ACYL-COA DEHYDROGENASE DEFICIENCY 003 1-3998/83/17 1 1-0877$02.00/0 PEDIATRIC RESEARCH Vol. 17. No. 11. 1983 Copyright 0 1983 International Pediatric Research Foundation, Inc. Primed in U.S. A. Medium-Chain Acyl-CoA Dehydrogenase Deficiency in Children with Non-Ketotic Hypoglycemia and Low Carnitine Levels CHARLES A. STANLEY,'34' DANIEL E. HALE, PAUL M. COATES, CAROLE L. HALL, BARBARA E. CORKEY, WILLIAM YANG, RICHARD I. KELLEY, ELISA L. GONZALES, JOHN R. WILLIAMSON, AND LESTER BAKER Division (?fEndocrinolog.v/Diabetes,[C.A.S., D.E.H., E.L.G., L.B.], Genetics[P.M.C.], and Metabolis~n [W. Y.,R.I.K.]ofthe Department ofPediatrics and the Department of Biochemistry and Biophysics [B.E.C.,J. W.R.], University of Penns.vlvania School of Medicine; The Children's Hospital of Philadelphia, Philadelphia, Pennsvlvunia and the School of Chemistry, Georgia Institute of Technology [C.L.H.], Atlanta, Georgia, USA Summary The oxidation of fatty acids for energy production not only plays an important rolein working skeletal and cardiac muscle, Three children in two families presented in early childhood but also is crucial for maintenance of fuel homeostasis during with episodes of illness associated with fasting which resembled periods of fasting. During fasting, the utilization of fatty acids Reye's syndrome: coma, hypoglycemia, hyperammonemia, and helps to conserve glucose for brain metabolism and the oxidation fatty liver. One child died with cerebral edema during an episode. of fatty acids to ketones in the liver yields both energy for Clinical studies revealed an absence of ketosis on fasting (plasma gluconeogenesis as well as fat-derived substrates that can be used beta-hydroxybutyrate ~0.4mmole/liter) despite elevated levels by the brain to further spare glucose consumption. In the past of free fatty acids (2.6-4.2 mmole/liter) which suggested that several years, an increasing number of inherited defects in the hepatic fatty acid oxidation was impaired. Urinary dicarboxylic pathway of fatty acid oxidation have been described. Depending acids were elevated during illness or fasting. Total carnitine levels on the degree of involvement of liver, heart, and skeletal muscle, were low in plasma (18-25 pmole/liter), liver (200-500 nmole/ the clinical features of these disorders range from recurrent g), and muscle (500-800 nmolelg); however, treatment with L- episodes of fasting coma and hypoglycemia, which may mimic carnitine failed to correct the defect in ketogenesis. Studies on Reye's syndrome, to progressive muscle weakness resembling ketone production from fatty acid substrates by liver tissue in muscular dystrophy. In some of these disorders, such as carnitine vitro showed normal rates from short-chain fatty acids, but very palmityl-transferase (2,8)and hydroxymethyl-glutaryl-CoA lyase low rates from all medium and long-chain fatty acid substrates. deficiencies (27), the site of the metabolic defect has been iden- These results suggested that the defect was in the mid-portion of tified. In others, such as type I1 glutaric aciduria (24) and the the intramitochondrial beta-oxidation pathway at the medium- dicarboxylic acidurias (I, 4, 13, 23, 3l), the site of defect has not chain acyl-CoA dehydrogenase step. A new assay for the electron yet been established. One of the disorders where the site of defect transfer flavoprotein-linked acyl-CoA dehydrogenases was used remains uncertain is a heterogeneous group associated with to test this hypothesis. This assay follows the decrease in electron deficiency of carnitine, a co-factor required for transport of long- transfer flavoprotein fluorescence as it is reduced by acyl-CoA-- chain fatty acids into mitochondria. At least two clinical syn- acyl-CoA dehydrogenase complex. Results with octanoyl-CoA as dromes appear to be associated with carnitine deficiency: a substrate indicated that patients had less than 2.5% normal systemic form (16) and a myopathic form (9). Carnitine replace- activity of medium-chain acyl-CoA dehydrogenase. The activities ment therapy has sometime? been effective (5),but frequently is of short-chain and isovaleryl acyl-CoA dehydrogenases were not (3), suggesting that the primary abnormality in many of these normal; the activity of long-chain acyl-CoA dehydrogenase was cases is not in carnitine biosynthesis (10, 11). one-third normal. The present report describes two families with a defect in fatty These results define a previously unrecognized inherited met- acid oxidation associated with low plasma and tissue carnitine abolic disorder of fatty acid oxidation due to deficiency of me- levels in which carnitine deficiency is not the cause, but instead dium-chain acyl-CoA dehydrogenase. The carnitine deficiency in may be the consequence of impaired fatty acid oxidation. The these patients appears to be a secondary consequence of their affected children in these two families presented in early child- defect in fatty acid oxidation. It is possible that other patients hood with life-threatening episodes of fasting coma and hypogly- with "systemic carnitine deficiency," who fail to respond to cemia that resembled Reye's syndrome. Clinical studies revealed carnitine therapy, may also have defects in fatty acid oxidation an absence of ketosis during fasting, which suggested that hepatic similar to medium-chain acyl-CoA dehydrogenase deficiency. fatty acid oxidation was impaired. Because there were no signs Abbreviations of muscle weakness, liver biopsies were obtained to analyze the pathway of fatty acid oxidation. These studies demonstrated a ACD, acyl-CoA dehydrogenase, defect in intramitochondrial beta-oxidation at the medium-chain BOB, beta-hydroxybutyrate acyl-CoA dehydrogenase step. A specific deficiency of this en- CPT, carnitine palmityl transferase zyme was confirmed using a new assay that was developed for CPT,, CPT activity on outer surface of mitochondria use in small samples of unfractionated tissue. Subsequent studies ETF, electron transfer flavoprotein have shown that this defect can now also be demonstrated in FFA, free fatty acid cultured skin fibroblasts (6). 878 STANLEY ET AL. PATIENTS The past medical history was femarkable only for a prior Patienr M-1. This female patient was first admitted to the unexplained episode of hypoglycemia at 6 months of age. Growth, development, and muscle strength had been normal. Children's Hospital of Philadelphia at 13 months of age because of coma. She had been the 2660 g product of a normal pregnancy Specimens of liver and skeletal muscle were obtained soon after and, except for frequent ear infections, had been well. Her growth death. Total carnitine levels in these tissues were found to be low (see "Results") and suggested the possibility of an inherited and development had also been normal. Four days before ad- mission she developed symptoms of a viral illness with low grade metabolic defect in fatty acid oxidation. fever, irritability, mild diarrhea, and intermittent vomiting. On Patient B-2. Patient B-2 is the oldest brother of patient B-1. the morning of admission she was found unarousable in bed At age 2 3/~2, he had an episode of coma and hypoglycemia after with labored breathing. She stopped breathing on the way to sleeping late one morning. He cried out and was found unre- another hospital and was given mouth-to-mouth ventilation. In sponsive by his parents. He was taken to an emergency room where he was noted to be staring and unresponsive with arms the emergency room she had a generalized seizure and received a large dose of diazepam. She was stabilized and transported to and legs stiffly flexed. Laboratory studies showed plasma glucose, 8 mg/dl (0.44 mmole/liter); normal serum sodium, potassium the Children's Hospital of Philadelphia. On arrival she was and chloride; serum bicarbonate, 19 mmole/liter; and moderate obtunded, responded only to painful stimuli, and required me- ketonuria. He was transferred to Children's Hospital of Phila- chanical ventilation. Physical examination was normal; the liver was not enlarged. Laboratory studies showed a spinal fluid glu- delphia where additional laboratory tests showed an elevated blood ammonia (185 pg/dl; 109 pmole/liter) compared to a cose of 23 mg/dl (1.3 mmole/liter); normal serum sodium, control (1 50 &dl; 88 pmole/liter), slightly elevated transaminase potassium, and chloride; bicarbonate, 11 mmole/liter; urea ni- (64 U/ml; 0.5 pmol .s-'/liter-'), and normal prothrombin time. trogen, 14 mg/dl (5.0 mmole/liter); blood ammonia, 52 pgldl The liver was not enlarged. He had several seizures after treat- (30 pmole/liter); hemoglobin, 12.3 g/dl (7.7 mmole/liter); and ment was started with intravenous fluids. He improved slowly white blood count, 21,700/mm3 (2 1.7 x 109/liter); and a small over 3 days. One week later, he tolerated a fast of 36 h without amount of ketones in the urine. She was treated with intravenous developing hypoglycemia (lowest plasma glucose, 58 mg/dl; 3.2 dextrose and fluids and began to improve slowly. On the third day, when the intravenous fluids were stopped and nasogastric mmole/liter) or symptoms. Because the episode of coma had feedings were begun she became obtunded again and had a occurred after a longer period of overnight fasting than was usual for him, the parents were advised to avoid letting him fast more cardiorespiratory arrest. At this time the liver was noted to be firm and enlarged to 4 cm below the costal margin. The plasma than 12 h. He has had no further episodes of coma. At age 10 glucose was 34 mg/dl (I .9 mmole/liter); serum bicarbonate, 16 years, he appears physically and developmentally normal and has no signs of muscle weakness. His total plasma carnitine level mmole/liter; and blood ammonia, 138 &dl (8 1 pmole/liter). A urine specimen at the time of this episode showed very elevated is low (25 pmole/liter).