Infantile phosphofructokinase deficiency with arthrogryposis: clinical benefit of a ketogenic diet

Recent aspects of ketogenic diet in neurological disorders

The ketogenic diet (KD) is a high-fat, low-carbohydrate diet, in which fat is used as the primary energy source through the production of ketone bodies (KBs) in place of glucose. The KD was formally introduced in 1921 to mimic the biochemical changes associated with fasting and gained recognition as a potent treatment for pediatric epilepsy in the mid-1990s. The clinical and basic scientific knowledge that supports the anti-seizure efficacy, safety, and feasibility of using the KD in patients with epilepsy is huge. Additionally, the International Ketogenic Diet Study Group’s consensus guidelines provide practical information in 2009 and 2018. The KD is a broad-spectrum therapy for drug resistant epilepsy and is gaining attention as a potential therapy for other neurological disorders. This article will review recent aspects on the use of the KD, including its mechanisms of action, KD alternatives, expanding its use across different age groups and regions, its use as a treatment for other neurologic disorders, and future research subjects.

Beneficial Effects of Ketogenic Diet on Phosphofructokinase Deficiency (Glycogen Storage Disease Type VII)

Background: A deficiency of muscle phosphofructokinase (PFKM) causes a rare metabolic muscle disease, the Tarui disease (Glycogen storage disease type VII, GSD VII) characterized by exercise intolerance with myalgia due to an inability to use glucose as an energy resource. No medical treatment for GSD VII currently exists. The aim of this study was to determine whether a dietary intervention with excessive fat intake would benefit GSD VII.

Patient and Methods: A ketogenic diet (KD) intervention implemented as a modified Atkins diet was established for one patient with PFKM deficiency, with a low late lactate response and very high ammonia levels associated with exercise. We recorded the KD intervention for a total of 5 years with clinical and physiotherapeutic evaluations and regular laboratory parameters. Cardiopulmonary exercise testing, including breath gas analysis and venous lactate and ammonia measurements, was performed before KD and at 3, 8 months and 5 years after initiation of KD.

Results: During the 5 years on KD, the patient's muscle symptoms had alleviated and exercise tolerance had improved. In exercise testing, venous ammonia had normalized, the lactate profile remained similar, but oxygen uptake and mechanical efficiency had increased and parameters showing ventilation had improved.

Conclusions: This study is the first to show a long-term effect of KD in GSD VII with an alleviation of muscle symptoms, beneficial effects on breathing, and improvement in exercise performance and oxygen uptake. Based on these findings, KD can be recommended under medical and nutritional supervision for selected patients with GSD VII, although further research of this rare disease is warranted.

Optimal clinical management of children receiving dietary therapies for epilepsy: Updated recommendations of the International Ketogenic Diet Study Group

Ketogenic dietary therapies (KDTs) are established, effective nonpharmacologic treatments for intractable childhood epilepsy. For many years KDTs were implemented differently throughout the world due to lack of consistent protocols. In 2009, an expert consensus guideline for the management of children on KDT was published, focusing on topics of patient selection, pre‐KDT counseling and evaluation, diet choice and attributes, implementation, supplementation, follow‐up, side events, and KDT discontinuation. It has been helpful in outlining a state‐of‐the‐art protocol, standardizing KDT for multicenter clinical trials, and identifying areas of controversy and uncertainty for future research. Now one decade later, the organizers and authors of this guideline present a revised version with additional authors, in order to include recent research, especially regarding other dietary treatments, clarifying indications for use, side effects during initiation and ongoing use, value of supplements, and methods of KDT discontinuation. In addition, authors completed a survey of their institution's practices, which was compared to responses from the original consensus survey, to show trends in management over the last 10 years.

Ketogenic diets in patients with inherited metabolic disorders

Ketogenic diets (KDs) are diets that bring on a metabolic condition comparable to fasting, usually without catabolism. Since the mid-1990s such diets have been widely used in patients with seizures/epilepsies, mostly children. This review focuses on the use of KDs in patients with various inherited metabolic disorders (IMD). In glucose transporter type 1 deficiency syndrome (GLUT1-DS) and pyruvate dehydrogenase complex (PDHc) deficiency, KDs are deemed the therapy of choice and directly target the underlying metabolic disorder. Moreover, in other IMD, mainly of intermediary metabolism such as glycogen storage diseases and disorders of mitochondrial energy supply, KDs may ameliorate clinical symptoms and laboratory parameters. KDs have also been used successfully to treat symptoms such as seizures/epilepsy in IMD, e.g. in urea cycle disorders and non-ketotic hyperglycinemia. As a note of caution, catabolism may cause the condition of patients with IMD to deteriorate and should thus be avoided during KDs. For this reason, careful monitoring (clinical, laboratory and apparatus-supported) is warranted. In some IMDs specific macronutrient supply is critical. Therefore, in cases of PDHc deficiency the carbohydrate intake tolerated without lactate increase and in urea cycle disorders the protein tolerance should be determined. Considering this, it is particularly important in patients with IMD that the use of KDs be individualized and well documented.

An update on diets in clinical practice

Ketogenic diet therapies involve a collaborative healthcare team and therefore are typically offered in tertiary care centers. Centers that utilize these therapies with frequency gain valuable experience and become skilled in their practice. This chapter is a summary from the presentations of 5 practitioners including a nurse, pharmacist, and 3 dietitians who shared their expertise during the clinical session of the 2012 International Symposium.

The use of ketogenic diet in special situations: expanding use in intractable epilepsy and other neurologic disorders

The ketogenic diet has been widely used and proved to be effective for intractable epilepsy. Although the mechanisms underlying its anti-epileptic effects remain to be proven, there are increasing experimental evidences for its neuroprotective effects along with many researches about expanding use of the diet in other neurologic disorders. The first success was reported in glucose transporter type 1 deficiency syndrome, in which the diet served as an alternative metabolic source. Many neurologic disorders share some of the common pathologic mechanisms such as mitochondrial dysfunction, altered neurotransmitter function and synaptic transmission, or abnormal regulation of reactive oxygen species, and the role of the ketogenic diet has been postulated in these mechanisms. In this article, we introduce an overview about the expanding use and emerging trials of the ketogenic diet in various neurologic disorders excluding intractable epilepsy and provide explanations of the mechanisms in that usage.

Ketogenic diet in early myoclonic encephalopathy due to non ketotic hyperglycinemia

Non ketotic hyperglycinemia is a rare inborn error of glycine metabolism due to deficient activity of glycine cleavage system, a multienzymatic complex consisting of four protein subunits: the P-protein, the H-protein, the T-protein and the L-protein. The neonatal form of non ketotic hyperglycinemia presents in the first days of life with encephalopathy, seizures, multifocal myoclonus and characteristic "hiccups". Rapid progression may lead to intractable seizures, coma and respiratory failure requiring mechanical ventilation. Clinical trial with scavenges drugs decreasing glycine levels such as sodium benzoate, and with drugs reducing NMDA receptors excitatory properties, such as ketamine and dextromethorphan, have been tried but the outcome is usually poor; antiepileptic therapy, moreover, is unable to control epileptic seizures. Ketogenic diet has been successfully tried for refractory epilepsy in pediatric patients. We report three cases affected by neonatal non ketotic hyperglycinemia and early myoclonic encephalopathy treated with ketogenic diet. In our patients ketogenic diet, in association with standard pharmacological therapy, determined dramatic reduction of seizures and improved quality of life.

Dietary treatment of epilepsy: rebirth of an ancient treatment

Since its introduction in 1921, the ketogenic diet has been in continuous use for children with difficult-to-control epilepsy. After decades of relative disuse, it is now both extremely popular and well studied, with approximately two-thirds of children demonstrating significant seizure reduction after 6 months. It is being used for less intractable seizures in children as well as recently adults. Modifications that help improve tolerability include the medium chain triglyceride diet, modified Atkins diet, and low glycemic index treatment. Major side effects include acidosis, increased cholesterol, kidney stones, gastroesophageal reflux, and growth disturbance. However, these side effects are usually treatable and nowadays often even preventable. Future non-epilepsy indications such as Alzheimer disease, amyotrophic lateral sclerosis, autism, and brain tumors are under active investigation. This dietary treatment for epilepsy has undergone a rebirth. Its widespread use in Poland and Europe is a welcome additional treatment for those with drug-resistant epilepsy.

Metabolic disorders of fetal life: glycogenoses and mitochondrial defects of the mitochondrial respiratory chain

Two major groups of inborn errors of energy metabolism are reviewed -glycogenoses and defects of the mitochondrial respiratory chain - to see how often these disorders present in fetal life or neonatally. After some general considerations on energy metabolism in the pre- and postnatal development of the human infant, different glycogen storage diseases and mitochondrial encephalomyopathies are surveyed. General conclusions are that: (i) disorders of glycogen metabolism are more likely to cause 'fetal disease' than defects of the respiratory chain; (ii) mitochondrial encephalomyopathies, especially those due to defects of the nuclear genome, are frequent causes of neonatal or infantile diseases, typically Leigh syndrome, but usually do not cause fetal distress; (iii) notable exceptions include mutations in the complex III assembly gene BCS1L resulting in the GRACILE syndrome (growth retardation, aminoaciduria, cholestasis, iron overload, lactic acidosis, and early death), and defects of mitochondrial protein synthesis, which are the 'new frontier' in mitochondrial translational research.

Metabolic myopathies: clinical features and diagnostic approach

The rheumatologist is frequently called on to evaluate patients with complaints of myalgia, muscle cramps, and fatigue. The evaluation of these patients presents a diagnostic challenge given the nonspecific and intermittent nature of their complaints, often leading to inappropriate diagnostic testing. When these symptoms are associated with physical exertion, a metabolic myopathy should be suspected Although inflammatory myopathies may present with similar features, such a pattern should prompt a thorough evaluation for an underlying metabolic myopathy. This review discusses the most common causes of metabolic myopathies and reviews the current diagnostic options available to the clinician.

Long-term follow-up of the ketogenic diet for refractory epilepsy: multicenter Argentinean experience in 216 pediatric patients

PURPOSE

In this Argentinean retrospective, collaborative, multicenter study, we examine the efficacy and tolerability of the ketogenic diet (KD) for different epilepsy syndromes.

MATERIALS AND METHODS

we evaluated the clinical records of 216 patients started on the KD between March 1, 1990 and December 31, 2010.

RESULTS

One hundred forty of the initial patients (65%) remained on the diet at the end of the study period. Twenty-nine patients (20.5%) became seizure free and 50 children (36%) had a 75-99% decrease in seizures. Thus, 56.5% of the patients had a seizure control of more than 75%. The best results were found in patients with epilepsy with myoclonic-astatic seizures, Lennox-Gastaut syndrome, and West syndrome. Good results were also found in patients with Dravet syndrome, in those with symptomatic focal epilepsy secondary to malformations of cortical development, and in patients with tuberous sclerosis. Seizures were significantly reduced in four patients with fever-induced refractory epileptic encephalopathy in school-age children and in two patients with epileptic encephalopathy with continuous spikes and waves during slow sleep. The median period of follow-up after discontinuation of the diet was 6 years. Twenty patients who had become seizure free discontinued the diet, but seizures recurred in five (25%). Of 40 patients with a seizure reduction of more than 50% who discontinued the diet, 10 presented with recurrent seizures.

CONCLUSION

The ketogenic diet is a good option in the treatment of refractory epilepsy. After discontinuing the diet, seizures recurrence occurred in few patients.

The ketogenic diet: uses in epilepsy and other neurologic illnesses

The ketogenic diet is well established as therapy for intractable epilepsy. It should be considered first-line therapy in glucose transporter type 1 and pyruvate dehydrogenase deficiency. It should be considered early in the treatment of Dravet syndrome and myoclonic-astatic epilepsy (Doose syndrome). Initial studies indicate that the ketogenic diet appears effective in other metabolic conditions, including phosphofructokinase deficiency and glycogenosis type V (McArdle disease). It appears to function in these disorders by providing an alternative fuel source. A growing body of literature suggests the ketogenic diet may be beneficial in certain neurodegenerative diseases, including Alzheimer disease, Parkinson's disease, and amyotrophic lateral sclerosis. In these disorders, the ketogenic diet appears to be neuroprotective, promoting enhanced mitochondrial function and rescuing adenosine triphosphate production. Dietary therapy is a promising intervention for cancer, given that it may target the relative inefficiency of tumors in using ketone bodies as an alternative fuel source. The ketogenic diet also may have a role in improving outcomes in trauma and hypoxic injuries.

Branching enzyme deficiency/glycogenosis storage disease type IV presenting as a severe congenital hypotonia: muscle biopsy and autopsy findings, biochemical and molecular genetic studies

The fatal infantile neuromuscular presentation of branching enzyme deficiency (glycogen storage disease type IV) due to mutations in the gene encoding the glycogen branching enzyme, is a rare but probably underdiagnosed cause of congenital hypotonia. We report an infant girl with severe generalized hypotonia, born at 33 weeks gestation who required ventilatory assistance since birth. She had bilateral ptosis, mild knee and foot contractures and echocardiographic evidence of cardiomyopathy. A muscle biopsy at 1 month of age showed typical polyglucosan storage. The autopsy at 3.5 months of age showed frontal cortex polymicrogyria and polyglucosan bodies in neurons of basal ganglia, thalamus, substantia innominata, brain stem, and myenteric plexus, as well as liver involvement. Glycogen branching enzyme activity in muscle was virtually undetectable. Sequencing of the GBE1 gene revealed a homozygous 28 base pair deletion and a single base insertion at the same site in exon 5. This case confirms previous observations that GBE deficiency ought to be included in the differential diagnosis of congenital hypotonia and that the phenotype correlates with the 'molecular severity' of the mutation.

Optimal clinical management of children receiving the ketogenic diet: recommendations of the International Ketogenic Diet Study Group

The ketogenic diet (KD) is an established, effective nonpharmacologic treatment for intractable childhood epilepsy. The KD is provided differently throughout the world, with occasionally significant variations in its administration. There exists a need for more standardized protocols and management recommendations for clinical and research use. In December 2006, The Charlie Foundation commissioned a panel comprised of 26 pediatric epileptologists and dietitians from nine countries with particular expertise using the KD. This group was created in order to create a consensus statement regarding the clinical management of the KD. Subsequently endorsed by the Practice Committee of the Child Neurology Society, this resultant manuscript addresses issues such as patient selection, pre-KD counseling and evaluation, specific dietary therapy selection, implementation, supplementation, follow-up management, adverse event monitoring, and eventual KD discontinuation. This paper highlights recommendations based on best evidence, including areas of agreement and controversy, unanswered questions, and future research.

Clinical aspects of the ketogenic diet

The ketogenic diet remains a valuable therapeutic option for patients with intractable epilepsy. Clinical aspects of the diet's success may provide insights into epileptogenesis and anticonvulsant action. The diet's efficacy has been established primarily through large case series. The diet has been used successfully in patients with many different epilepsy syndromes in countries around the world. Potential adverse effects can be avoided with careful attention during the diet's initiation and maintenance phases. In the last decade, variations to the classical ketogenic diet have been utilized. Ketogenic diets now are being used for diseases other than epilepsy. This critical analysis of the diet should provide the impetus for further clinical and basic research into the diet's application and mechanisms of action.

Muscle phosphofructokinase deficiency with neonatal seizures and nonprogressive course

Muscle phosphofructokinase deficiency is known to cause childhood-onset exercise intolerance, muscle cramps, and myoglobinuria. Rarely, phosphofructokinase deficiency manifests in infancy as congenital myopathy and arthrogryposis with fatal outcome. Here, the authors report the case of a 2-year-old boy with infantile phosphofructokinase deficiency who presented on the third day of life with intractable seizures. Two of his sisters died in infancy with hypotonia, developmental delay, and seizure disorder of unclear etiology. On follow-up, he has had hypotonia and mild developmental delay. However, he continues to gain developmental milestones, and his seizures are now well controlled on carbamazepine. This presentation suggests expanding the phenotype of muscle phosphofructokinase deficiency to include early-onset neonatal seizures. It is also unusual in the relatively milder course of the infantile form of this disorder. The authors propose that this form of glycogen storage disease be considered in the differential diagnosis of neonatal seizures and early infantile nonprogressive muscle weakness.

Floppy infant syndrome

Floppiness/hypotonia is a common neurologic symptom in infancy. A variety of neuromuscular disorders and central nervous system (CNS) disorders cause floppy infant syndrome (FIS). CNS disorders are the much more common causes of the syndrome than neuromuscular disorders. On long-term follow up, cerebral palsy and mental retardation turn out to be the 2 most common causes of FIS. This review focuses on neuromuscular causes of FIS. With the advent of molecular diagnosis, a few conditions can be diagnosed by DNA analysis of the peripheral lymphocytes (myotonic dystrophy, spinal muscular atrophy); however, for the most part, electrodiagnostic studies and muscle biopsy remain as essential diagnostic tools for FIS. Immunohistochemical study of the biopsied muscle also improves diagnostic capability. Management for most conditions remains supportive.

Neuromuscular problems of the critically ill neonate and child

This review presents insights gained over 24 years of clinical and laboratory evaluations of children, newborn to 18 years of age, who present with acute weakness in the intensive care setting. The differential diagnosis of neuromuscular disorders in these cases begins with recognition of three categories-the infant and toddler, the older child and adolescent, and the child with critical illness-within which predisposition to specific disorders may be identified. Disorders originating from anterior horn cell, peripheral nerve, neuromuscular junction, and muscle cell are discussed with emphasis on presentation and electrophysiologic findings. Nerve conduction studies, electromyography, electroencephalography, cerebrospinal fluid analysis, and magnetic resonance imaging each play important diagnostic roles in the differentiation of neuromuscular disorders in the critically ill child. Case studies suggest the wide range of presentations these disorders may make to the pediatrician or pediatric neurologist.

[Ketogenic regime as anti-epileptic treatment: its use in 29 epileptic children]

INTRODUCTION

The ketogenic diet is a treatment option for patient with intractable or refractory epilepsy. It is a high-fat, low protein, low carbohydrate diet developed in 1920s. Recent research publications and media interest have renewed debate on the merits of ketogenic diet.

POPULATION

We report our experience with 29 children suffering from refractory epilepsy, treated with the ketogenic diet. No surgical option was available. Modalities are explained.

RESULTS

The ketogenic diet improved seizure control in 12/29 cases. It appeared effective in infants with infantile spasms. Refractory-status epilepticus responded to the ketogenic diet (3/6 cases). Migrating partial seizures in infancy were always refractory to the diet. Compliance with the diet was good. Adverse effects must be compared with the toxicity of antiepileptic drugs. One child had hypokaliemia with cardiac complication.

CONCLUSION

The ketogenic diet should be continued during one or 2 years when it is effective. It should be considered as an alternative therapy for children with refractory epilepsy.

Muscle glycogenoses

There are 11 hereditary disorders of glycogen metabolism affecting muscle alone or together with other tissues, and they cause two main clinical syndromes: episodic, recurrent exercise intolerance with cramps, myalgia, and myoglobinuria; or fixed, often progressive weakness. Great strides have been made in our understanding of the molecular bases of these disorders, all of which show remarkable genetic heterogeneity. In contrast, the pathophysiological mechanisms underlying acute muscle breakdown and chronic weakness remain unclear. Although glycogen storage diseases have been studied for decades, new biochemical defects are still being discovered, especially in the glycolytic pathway. In addition, the pathogenesis of polyglucosan deposition is being clarified both in traditional glycogenoses and in disorders such as Lafora's disease. In some conditions, combined dietary and exercise regimens may be of help, and gene therapy, including recombinant enzyme replacement, is being actively pursued.

Vagus nerve stimulation and the ketogenic diet

Antiepileptic drugs are the primary form of treatment for patients with epilepsy. In the United States, hundreds of thousands of people do not achieve seizure control, or have significant side effects, or both. Only a minority of patients with intractable epilepsy are candidates for traditional epilepsy surgery. Vagus nerve stimulation is now the second most common treatment for epilepsy in the United States. Additionally, the ketogenic diet has established itself as a valid treatment. This article discusses the history, mechanism of action, patient selection, efficacy, initiation, complications, and advantages of vagus nerve stimulation and the ketogenic diet.

Acute care pediatric electromyography

The recognition of uncommon pediatric motor unit disorders or unusual clinical presentations of common illnesses, such as Guillain-Barré syndrome (GBS), have increased the need for electromyography (EMG) in childhood critical care units. There are two different clinical sets, one appropriate to newborns and infants and the other to older children. Some illnesses that present as an acute floppy infant are not found in the differential diagnosis of motor unit disorders in the older child or adult. These include spinal muscular atrophy, postvaccine poliomyelitis, intrauterine GBS, infantile botulism, and severe myopathies, such as myotonia dystrophy, and some glycogen storage diseases. An appreciation of the neurophysiological maturational norms is essential to an effective pediatric EMG consultation for children ages 0-3 years. Additionally, the neuromuscular complications of extended intubation and sepsis in children are gaining broader recognition. An increased dialogue between clinical neurophysiologists and pediatric neurologists and intensivists in both neonatal and pediatric intensive care units is essential.

Dietary fat, ketosis, and seizure resistance in rats on the ketogenic diet

PURPOSE

Fat is the major component of the ketogenic diet (KD), yet no studies have examined whether the type of fat used in the diet can be optimized to provide additional benefits. The purpose of the present experiments was to compare the efficiency of different fats in inducing ketosis and affording seizure resistance.

METHODS

The effects of KDs that incorporate lard, butter, medium-chain triglycerides (MCT), or flaxseed oil or a mixture of the latter three fats were examined in rats fed KD for up to 98 days. The maximal electroshock (MES) or pentylenetetrazole (PTZ) threshold tests were used to assess seizure susceptibility in two separate experiments.

RESULTS

The rank order of induced ketosis was MCT > mixture > or = flaxseed oil > or = lard = butter > or = control. MES failed to reveal anticonvulsant effects, but the PTZ test indicated that up to 50% of rats fed the KD were seizure protected (p < 0.05). The measures of seizure protection, seizure incidence and score, did not correlate, however, with the level of ketosis in the range of 0. 7-5.2 mmol/L for beta-hydroxybutyrate. In the long-term study, flaxseed oil KD maintained stable ketosis throughout 98 days, whereas ketones declined with lard and butter KD to the control level.

CONCLUSIONS

Seizure protection with the versions of the KD did not improve with the higher level of ketosis. The focus of the KD improvement, therefore, is not the achievement of higher ketosis per se but rather designing a diet that provides steady ketosis, exploits advantages of certain fats for neurological development or seizure protection via a nonketogenic mechanism, and is nutritionally balanced.

Diagnosis of pediatric neuromuscular disorders in the era of DNA analysis

Extraordinary breakthroughs in the molecular pathogenesis of muscle and nerve disease have resulted in an evolving genetic classification of neuromuscular disorders and the development of new diagnostic methods. This remarkable progress has introduced new genetic tests and has changed the indications for use of certain invasive diagnostic procedures in the evaluation of children with presumed disorders of the motor unit. In this review, we present the current diagnostic approach to the more common neuromuscular diseases of infancy and childhood and define the diagnostic role of muscle biopsy and pediatric electromyography/nerve conduction studies in the era of genetic analysis.

Other erythrocyte enzyme deficiencies associated with non-haematological symptoms: phosphoglycerate kinase and phosphofructokinase deficiency

Phosphoglycerate kinase (PGK) deficiency is associated with hereditary haemolytic anaemia and often with central nervous system dysfunction and/or myopathy. Twenty-three families have been discovered with this condition. Nine have manifested both symptoms, six only haemolysis, and seven central nervous system dysfunction and/or myopathy without haemolysis; one case is asymptomatic. Among them, the structural abnormalities of 14 mutants, including 11 missense mutations, 1 gene deletion, 1 gene insertion, and 1 splicing mutation, have been identified. The correlation between the phenotypic and structural differences in PGK deficiency remains to be defined. Splenectomy obviates transfusion in most patients but does not correct the haemolytic disorder. Phosphofructokinase (PFK) deficiency is associated with myopathy and/or haemolysis. More than half reported had the typical features of glycogen storage disease type VII (Tarui disease). The other cases exhibited myopathy alone, haemolytic anaemia alone, or no clinical symptom at all. Eight missense, 1 nonsense, 1 frameshift and 5 splicing mutations have been determined in the PFK-M gene. In classic PFK-M deficiency, the avoidance of undue exertion is the key to prevent muscle symptoms.

Metabolic myopathies: a clinical approach; part II

Major recent advances in the field of metabolic myopathies have helped delineate the genetic and biochemical basis of these disorders. This progress has also resulted in the development of new diagnostic and therapeutic methodologies. In this second part, we present an updated review of the main nonlysosomal and lysosomal glycogenoses and lipid metabolism defects that manifest with signs of transient or permanent muscle dysfunction. Our intent is to increase the pediatric neurologist's familiarity with these conditions and thus improve decision making in the areas of diagnosis and treatment.

Glycogen storage myopathies

The glycogen storage myopathies are caused by enzyme defects in the glycogenolytic or in the glycolytic pathway affecting skeletal muscle alone or in conjunction with other tissues. The authors review recent findings in this area, including a new entity, aldolase deficiency, and the wealth of molecular genetic data that are rapidly accumulating. Despite this progress, genotype-phenotyp3 correlations are still murky in most glycogen storage myopathies.

The molecular diagnosis of metabolic myopathies

The metabolic myopathies are distinguished by extensive clinical and genetic heterogeneity within and between individual disorders. There are a number of explanations for the variability observed that go beyond single gene mutations or degrees of heteroplasmy in the case of mitochondrial DNA mutations. Some of the contributing factors include protein subunit interactions, tissue-specificity, modifying genetic factors, and environmental triggers. Advances in the molecular analysis of metabolic myopathies during the last decade have not only improved the diagnosis of individual disorders but also helped to characterize the contributing factors that make these disorders so complex.

Metabolic and endocrine aspects of the ketogenic diet

The ketogenic diet (KD) is designed to simulate the biochemical effects of fasting by maintaining a state of ketosis. The complex interplay of endocrine and metabolic factors requires that a continuous ingestion of a diet high in lipid calories is necessary to achieve such a state and yet maintain body weight. The resulting condition provides for much of the cerebral energy requirements in the form of ketone bodies. We review energy metabolism with special emphasis on fatty acid oxidation to provide the readers with a foundation that facilitates identification of patients who will especially benefit from this diet, as well as to assist clinicians in screening candidates who may experience a catastrophic outcome if fasted and placed on this diet. The review includes a discussion of the role of carnitine in mitochondrial fatty acid metabolism, and the criteria for carnitine supplementation. Only limited information is available regarding the interaction of the diet with the commonly used antiepileptic drugs.

Glycogen storage diseases of muscle

Ten specific enzyme defects of glycogen metabolism affect skeletal muscle alone or in combination with other tissues. The newest addition to this group of disorders is the defect of aldolase A (glycogenosis type XII), a block in terminal glycolysis associated with myopathy and a hemolytic trait. The muscle glycogenoses cause two major syndromes, one characterized by exercise intolerance, cramps, and myoglobinuria, and the other dominated by fixed, often progressive weakness. This review considers sequentially recent advances in the following: clinical features or clinical variants, including a brief description of glycogenosis type XII; animal models, both spontaneous and genetically engineered; physiopathologic mechanisms, especially of the exercise intolerance and myoglobinuria; biochemical and molecular features--molecular defects are just beginning to be discovered for some glycogenoses (e.g. phosphorylase-b-kinase deficiency or branching enzyme deficiency), whereas they form long lists for others, such as acid maltase deficiency and myophosphorylase deficiency; and therapeutic approaches, including enzyme replacement and gene therapy.