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Adenosine Kinase Deficiency Disrupts the Methionine Cycle and Causes Hypermethioninemia, Encephalopathy, and Abnormal Liver Function
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2011 (English)In: American Journal of Human Genetics, ISSN 0002-9297, E-ISSN 1537-6605, Vol. 89, no 4, 507-515 p.Article in journal (Refereed) Published
Abstract [en]

Four inborn errors of metabolism (IEMs) are known to cause hypermethioninemia by directly interfering with the methionine cycle. Hypermethioninemia is occasionally discovered incidentally, but it is often disregarded as an unspecific finding, particularly if liver disease is involved. In many individuals the hypermethioninemia resolves without further deterioration, but it can also represent an early sign of a severe, progressive neurodevelopmental disorder. Further investigation of unclear hypermethioninemia is therefore important. We studied two siblings affected by severe developmental delay and liver dysfunction. Biochemical analysis revealed increased plasma levels of methionine, S-adenosylmethionine (Ado Met), and S-adenosylhomocysteine (AdoHcy) but normal or mildly elevated homocysteine (Hcy) levels, indicating a block in the methionine cycle. We excluded S-adenosylhomocysteine hydrolase (SAHH) deficiency, which causes a similar biochemical phenotype, by using genetic and biochemical techniques and hypothesized that there was a functional block in the SAHH enzyme as a result of a recessive mutation in a different gene. Using exome sequencing, we identified a homozygous c.902C>A (p.Ala301Glu) missense mutation in the adenosine kinase gene (ADK), the function of which fits perfectly with this hypothesis. Increased urinary adenosine excretion confirmed ADK deficiency in the siblings. Four additional individuals from two unrelated families with a similar presentation were identified and shown to have a homozygous c.653A>C (p.Asp218Ala) and c.38G>A (p.Gly13Glu) mutation, respectively, in the same gene. All three missense mutations were deleterious, as shown by activity measurements on recombinant enzymes. ADK deficiency is a previously undescribed, severe IEM shedding light on a functional link between the methionine cycle and adenosine metabolism.

Place, publisher, year, edition, pages
2011. Vol. 89, no 4, 507-515 p.
Keyword [en]
s-adenosylhomocysteine hydrolase, enzymatic defect, mammalian-cells, homocysteine, metabolism
National Category
Genetics
Identifiers
URN: urn:nbn:se:kth:diva-46846DOI: 10.1016/j.ajhg.2011.09.004ISI: 000295951300005Scopus ID: 2-s2.0-80053927702OAI: oai:DiVA.org:kth-46846DiVA: diva2:454379
Funder
Swedish Research CouncilScience for Life Laboratory - a national resource center for high-throughput molecular bioscience
Note
QC 20111107Available from: 2011-11-07 Created: 2011-11-07 Last updated: 2017-12-08Bibliographically approved

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