Methionine Adenosyltransferase I/III Deficiency

Methionine adenosyltransferase I/III (MAT I/III) deficiency is an inborn error of metabolism characterized by isolated persistent hypermethioninemia in the absence of cystathionine ?-synthase deficiency, tyrosinemia type I, or liver disease. The clinical consequences of MAT I/III deficiency are highly variable. It appears that most individuals, particularly those with the R264H mutation, have elevation of plasma methionine and a relatively benign course, although the elevated methionine may be associated with an unusual breath odor. However, some patients have more severe findings including cognitive deficits, neurologic abnormalities, demyelination and other abnormalities on brain MRI

Tests Available

Forms and Documents

Test Details

  • Confirmation of biochemical diagnosis
  • Carrier testing
  • Prenatal diagnosis in at risk pregnancies
  • Capillary Sequencing Reflex to Exon Array


4-5 weeks
2-5 mL Blood - Lavender Top Tube
Oral Rinse (30-40 mL)|Buccal Swabs


  • 796.6 Abnormal findings on neonatal screening
  • 277.8 Other specified disorders of metabolism
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  7. Chamberlin et al., (2000) Am J Hum Genet 66:347-355Chamberlin et al., (2000) Am J Hum Genet 66:347-355