Genetics of Methylmalonic Acidemia Follow-up

Updated: Mar 16, 2015
  • Author: Brendan Lee, MD, PhD; Chief Editor: Maria Descartes, MD  more...
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Follow-up

Further Outpatient Care

Depending on age and metabolic control, follow up in regular intervals (eg, 1-4 follow-up visits or more per year) with a biochemical geneticist familiar with the management of methylmalonic acidemia (MMA).

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Inpatient & Outpatient Medications

L-carnitine

L-carnitine (100-300 mg/kg orally [PO], divided 3 times daily [tid])

Hydroxocobalamin/cyanocobalamin

Hydroxocobalamin is by far more effective than cyanocobalamin. Administer hydroxocobalamin (1 mg/d intramuscularly [IM]) only to patients with cobalamin-responsive forms of MMA.

Metronidazole

Administer metronidazole (10-20 mg/kg PO divided tid) or neomycin (50 mg/kg PO, divided tid) to reduce gut propionate production. Administer a limited trial with metronidazole (1-2 mo).

Betaine

Children younger than 3 years require 100 mg/kg PO divided twice daily (bid).

Children older than 3 years require 250 mg/kg PO divided bid.

Adults require 250 mg/kg PO divided bid.

Some patients require amounts up to 20 g/d. Consider this dosage as nonspecific therapy for patients with combined MMA and homocystinuria to reduce plasma homocysteine levels.

Folate

Infants require 15 mcg/kg/d or 50 mcg/d.

Children require 1 mg/d initial dose, then 0.1-0.3 mg/d.

Adults require 1 mg/d initial dose, then 0.5 mg/d (for patients with combined MMA and homocystinuria to reduce plasma homocysteine levels).

Carglumic acid (N-carbamyl glutamate)

Children and adults need 100-250 mg/kg/d titrated to control ammonia as needed.

Some patients may not need this treatment or may need lower dosing.

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Transfer

Treat children with MMA only at tertiary care facilities that have access to a multidisciplinary team of biochemical geneticists, dietitians, neonatologists, and other medical specialists.

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Prognosis

Prognosis depends on the type of MMA and whether the patient's condition is well controlled (ie, in general and during episodes of metabolic decompensation).

More severe cases are at risk for secondary complications, though each of these are incompletely penetrant, as follows:

  • Developmental delay with neurological dysfunction due to metabolic stroke affecting the basal ganglia, movement disorder, and white matter changes

  • Progressive renal dysfunction with tubulointerstitial nephritis

  • Pancreatitis, which can be recurrent and/or chronic

  • Susceptibility to infection, including Gram-negative organisms

  • Optic atrophy

  • Growth failure

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Patient Education

Educate caregivers about how to identify and respond to episodes of metabolic decompensation in patients with MMA. Supply a written emergency regimen and card.

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