Potential Misdiagnosis of 3-Methylcrotonyl-Coenzyme A Carboxylase Deficiency Associated With Absent or Trace Urinary 3-Methylcrotonylglycine
2007
We report 2 patients with isolated 3-methylcrotonyl-coenzyme A carboxylase deficiency whose urine was devoid of, or contained only trace, 3-methylcrotonylglycine, the pathognomonic marker for this disorder. The first patient, a girl with trisomy 21, was detected through newborn screening with an elevated 5 carbon hydroxycarnitine species level, and the second patient came to clinical attention at the age of 5 months because of failure to thrive and developmental delay. Investigation of urinary organic acids revealed an elevated 3-hydroxyisovaleric acid level but no demonstrable 3-methylcrotonylglycine in both patients. Enzyme studies in cultured fibroblasts confirmed isolated 3-methylcrotonyl-coenzyme A carboxylase deficiency with residual activities of 5% to 7% and 12% of the median control value, respectively. Incorporation of 14C-isovaleric acid into intact fibroblasts was essentially normal, showing that the overall pathway was at least partially functional and potentially explaining the absence of 3-methylcrotonylglycine in urine. Mutation analysis of the MCCA and MCCB genes revealed that both patients were compound heterozygous for a missense mutation, MCCB-c.1015G→A (p.V339M), and a second mutation that leads to undetectable MCCB messenger (poly A+) RNA. Absent or trace 3-methylcrotonylglycine levels in urine raises the potential for misdiagnosis in the clinical biochemical genetics laboratory based solely on urine organic acid analysis using combined gas chromatography-mass spectrometry.
Keywords:
- Intensive care medicine
- 3-Methylcrotonylglycinuria
- Missense mutation
- Failure to thrive
- Newborn screening
- Urinary system
- 3-hydroxyisovaleric acid
- Methylcrotonyl-coenzyme A carboxylase deficiency
- Medicine
- 3-Methylcrotonylglycine
- Internal medicine
- Endocrinology
- Trisomy
- Urine organic acids
- Compound heterozygosity
- Urine
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
21
References
17
Citations
NaN
KQI