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Letters |
1 Clinical Chemistry Department, West Midlands Regional Laboratory for Neonatal Screening and Inherited Metabolic Disorders, Diana, Princess of Wales, Childrens Hospital, Steelhouse Lane, Birmingham B4 6NH, United Kingdom
aAuthor for correspondence. E-mail anne.green{at}bhamchildrens.wmids.nhs.uk.
To the Editor:
We were interested by the paper of Chace et al. (1) and the accompanying editorial (2) on the postmortem diagnosis of organic acid and fatty acid defects by analysis of acyl carnitines in dried-blood-spot specimens and fully support the need for metabolic investigations in this situation.
The group reports 66 presumptive or confirmed diagnoses from a total of 7058 postmortem specimens (0.9%). The major diagnoses were fatty acid oxidation defects, particularly medium-chain acyl CoA dehydrogenase deficiency. In some cases, the diagnosis remained presumptive because confirmatory tests were not available.
We have experience, albeit limited, in the investigation of all cases of sudden unexplained death in infants (SUDI) <2 years of age in the City of Birmingham, United Kingdom. Our protocol includes plasma and blood-spot acyl carnitines and amino acids, urine organic acids, and the collection of a skin biopsy, which is stored frozen pending preliminary results. Over a 2.5-year period, we have investigated 58 cases. Definitive diagnosis was established in three cases (5% total). The diagnoses made were long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (confirmed by mutation analysis), carnitine transporter defect (confirmed by cultured fibroblast fatty acid oxidation), and citrullinemia (confirmed by cultured fibroblast citrulline incorporation). Seven additional cases had acyl carnitine analyses that suggested the possibility of a fatty acid defect (see Table 1
). The frozen skin biopsies from these patients were subsequently cultured for fatty acid oxidation studies (3), which were normal.
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These findings illustrate the importance of collecting a skin biopsy as well as blood to enable a definitive diagnosis. The biopsy can be frozen at the time of collection and then cultured only if required (4). In the United Kingdom we feel that this is a practical approach for the investigation of all cases of SUDI <2 years of age.
The ability to make a definitive diagnosis is important for genetic counseling and enabling the possibility of prenatal diagnosis; we would like to emphasize that a skin biopsy be routine as part of a protocol for investigation for metabolic disease in SUDI.
References
The following articles in journals at HighWire Press have cited this article:
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M. R. Murali, A. Kratz, and K. E. Finberg Case 40-2006 -- A 64-Year-Old Man with Anemia and a Low Level of HDL Cholesterol N. Engl. J. Med., December 28, 2006; 355(26): 2772 - 2779. [Full Text] [PDF] |
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D. Sun, M. G. Cree, X.-j. Zhang, E. Boersheim, and R. R. Wolfe Measurement of stable isotopic enrichment and concentration of long-chain fatty acyl-carnitines in tissue by HPLC-MS J. Lipid Res., February 1, 2006; 47(2): 431 - 439. [Abstract] [Full Text] [PDF] |
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C M Loughrey, M A Preece, and A Green Sudden unexpected death in infancy (SUDI) J. Clin. Pathol., January 1, 2005; 58(1): 20 - 21. [Full Text] [PDF] |
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