarnitine on a newborn screening test is present ⁵.

Radiographic features

Plain radiograph

Cardiomyopathy may be a feature of chronic propionic acidemia so cardiomegaly may be apparent ¹.

MRI

The imaging signs in propionic acidemia are non-specific ².

• T2/FLAIR

  • in neonates

    • diffuse edema and signal irregularities in the cerebral white matter

    • with sparing of the basal ganglia ²

  • in older children

    • hyperintense lesions in basal ganglia (mainly in the putamen and caudate)

    • abnormal signal intensity and edema in the cerebral and cerebellar cortices are less common ²

• DWI: in both neonates and older children areas of restricted diffusion in affected regions ²

• MR spectroscopy

  • typical pattern during acute decompensation may include ^2,4:

    • NAA level: decreased

    • glutamate level: decreased

    • glutamine level: decreased

    • lactate level: increased

During the chronic untreated form of the disease, abnormal myelination as well as cortical and white matter atrophy can be expected ².

Treatment and prognosis

Long-term treatment of propionic acidemia is a low protein diet (especially low in the offending amino acids; e.g. valine) to reduce the formation of propionic acid in the body ¹. Liver transplantation may be required in some cases where despite dietary modification recurrent episodes of metabolic decompensation still occur ⁵.