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BACKGROUND: Cystinosis is an autosomal recessive disorder marked by intralysosomal cystine accumulation. Patients present with generalized proximal tubular dysfunction called renal Fanconi syndrome. Urinary carnitine loss results in plasma and muscle carnitine deficiency, but no clinical signs of carnitine deficiency have been described. Also, the optimal dose of carnitine supplementation is undefined. This study aimed to determine whether currently recommended carnitine doses result in adequate correction of plasma carnitine. METHODS: Five cystinosis patients with renal Fanconi syndrome, aged 2-18 years, were included. L-carnitine was prescribed 50 mg/kg/day since diagnosis: median 36 (range 18-207) months. Total and free plasma and urine carnitine and carnitine profiles were measured at study onset, after stopping L-carnitine for 3 months and 3 months after reintroducing L-carnitine 50 mg/kg/day. RESULTS: At study onset, plasma free carnitine was normal in all patients, total carnitine (1/5), acetylcarnitine (3/5), and several short- and medium-chain acylcarnitines ≤10 carbons (5/5) were increased indicating carnitine over-supplementation. Three months after cessation, carnitine profiles normalized and 3/5 patients showed plasma carnitine deficiency. Three months after reintroduction, plasma free carnitine normalized in all patients, however, carnitine profiles were disturbed in 4/5 patients. Urine free carnitine, acetylcarnitine, and acylcarnitines ≤10 carbons were increased in all patients independent of carnitine supplementation. CONCLUSION: Administration of recommended doses L-carnitine (50 mg/kg/day) resulted in over-supplementation. Although the drug is considered to be rather safe, long-term effects of over-supplementation remain unknown warranting cautious use of high doses. Plasma carnitine profile might be used as a monitor, to prevent overdosing.

Abnormal carnitine distribution in muscle was found in 22 of 77 patients (29%), with mitochondrial myopathy. Furthermore, total (TC) and free (FC) carnitine levels in muscle were lower in patients than in controls (P < 0.01). Muscle long-chain acylcarnitines (LCAC) were significantly increased in these patients (P < 0.01). Muscle carnitine deficiency was found in 31.5% of patients with lipid storage myopathy (LSM) and in 25.6% of patients with ragged-red fibers (RRF). Therefore, carnitine deficiency can be found in patients with mitochondrial myopathy even in the absence of LSM. Muscle levels of TC and FC were lower in patients with respiratory chain defects than in those with normal respiratory chain (P < 0.01). In contrast, LCAC levels were significantly increased (P < 0.05). Carnitine levels did not differ significantly, among patients with different respiratory-chain defects. Consequently, these patients, owing to their biochemical block, reduce progressively the muscle carnitine pool and subsequent LCAC rise, due to long-chain fatty acid (LCFA) accumulation.

Muscle carnitine deficiency usually results in a lipid storage myopathy, but more rarely, neuropathy occurs in this condition. We report herein a 29-year-old man with muscle carnitine deficiency who developed not only a lipid storage myopathy, but also a severe sensory neuropathy. Oral therapy with levo-carnitine (3 g per day) for 3 months produced a remarkable improvement of the myopathy and sensory neuropathy. Six months later, he remained in good condition under strict dietary control. This report emphasizes that severe neuropathy may occur in some patients with muscle carnitine deficiency, and highlights the need for the neurologist’s familiarity with those afflicted to achieve optimal clinical management.

BACKGROUND This study was designed to evaluate the effect of severe peripheral arterial insufficiency on carnitine concentrations and carnitine acetyltransferase and palmitoyltransferase activities in the ischemic skeletal muscles of patients with severe peripheral vascular disease. METHODS AND RESULTS Nine biopsy specimens of ischemic muscles were obtained from five patients undergoing reconstructive vascular surgery. Biopsies from 35 normal subjects served as controls. Ischemic muscles showed a significant reduction in total carnitine from the control value of 20.9 +/- 5.2 to 11.6 +/- 6.2 nmol/mg noncollagen protein (p less than 0.01). A significantly lower free carnitine and acylcarnitine content contributed to this reduction. Similarly, carnitine acetyltransferase activity was reduced in the ischemic muscles from the control value of 102.1 +/- 41.2 to 52.9 +/- 22.1 nmol/min/mg noncollagen protein (p less than 0.01). On the contrary, carnitine palmitoyltransferase activity did not show any change (0.29 +/- 0.05 nmol/min/mg noncollagen protein in the ischemic muscles and 0.28 +/- 0.07 nmol/min/mg noncollagen protein in controls). Carnitine, acylcarnitines, and enzyme activities were also measured in the ischemic muscles in four additional patients 2 days after intravenous administration of L-propionylcarnitine (1.5 g as a single bolus followed by an infusion of 1 mg/kg/min for 30 minutes). Treatment restored normal levels of carnitine and its esters in the ischemic muscles but did not affect enzyme activities. CONCLUSIONS Demonstration of carnitine deficiency in severe peripheral vascular disease substantiates previous findings showing the efficacy of carnitine supplementation to ischemic muscles. Furthermore, the feasibility of restoring carnitine homeostasis with L-propionylcarnitine provides the basis for clinical trials aimed at assessing the efficacy of this carnitine ester in the treatment of peripheral vascular disease.

The human primary carnitine deficiency syndromes are potentially fatal disorders affecting children and adults. The molecular etiologies of these syndromes have not been fully determined. Muscle carnitine deficiency syndrome is characterized by mild to severe muscle weakness, lipid accumulation in muscle, and reduced muscle carnitine concentration. In the present investigation, the hexose transport properties of muscle cells isolated from a patient with suspected muscle carnitine deficiency (MCD) were examined. We have previously shown that myoblasts from normal human subjects possessed at least two hexose transport systems, the low (LAHT) and the high (HAHT) affinity hexose transport systems. Their preferred substrates were 3-O-methyl-D-glucose and 2-deoxyglucose (dGlc), respectively; HAHT, but not LAHT, was sensitive to inhibition by carbonyl cyanide m-chlorophenylhydrazone (CCCP). Here we show that the kinetic properties of HAHT in the MCD myoblasts differ significantly from those of normal myoblasts and that the rates of dGlc transport by MCD myoblasts are restored to normal by growth in 40 μM L-carnitine. We also demonstrate that the kinetic properties of LAHT are quite similar in both normal and MCD myoblasts. It can be inferred from these findings that HAHT and LAHT may be coded or regulated by different genes. Based on the finding that the dGlc transport system in L-carnitine grown cells is no longer sensitive to inhibition by CCCP, it is thought that L-carnitine may play a regulatory role in HAHT, viz., by maintaining the HAHT transporter in a functional state, even in energy-uncoupled cells. While MCD myoblasts exhibit normal rates of L-carnitine influx, their L-carnitine efflux rates are significantly faster than those of normal myoblasts, thus resulting in significantly reduced intracellular level of L-carnitine in the MCD myoblasts. This reduced intracellular L-carnitine level would then explain the relatively reduced HAHT activity and its subsequent restoration to normal activity following growth in L-carnitine.Key words: hexose transport, human myoblasts, muscle carnitine deficiency, myopathy, human genetic variants, myoblasts, transport regulation, β-oxidation, L-carnitine.

Two types of lipid storage myopathy have been associated with decreased content of carnitine in muscle. In “muscle carnitine deficiency”, carnitine concentration is normal in serum, but reduced in muscle. In “systemic carnitine deficiency”, apparently due to impaired synthesis of carnitine in the liver, carnitine content is low in both serum and muscle. We studied a woman with a corticosteroid-responsive, probably autosomal recessive, lipid storage myopathy. Carnitine therapy was ineffective and carnitine failed to correct the impaired fatty acid oxidation in muscle homogenates, in contrast to a previous case. Carnitine transport into skeletal muscle was normal. These observations suggest that all cases of “muscle carnitine deficiency” are not the same.

The present study investigates 14 patients on intermittent haemodialysis. Pre-dialysis blood and muscle samples taken for determining plasma free- and acetylcarnitine levels. The tissue fragments were used for light and electron microscopy studies. Our results support the findings of other investigators that patients on haemodialysis generally display decreased free- and acetylcarnitine levels both in plasma and skeletal muscle when compared with control values. Muscle carnitine deficiency was apparently more severe in the longer-term haemodialysis patients. Moreover, a significant correlation (p less than 0.05) between plasma and muscle free-carnitine values was found. Morphologically no pathological alterations were observed in the muscle fibres in 13 of the patients. Light and electron microscopic studies of the muscle fibre of the 14th patient showed a typical nemaline myopathy with rod bodies in the cytoplasm. The muscle free-carnitine concentration in this patient was among the lowest of the group.

Three siblings presented with fatal cardiomyopathy confirmed by electron microscopy, and normal serum but low muscle carnitine concentrations. A fourth had similar signs but remained asymptomatic. He was treated with carnitine orally which increased the concentration in muscle, though it remained below normal. Electron microscopic features were unchanged.

A 23-month-old boy with progressive muscle weakness and severe cardiomyopathy was found to have oil red O positive vacuoles predominantly in type 1 muscle fibers. Serum carnitine was normal, but muscle carnitine content was decreased. Both parents were clinically normal, but the muscle carnitine level was low in the father. Despite oral treatment with carnitine, the condition progressed and was fatal. At autopsy, cardiac muscle showed borderline low carnitine content and numerous mitochondria, but no lipid accumulation.

The levels of plasma free carnitine and ketone bodies have been found to fluctuate inversely in fasting individuals without muscle disease. Circulating short-chain acyl-carnitines paralleled beta-hydroxybutyrate levels. A patient with lipid storage myopathy and muscle carnitine deficiency, and his two daughters, developed exaggerated ketogenesis on fasting. The content of total carnitines in the patient's liver was normal, but free carnitine was reduced to 50 percent, and total esterified carnitines were four times greater than the mean value for the controls. The decreased muscle carnitine content in this case may have resulted from chronic hepatic ketogenesis, draining muscle carnitine. Alternatively, decreased muscle carnitine content may have initiated hepatic ketogenesis.