A child with acute pancreatitis and recurrent hypoglycemia due to 3-hydroxy-3-methylglutaryl-CoA lyase deficiency

Pancreatic involvement in patients with inborn errors of metabolism

Background

Repeated inflammation of the pancreas can cause pancreatitis or diabetes. It is well recognized that the organic acidemias may be complicated by pancreatitis but less recognized are other metabolic disorders in which pancreatitis can occur. This study shows that long-term follow-up of patients with various metabolic disorders in Korea revealed several with episodes of isolated pancreatitis or diabetes concomitantly with pancreatitis.

Results and discussion

In this study, two patients with methylmalonic aciduria (MMA), two with propionic acidemia (PPA), one with fatty acid oxidation disorder (FAOD), and one with hyperornithinemia, gyrate atrophy, and juvenile onset diabetes mellitus (DM) were clinically followed for up to 10 – 21 years. Two Korean siblings with MMA showed recurrent pancreatitis from the age of 15 and 19, respectively. The frequency of admission due to pancreatitis was up to 11 times. One patient with MMA developed diabetes mellitus at the age of 20. The other patient with MMA developed recurrent pancreatitis at 4 years and diabetes at 8 years of age. One of the patients with PPA presented with diabetic ketoacidosis. The other PPA patient died of cardiac arrest at age 10. The patient with FAOD presented with pancreatitis at 10 years and died at the age of 15 years due to cardiac arrest. A 35-year-old woman with hyperornithinemia/gyrate atrophy was diagnosed with juvenile onset diabetes at the age of 7 years. No pancreatitis occurred during the follow-up period.

Conclusions

We conclude that various metabolic disorders can trigger acute or chronic pancreatitis. Proper and prompt multidisciplinary management of metabolic derangement is crucial for preventing pancreatic damage. Further clinical and investigational studies are required to elucidate the pathogenesis of pancreatitis and diabetes mellitus in patients with inborn errors in metabolism.

Hepatic Manifestations of 3-Hydroxy-3-Methylglutaryl-Coenzyme-A Lyase Deficiency in Saudi Patients: Experience of a Tertiary Care Center

3-Hydroxy-3-methylglutaryl-coenzyme-A lyase (HMGCL) deficiency, a rare autosomal recessive disorder, is caused by a homozygous or compound heterozygous mutation in the HMGCL gene (chromosome 1p36.11). HMGCL catalyzes the final step of leucine degradation and plays a key role in ketone body formation. Several studies have reported general hepatic findings (e.g., hepatomegaly) in patients with HMGCL deficiency, but currently, there are no available data regarding the incidence and epidemiology of liver involvement. The main objective of our study was to investigate the overall clinical manifestations, laboratory findings, genotype, and presence of hepatic involvement in Saudi patients with HMGCL deficiency. A retrospective chart review of patients with HMGCL deficiency including those with a documented hepatic manifestation was performed at the King Faisal Specialist Hospital & Research Centre in Riyadh, Saudi Arabia. We evaluated 50 cases of HMGCL deficiency. Hepatic findings were found in 17 patients at the time of diagnosis. The mean age of hepatic presentation was 135 days, and the median age was 56 days (range: 2-315 days). Hepatomegaly was found in 65%, abnormal biochemical profile in 47%, and an abnormal imaging in 53% of patients. The most frequent mutation in this cohort was the p.Arg41Gln founder mutation (59%). In comparison to data from the current literature, HMGCL deficiency can be considered as a diagnostic metabolite for hepatic manifestations and requires appropriate evaluation, including molecular genetic analysis.

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: Clinical presentation and outcome in a series of 37 patients

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is a rare inborn error of ketone body synthesis and leucine degradation, caused by mutations in the HMGCL gene. In order to obtain a comprehensive view on this disease, we have collected clinical and biochemical data as well as information on HMGCL mutations of 37 patients (35 families) from metabolic centers in Belgium, Germany, The Netherlands, Switzerland, and Turkey. All patients were symptomatic at some stage with 94% presenting with an acute metabolic decompensation. In 50% of the patients, the disorder manifested neonatally, mostly within the first days of life. Only 8% of patients presented after one year of age. Six patients died prior to data collection. Long-term neurological complications were common. Half of the patients had a normal cognitive development while the remainder showed psychomotor deficits. We identified seven novel HMGCL mutations. In agreement with previous reports, no clear genotype-phenotype correlation could be found. This is the largest cohort of HMGCLD patients reported so far, demonstrating that HMGCLD is a potentially life-threatening disease with variable clinical outcome. Our findings suggest that the clinical course of HMGCLD cannot be predicted accurately from HMGCL genotype. The overall outcome in HMGCLD appears limited, thus rendering early diagnosis and strict avoidance of metabolic crises important.

Induction of a Proinflammatory Response in Cortical Astrocytes by the Major Metabolites Accumulating in HMG-CoA Lyase Deficiency: the Role of ERK Signaling Pathway in Cytokine Release

3-Hydroxy-3-methylglutaric aciduria (HMGA) is an inherited metabolic disorder caused by 3-hydroxy-3-methylglutaryl-CoA lyase deficiency. It is biochemically characterized by predominant tissue accumulation and high urinary excretion of 3-hydroxy-3-methylglutarate (HMG) and 3-methylglutarate (MGA). Affected patients commonly present acute symptoms during metabolic decompensation, including vomiting, seizures, and lethargy/coma accompanied by metabolic acidosis and hypoketotic hypoglycemia. Although neurological manifestations are common, the pathogenesis of brain injury in this disease is poorly known. Astrocytes are important for neuronal protection and are susceptible to damage by neurotoxins. In the present study, we investigated the effects of HMG and MGA on important parameters of redox homeostasis and cytokine production in cortical cultured astrocytes. The role of the metabolites on astrocyte mitochondrial function (thiazolyl blue tetrazolium bromide (MTT) reduction) and viability (propidium iodide incorporation) was also studied. Both organic acids decreased astrocytic mitochondrial function and the concentrations of reduced glutathione without altering cell viability. In contrast, they increased reactive species formation (2'-7'-dichlorofluorescein diacetate (DCFHDA) oxidation), as well as IL-1β, IL-6, and TNF α release through the ERK signaling pathway. Taken together, the data indicate that the principal compounds accumulating in HMGA induce a proinflammatory response in cultured astrocytes that may possibly be involved in the neuropathology of this disease.

Chronic pancreatitis in branched-chain organic acidurias--a case of methylmalonic aciduria and an overview of the literature

A severe rare complication in patients with branched-chain organic acidurias (BCOA) is pancreatitis with a limited number of patients published so far. Here, we report on a patient with methylmalonic aciduria (MMA) who developed chronic pancreatitis after several episodes of acute pancreatitis. In addition, an overview is given about some previous published cases with BCOA who developed pancreatitis in the course of the disease. In half of the published MMA patients with pancreatitis, an acute pancreatitis was reported while the rest suffered from a chronic form of this disease. Acute pancreatitis in BCOA patients can clinically present in the context of recurrent vomiting and an impaired general physical condition even without typical signs of pancreatitis. Any form of pancreatitis should be ruled out in the assessment of acutely ill patients with BCOA.

Differential HMG-CoA lyase expression in human tissues provides clues about 3-hydroxy-3-methylglutaric aciduria

3-Hydroxy-3-methylglutaric aciduria is a rare human autosomal recessive disorder caused by deficiency of 3-hydroxy-3-methylglutaryl CoA lyase (HL). This mitochondrial enzyme catalyzes the common final step of leucine degradation and ketogenesis. Acute symptoms include vomiting, seizures and lethargy, accompanied by metabolic acidosis and hypoketotic hypoglycaemia. Such organs as the liver, brain, pancreas, and heart can also be involved. However, the pathophysiology of this disease is only partially understood. We measured mRNA levels, protein expression and enzyme activity of human HMG-CoA lyase from liver, kidney, pancreas, testis, heart, skeletal muscle, and brain. Surprisingly, the pancreas is, after the liver, the tissue with most HL activity. However, in heart and adult brain, HL activity was not detected in the mitochondrial fraction. These findings contribute to our understanding of the enzyme function and the consequences of its deficiency and suggest the need for assessment of pancreatic damage in these patients.

Incidence of 3-hydroxy-3-methylglutaryl-coenzyme A lyase (HL) deficiency in Brazil, South America

3-Hydroxy-3-methylglutaryl-CoA lyase (HL) deficiency (3-hydroxy-3-methylglutaric aciduria, 3-HMG) is a rare autosomal recessive inborn error of metabolism involving the final step of leucine degradation. HL is the key enzyme for the production of glucose-sparing ketone bodies for brain. Positive biochemical findings are metabolic acidosis, hyperammonaemia, and hypoketotic hypoglycaemia in the neonatal period or infancy. In the present study we report 15 Brazilian patients with HL deficiency and present their clinical and biochemical findings. Urine from all patients contained large amounts of 3-hydroxy-3-methylglutaric, 3-methylglutaconic, 3-hydroxyisovaleric and 3-methylglutaric acids, and 3-methylcrotonylglycine was also observed in 13 patients. The main features at clinical presentation were hypoglycaemia (12 patients), seizures (10 patients), metabolic acidosis (9 patients), vomiting (6 patients), and hepatomegaly (5 patients). All but two patients were of Portuguese ancestry. HL deficiency comprised 7.3% of total organic acidurias detected in our laboratory during a 13-year time span, indicating a high incidence of this disorder in Brazil. Limited molecular characterization (4/15 patients only) revealed two mutations common for individuals of Portuguese/Spanish (Iberian Peninsula) ancestry (E37X and V168fs(-2)). Our findings increase the number of HL-deficient patients and reinforce the characteristic phenotypic picture of the disease. Effective dietary interventions based on mild protein restriction and avoidance of fasting and possibly alternative C5 ketone body generating therapy for this disorder may provide further impetus and rationale for expanded newborn screening of HL deficiency.

Developmental and metabolic disorders of the pancreas

The pancreas is an important exocrine and endocrine organ that develops from the dorsal and ventral anlagen during embryogenesis and arises from the endodermal lining of the duodenum within the first month of human embryonic life. A number of developmental disorders can either lead to anatomic abnormalities of the pancreas and its ducts, or can be part of complex disorders that affect multiorgan systems. Other genetic changes can lead to metabolic abnormalities that affect the pancreas exclusively or increase the lifetime risk for developing pancreatitis or pancreatic diabetes. This article reviews some of the developmental and metabolic disorders that can affect the endocrine and exocrine pancreas.

Acute and chronic pancreatitis in patients with inborn errors of metabolism

Acute and chronic recurrent pancreatitis have been reported in patients with a variety of inborn errors of metabolism. Among these are hyperlipidaemias, various disorders of branched-chain amino acid degradation, homocystinuria, haemolytic disorders, acute intermittent porphyria and several amino acid transporter defects. Some of these disease entities are exceedingly rare. In most of these disorders, pancreatitis is not very common and, with the exception of lipoprotein lipase and apolipoprotein C-II deficiency, is neither the leading nor the clinically most distressing manifestation of the underlying metabolic defect. The majority of these syndromes are, however, inherited, and often entire kindreds are carriers of well-defined germline mutations that can, to varying degrees, be associated with pancreatitis. We have reviewed the clinical, biochemical and genetic characteristics of those inborn errors of metabolism because interesting information can be gained from the in regard to the pathophysiology of pancreatitis and because they need to be distinguished from other hereditary causes of the disease.

[3-Hydroxy-3-methyl-glutaryl-CoA-lyase deficiency as coma etiology in the neonatal period: case report]

We report a patient that presented two episodes of coma in the neonatal period, with severe metabolic acidosis and hypoglycemia, without ketosis. The urinary organic acid analysis showed increased amounts of 3-hydroxy-3-methyl-glutaric, 3-methylglutaconic, 3-methylglutaric and 3-hydroxyisovaleric acid. The deficiency of 3-hydroxy-3-methylglutaryl-CoA lyase was diagnosed by the clinical and metabolic features. This disease shows autosomal recessive inheritance and the treatment is done by a diet with restriction of protein (mainly leucine) and lipids, high in carbohydrate content, and the avoidance of fasting and carnitine supplementation.

Acute pancreatitis in an infant with lactic acidosis and a mutation at nucleotide 3243 in the mitochondrial DNA tRNALeu(UUR) gene

The A to G point mutation at position 3243 of the mitochondrial DNA tRNALeu(UUR) gene is commonly found in patients with the syndrome of mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS). A male patient was referred at 7 months with failure to thrive, developmental delay, microcephaly and hypotonia since age 2 months. He had developed lactic acidosis and increasingly frequent seizures since age 5 months. The patient was admitted at 15 months with pleural and pericardial effusions, which resolved. Three weeks later he developed evidence of pancreatitis with hyperglycemia, sudden profound increase in lactic acidosis and increased serum lipase. He died unexpectedly the next day of cardiorespiratory collapse following an acute gastro-intestinal hemorrhage. Analysis of mitochondrial DNA (mtDNA) in muscle showed heteroplasmy for the mutation MTTL1*MELAS3243G (> 95%). Infants with this mutation commonly present with failure to thrive, significant developmental delay, and hypotonia, while stroke-like episodes occur later in survivors. They usually have lactic acidosis and a high percentage of mutant mtDNA in muscle.

CONCLUSION

Respiratory chain disorders including the mtDNA MTTL1*MELAS3243G mutation should be suspected in infants with this systemic and neurologic presentation. Pancreatic dysfunction, both acute and chronic, needs to be added to the list of symptoms of disorders of the respiratory chain.

Acute basal ganglia infarction in propionic acidemia

An 8-year-old girl with propionic acidemia had acute and rapidly fatal symmetric necrosis of the caudate, globus pallidus, and putamen. Clinical presentation was with acute aphasia, generalized hypotonia, and muscle weakness. There was no evidence of metabolic decompensation, and analysis of the organic acids of the urine indicated good metabolic control. Organic acids in the cerebrospinal fluid were unremarkable. These observations indicate that the pathophysiology of "metabolic stroke" is more complicated than previously thought.

Carnitine palmitoyltransferase II deficiency: a new cause of recurrent pancreatitis

An 18-year-old female patient had a history of recurrent pancreatitis after prolonged periods of exercise coupled with a high-fat diet at the ages of 12 and 15 years. After the onset of recurrent myoglobinuria when she was 16 years old, deficiency of carnitine palmitoyltransferase type II (32% residual activity) was diagnosed on the basis of cultured skin fibroblasts. We conclude that deficiency of carnitine palmitoyltransferase type II may be a cause of pancreatitis and should be considered in the differential diagnosis, even in the absence of overt myoglobinuria.

Pancreatitis in patients with organic acidemias

STUDY OBJECTIVE

The discovery of pancreatitis in two children with methylmalonic acidemia led us to review the experience with pancreatitis in a large number of patients with organic acidemias to determine whether pancreatitis is an important complication of these disorders.

DESIGN

Case series.

SETTING

Pediatric metabolism services at five tertiary care centers.

PATIENTS

Records of all patients with organic acidemias followed at the five institutions during the past 10 years were reviewed. Pancreatitis was recognized by symptoms and laboratory findings and confirmed by imaging studies, surgery, or autopsy. At three institutions all cases of pancreatitis in children younger than 10 years were reviewed.

MEASUREMENTS AND RESULTS

Nine children with pancreatitis (seven with acute and two with chronic cases) were identified among 108 children with branched-chain organic acidemias. They ranged in age from 13 months to 9 years. Five had methylmalonic acidemia, three had isovaleric acidemia, and one had maple syrup urine disease. There were three deaths; acute hemorrhagic pancreatitis occurred in two children, and chronic pancreatitis was found at autopsy in a third. All three patients with isovaleric acidemia and pancreatitis were identified after the occurrence of pancreatitis. The survey of pancreatitis at three institutions found 57 other patients (none with an inborn error) in addition to three patients with inborn errors included in this study.

CONCLUSIONS

Acute or chronic pancreatitis may complicate branched-chain organic acidemias and must be considered in the assessment of patients with these disorders who have acute clinical deterioration and vomiting, abdominal pain, encephalopathy or shock, or milder symptoms. Conversely, an inborn error of organic acid metabolism should be considered in children with pancreatitis of unknown origin.

The contribution of protein catabolism to metabolic decompensation in 3-hydroxy-3-methylglutaric aciduria

Leucine and protein metabolism were studied using stable isotope techniques in 6-year-old twins with 3-hydroxy-3-methylglutaric aciduria during acute metabolic decompensation. The decompensation was preceded by prolonged fasting in twin 1 and by an upper respiratory infection in twin 2. Twin 2 was also studied when well (control study). During infection, leucine oxidation (36 mumol/kg per hour), protein catabolism (6.0 g/kg per day) and urinary excretion of major leucine metabolites (104 mumol/kg per hour) were all increased compared with the control study (16 mumol/kg per hour, 4.7 g/kg per day and 28 mumol/kg per hour respectively). During fasting, leucine oxidation (18 mumol/kg per hour) was unchanged and protein catabolism (4.1 g/kg per day) was decreased despite substantially increased urinary metabolite excretion (87 mumol/kg per hour) compared with the control study. These results indicate that protein mobilisation and leucine oxidation played important roles in metabolic decompensation during infection but not during fasting. It is likely that the increased metabolite excretion during fasting arose primarily from fatty acid catabolism, indicating the importance of this substrate in metabolic decompensation in 3-hydroxy-3-methylglutaric aciduria.

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: biochemical studies and family investigation of four generations

3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) lyase activity was determined by the recently described spectrophotometric method of Wanders et al. (1988a) in polymorphonuclear leukocytes and lymphocytes obtained from 33 members of a highly consanguineous Arab-Bedouin family belonging to four generations. Seven subjects were obligatory heterozygotes (parents and grandparents of three propositi); in seven additional subjects enzyme activity in both cell types was in the heterozygote range. No asymptomatic homozygotes were found. The results support the proposed autosomal recessive mode of inheritance of this disorder.

Management of chronic relapsing pancreatitis in adolescents

Chronic relapsing pancreatitis in adolescence is a most uncommon clinical problem and has received minimal separate recognition in the literature. Adolescence is an age when the causes of the disease, which may operate from birth, overlap with the major etiological factors in the generality of pancreatitis in adult life. A personal series of 32 patients with pancreatitis, aged 11-20 years, is reported. Twenty-four followed a chronic relapsing course. There was, therefore, a marked reversal of the normal preponderance of acute over chronic relapsing cases. Those with underlying biliary disease, and the group in whom no etiological factors could be identified, ran an unexpectedly severe and troublesome course. This, coupled with the reversal of the acute versus chronic disease ratio, raises the question as to whether adolescent pancreatitis is a distinct subgroup in the overall spectrum of this disease.

Inborn errors of amino acid and fatty acid metabolism with hypoglycemia as a major clinical manifestation

During the last decade it has become increasingly clear that severe hypoglycemia may be caused by specific enzymatic defects of amino acid and fatty acid metabolism. Several reports have presented hypoglycemic syndromes with reduced fatty acid transport or oxidation, decreased ketogenesis, or abnormalities of the Krebs cycle and electron transport chain. It is of particular interest that several enzymatic defects here discussed may present as Reye's syndrome. An intriguing fact is a highly variable clinical presentation, even in the presence of well-defined enzyme deficiencies. Some patients are desperately ill in the newborn period, whereas in other cases there are symptoms only during catabolic phases later in childhood. The presence of hypoglycemia may be related to low levels of acetyl CoA, with consequently reduced gluconeogenesis; alternatively the glucose-sparing effect of ketones is lost in states of reduced ketone body production. Treatment with pharmacological doses of vitamins may be attempted, depending upon the established or suspected diagnoses. With manifest hypoglycemia i.v. glucose infusion is the treatment of choice. By such means convulsions, and brain damage may be prevented.

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: review of 18 reported patients

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMG-CoA lyase) is an inborn error of leucine catabolism which often leads to life-threatening illness in the neonatal period. The cardinal clinical features include severe infantile hypoglycemia, metabolic acidosis, hepatomegaly, lethargy or coma and apnea. Hyperammonemia is variable. There is a characteristic absence of ketosis. Considerable heterogeneity has been observed in clinical and biochemical presentation. Acute episodes of illness have been mistaken for Reye syndrome. The pattern of organic acids in the urine includes large amounts of 3-hydroxy-3-methylglutaric, 3-methyl-glutaconic, 3-methylglutaric and 3-hydroxyisovaleric acids. Smaller, but appreciable levels of glutaric, adipic and other dicarboxylic acids may also be excreted in the urine. Lactic acid may be present in sizable amounts at times of acute illness. The primary defect is a deficiency of 3-hydroxy-3-methylglutaryl-coenzyme A lyase, a key enzyme in the cycle of ketogenesis.

3-Hydroxy-3-methylglutaryl-CoA lyase in human skin fibroblasts: study of its properties and deficient activity in 3-hydroxy-3-methylglutaric aciduria patients using a simple spectrophotometric method

In this paper we studied the properties of 3-hydroxy-3-methylglutaryl-CoA lyase (HMG-CoA lyase) in human skin fibroblasts. The enzyme was found to exhibit an absolute requirement for divalent cations such as magnesium. Furthermore, dithiothreitol was necessary for full activity. The enzyme was found to be maximally active at pH 9.25. When measured at this pH in the presence of magnesium and dithiothreitol enzyme activity was high enough to be determined by simple spectrophotometry by measuring the amounts of acetoacetate produced. The results obtained suggest that the large variation in the values reported in literature for the activity of HMG-CoA lyase in human skin fibroblasts is due to the fact that the enzyme shows little activity at pH values below 8.

3-Hydroxy-3-methylglutaric aciduria: response to carnitine therapy and fat and leucine restriction

A female infant, born to first cousin parents, lapsed into coma with severe metabolic acidosis on day three of life. The gas chromatographic/mass spectrometric urinary organic acid profile showed marked elevation of the leucine metabolites 3-hydroxy-3-methylglutaric, 3-methylglutaconic, 3-methylglutaric and 3-hydroxy-isovaleric acids. Less than 5% of the normal activity of the enzyme 3-hydroxy-3-methylglutaryl CoA lyase was detected in cultured skin fibroblasts. The patient's total and free carnitine was initially low but rose to normal levels after placing her on DL-carnitine (100 mg kg-1 d-1). On a diet providing 87 mg kg-1 d-1 of leucine and only 25% of total calories as fat and 2 g kg-1 d-1 protein, the concentration of the urinary organic acids fell markedly. She is now 15 months old with normal growth and development. This regimen appears effective in the early treatment of 3-hydroxy-3-methylglutaric aciduria.

Atypical presentation and neuropathological studies in 3-hydroxy-3-methylglutaryl-CoA lyase deficiency

A 6 1/2-month-old male offspring of consanguineous Egyptian parents was first seen because of fever, somnolence, vomiting, right focal motor seizures, right hemiparesis, elevated transaminase levels, hyperammonemia, and acidosis. A computed tomographic scan of the head suggested swelling of the left cerebral hemisphere, and an electroencephalogram indicated left frontotemporal abnormalities, but brain biopsy demonstrated diffuse white matter spongiosis and gliosis. Subsequently, urine organic acid analysis and enzyme assays were diagnostic of 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency.

3-Hydroxy-3-methylglutaryl-coenzyme a lyase deficiency: a review

Children with 3-hydroxy-3-methylglutaryl-CoA lyase deficiency (HMG-CoA-LD; McKusick 24645), have inherited two areas of metabolic weakness. Firstly, they are unable to metabolize fully the carbon skeleton of leucine, and secondly, they cannot make ketone bodies in response to prolonged fasting. In the first year of life infants with HMG-CoA-LD run a high risk of developing severe hypoglycaemia which can lead to death if prompt intervention does not occur. The metabolic crisis develops when the infant is first introduced to dietary protein soon after birth, or later, when a reduced intake of glucose, often during a viral infection, results in a drain on the infant's circulating glucose levels. However, where diets are adequately adjusted to limit protein and fat intake, the metabolic handicaps of individuals with HMG-CoA-LD are not exposed and they are virtually symptomless. As children with HMG-CoA-LD grow older the incidence of hypoglycaemic attacks diminishes and they usually develop normally. This article reviews literature on cases of HMG-CoA-LD and interprets data on altered metabolism in these children.

Metabolism of leucine in fibroblasts from patients with deficiencies in each of the major catabolic enzymes: branched-chain ketoacid dehydrogenase, isovaleryl-CoA dehydrogenase, 3-methylcrotonyl-CoA carboxylase, 3-methylglutaconyl-CoA hydratase, and 3-hydroxy-3-methylglutaryl-CoA lyase

The metabolism of leucine was studied in cultured human fibroblasts derived from patients with defects in each of the major steps in the catabolism of the amino acid. Intact fibroblasts were incubated with [U-14C]leucine and the organic acid products were isolated by liquid partition chromatography. In control fibroblasts the major product of leucine was 3-hydroxyisovaleric acid. This was also the case for fibroblasts with deficiency of 3-hydroxy-3-methylglutaryl-CoA lyase, 3-methylcrotonyl-CoA carboxylase and 3-methylglutaconyl-CoA hydratase. There was little or no accumulation of the compound with fibroblasts from patients with maple syrup urine disease and isovaleric acidemia.