162nd ENMC International Workshop: Disorders of muscle lipid metabolism in adults 28–30 November 2008, Bussum, The Netherlands

Long-term prognosis of fatty-acid oxidation disorders in adults: Optimism despite the limited effective therapies available

INTRODUCTION

Fatty-acid oxidation disorders (FAODs) are recessive genetic diseases.

MATERIALS AND METHODS

We report here clinical and paraclinical data from a retrospective study of 44 adults with muscular FAODs from six French reference centers for neuromuscular or metabolic diseases.

RESULTS

The study cohort consisted of 44 adult patients: 14 with carnitine palmitoyl transferase 2 deficiency (32%), nine with multiple acyl-CoA deficiency (20%), 13 with very long-chain acyl-CoA dehydrogenase deficiency (30%), three with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (7%), and five with short-chain acyl-CoA dehydrogenase deficiency (11%). Disease onset occurred during childhood in the majority of patients (59%), with a mean age at onset of 15 years (range = 0.5-35) and a mean of 12.6 years (range = 0-58) from disease onset to diagnosis. The principal symptoms were acute muscle manifestations (rhabdomyolysis, exercise intolerance, myalgia), sometimes associated with permanent muscle weakness. Episodes of rhabdomyolysis were frequent (84%), with a mean creatinine kinase level of 68,958 U/L (range = 660-300,000). General metabolic complications were observed in 58% of patients, respiratory manifestations in 18% of cases, and cardiological manifestations in 9% of cases. Fasting acylcarnitine profile was used to orient genetic explorations in 65% of cases. After a mean follow-up of 10 years, 33% of patients were asymptomatic and 56% continued to display symptoms after exercise. The frequency of rhabdomyolysis decreased after diagnosis in 64% of cases.

CONCLUSION

A standardized register would complete this cohort description of muscular forms of FAODs with exhaustive data, making it possible to assess the efficacy of therapeutic protocols in real-life conditions and during the long-term follow-up of patients.

Carnitine palmitoyltransferase type 2 deficiency: novel mutation in a Native South American family with whole-body muscle magnetic resonance imaging findings: two case reports

Background

The myopathic form of carnitine palmitoyltransferase type II deficiency is an inherited autosomal recessive metabolic myopathy usually starting in childhood. Most reports have been on European and Japanese populations, and no Native South American patients have been reported to date. The p.Ser113Leu mutation is the most frequent in the European population. Only lower-leg magnetic resonance imaging findings have been reported, with gluteus maximus involvement in one case and normal imaging in other patients.

Case presentation

Two Native South American siblings, a boy and a girl, presented to our neuromuscular clinic with recurrent rhabdomyolysis associated with transient muscle weakness after prolonged exercise. During episodes, their creatine kinase concentrations were markedly increased, up to 148,000 (1.48 × 10⁵) IU/L in the boy and 18,000 (1.8 × 10⁴) IU/L in the girl. The results of electroneuromyography and histopathology suggested a nonspecific myopathy. CPT2 gene sequencing showed two heterozygous mutations: the p.Ser113Leu variant and a novel one (predicted to be deleterious by in silico analysis), the p.Ser373Pro variant. The patients’ parents were asymptomatic carriers. Whole-body magnetic resonance imaging showed mild selective involvement in the thoracic extensors and pelvic girdle in both siblings, and in the thighs and lower legs in one of them. Dietary and bezafibrate treatment was started, and symptomatic relief was observed.

Conclusions

To the best of our knowledge, this is the first reported Native South American family with a CPT2 deficiency carrying a novel mutation and particular features visualized by whole-body magnetic resonance imaging.

Update on clinical aspects and treatment of selected vitamin-responsive disorders II (riboflavin and CoQ 10)

Riboflavin and ubiquinone (Coenzyme Q(10), CoQ(10)) deficiencies are heterogeneous groups of autosomal recessive conditions affecting both children and adults. Riboflavin (vitamin B(2))-derived cofactors are essential for the function of numerous dehydrogenases. Genetic defects of the riboflavin transport have been detected in Brown-Vialetto-Van Laere and Fazio-Londe syndromes (C20orf54), and haploinsufficiency of GPR172B has been proposed in one patient to cause persistent riboflavin deficiency. Mutations in the electron tranferring fravoprotein genes (ETFA/ETFB) and its dehydrogenase (ETFDH) are causative for multiple acyl-CoA dehydrogenase deficiency. Mutations in ACAD9, encoding the acyl-CoA dehydrogenase 9 protein were recently reported in mitochondrial disease with respiratory chain complex I deficiency. All these conditions may respond to riboflavin therapy. CoQ(10) is a lipid-soluble component of the cell membranes, where it functions as a mobile electron and proton carrier, but also participates in other cellular processes as a potent antioxidant, and by influencing pyrimidine metabolism. The increasing number of molecular defects in enzymes of the CoQ(10) biosynthetic pathways (PDSS1, PDSS2, COQ2, COQ6, COQ9, CABC1/ADCK3) underlies the importance of these conditions. The clinical heterogeneity may reflect blocks at different levels in the complex biosynthetic pathway. Despite the identification of several primary CoQ(10) deficiency genes, the number of reported patients is still low, and no true genotype-phenotype correlations are known which makes the genetic diagnosis still difficult. Additionally to primary CoQ(10) deficiencies, where the mutation impairs a protein directly involved in CoQ(10) biosynthesis, we can differentiate secondary deficiencies. CoQ(10) supplementation may be beneficial in both primary and secondary deficiencies and therefore the early recognition of these diseases is of utmost importance.

Disorders of muscle lipid metabolism: diagnostic and therapeutic challenges

Disorders of muscle lipid metabolism may involve intramyocellular triglyceride degradation, carnitine uptake, long-chain fatty acids mitochondrial transport, or fatty acid β-oxidation. Three main diseases leading to permanent muscle weakness are associated with severe increased muscle lipid content (lipid storage myopathies): primary carnitine deficiency, neutral lipid storage disease and multiple acyl-CoA dehydrogenase deficiency. A moderate lipidosis may be observed in fatty acid oxidation disorders revealed by rhabdomyolysis episodes such as carnitine palmitoyl transferase II, very-long-chain acyl-CoA dehydrogenase, mitochondrial trifunctional protein deficiencies, and in recently described phosphatidic acid phosphatase deficiency. Respiratory chain disorders and congenital myasthenic syndromes may also be misdiagnosed as fatty acid oxidation disorders due to the presence of secondary muscle lipidosis. The main biochemical tests giving clues for the diagnosis of these various disorders are measurements of blood carnitine and acylcarnitines, urinary organic acid profile, and search for intracytoplasmic lipid on peripheral blood smear (Jordan's anomaly). Genetic analysis orientated by the results of biochemical investigation allows establishing a firm diagnosis. Primary carnitine deficiency and multiple acyl-CoA dehydrogenase deficiency may be treated after supplementation with carnitine, riboflavine and coenzyme Q10. New therapeutic approaches for fatty acid oxidation disorders are currently developed, based on pharmacological treatment with bezafibrate, and specific diets enriched in medium-chain triglycerides or triheptanoin.