Elevated plasma dihydroorotate in Miller syndrome: biochemical, diagnostic and clinical implications, and treatment with uridine

Duley, John A., Henman, Michael G., Carpenter, Kevin H., Bamshad, Michael J., Marshall, George A., Ooi, Chee Y., Wilcken, Bridget and Pinner, Jason R. (2016) Elevated plasma dihydroorotate in Miller syndrome: biochemical, diagnostic and clinical implications, and treatment with uridine. Molecular Genetics and Metabolism, 119 1-2: 83-90. doi:10.1016/j.ymgme.2016.06.008

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Author Duley, John A.
Henman, Michael G.
Carpenter, Kevin H.
Bamshad, Michael J.
Marshall, George A.
Ooi, Chee Y.
Wilcken, Bridget
Pinner, Jason R.
Title Elevated plasma dihydroorotate in Miller syndrome: biochemical, diagnostic and clinical implications, and treatment with uridine
Journal name Molecular Genetics and Metabolism   Check publisher's open access policy
ISSN 1096-7192
1096-7206
Publication date 2016-06-14
Sub-type Article (original research)
DOI 10.1016/j.ymgme.2016.06.008
Open Access Status File (Author Post-print)
Volume 119
Issue 1-2
Start page 83
End page 90
Total pages 8
Place of publication Waltham, MA, United States
Publisher Academic Press
Language eng
Subject 2712 Endocrinology, Diabetes and Metabolism
1303 Biochemistry
1312 Molecular Biology
1311 Genetics
1310 Endocrinology
Abstract Background Miller syndrome (post-axial acrofacial dysostosis) arises from gene mutations for the mitochondrial enzyme dihydroorotate dehydrogenase (DHODH). Nonetheless, despite demonstrated loss of enzyme activity dihydroorotate (DHO) has not been shown to accumulate, but paradoxically urine orotate has been reported to be raised, confusing the metabolic diagnosis. Methods We analysed plasma and urine from a 4-year-old male Miller syndrome patient. DHODH mutations were determined by PCR and Sanger sequencing. Analysis of DHO and orotic acid (OA) in urine, plasma and blood-spot cards was performed using liquid chromatography-tandem mass spectrometry. In vitro stability of DHO in distilled water and control urine was assessed for up to 60 h. The patient received a 3-month trial of oral uridine for behavioural problems. Results The patient had early liver complications that are atypical of Miller syndrome. DHODH genotyping demonstrated compound-heterozygosity for frameshift and missense mutations. DHO was grossly raised in urine and plasma, and was detectable in dried spots of blood and plasma. OA was raised in urine but undetectable in plasma. DHO did not spontaneously degrade to OA. Uridine therapy did not appear to resolve behavioural problems during treatment, but it lowered plasma DHO. Conclusion This case with grossly raised plasma DHO represents the first biochemical confirmation of functional DHODH deficiency. DHO was also easily detectable in dried plasma and blood spots. We concluded that DHO oxidation to OA must occur enzymatically during renal secretion. This case resolved the biochemical conundrum in previous reports of Miller syndrome patients, and opened the possibility of rapid biochemical screening.
Formatted abstract
Background: Miller syndrome (post-axial acrofacial dysostosis) arises from gene mutations for the mitochondrial enzyme dihydroorotate dehydrogenase (DHODH). Nonetheless, despite demonstrated loss of enzyme activity dihydroorotate (DHO) has not been shown to accumulate, but paradoxically urine orotate has been reported to be raised, confusing the metabolic diagnosis.
Methods: We analysed plasma and urine from a 4-year-old male Miller syndrome patient. DHODH mutations were determined by PCR and Sanger sequencing. Analysis of DHO and orotic acid (OA) in urine, plasma and blood-spot cards was performed using liquid chromatography-tandem mass spectrometry. In vitro stability of DHO in distilled water and control urine was assessed for up to 60 h. The patient received a 3-month trial of oral uridine for behavioural problems.
Results: The patient had early liver complications that are atypical of Miller syndrome. DHODH genotyping demonstrated compound-heterozygosity for frameshift and missense mutations. DHO was grossly raised in urine and plasma, and was detectable in dried spots of blood and plasma. OA was raised in urine but undetectable in plasma. DHO did not spontaneously degrade to OA. Uridine therapy did not appear to resolve behavioural problems during treatment, but it lowered plasma DHO.
Conclusion: This case with grossly raised plasma DHO represents the first biochemical confirmation of functional DHODH deficiency. DHO was also easily detectable in dried plasma and blood spots. We concluded that DHO oxidation to OA must occur enzymatically during renal secretion. This case resolved the biochemical conundrum in previous reports of Miller syndrome patients, and opened the possibility of rapid biochemical screening.
Keyword Dihydroorotate-dehydrogenase
Miller syndrome
POADS
Mitochondria
Screening
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Mater Research Institute-UQ (MRI-UQ)
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Created: Thu, 07 Jul 2016, 21:30:21 EST by Ms Felicity Lindberg on behalf of School of Pharmacy