Paediatric single mitochondrial DNA deletion disorders: an overlapping spectrum of disease.

BACKGROUND: Single large-scale mitochondrial DNA (mtDNA) deletions (SLSMDs) are amongst the most frequently diagnosed mtDNA disorders in childhood, yet their natural history remains poorly understood. We report the natural history of a large multicentre cohort of such children. METHODS: We reviewed case notes from three different UK centres to determine the clinical course of 34 patients (16 female, 18 male) with childhood-onset mitochondrial disease caused by SLSMDs. Kaplan-Meier analysis was used to compare survival of patients presenting with haematological features (Pearson syndrome) and those with nonhaematological presentations. RESULTS: The most frequent initial presentation was with isolated ptosis (16/34, 47%). Eleven (32%) patients presented with transfusion-dependent anaemia soon after birth and were diagnosed with Pearson syndrome, whilst ten were classified as having Kearns-Sayre syndrome, three as having progressive external ophthalmoplegia (PEO) and seven as having PEO-plus. Three patients did not conform to any specific mitochondrial syndrome. The most frequently affected organ during the disease course was the kidney, with documented tubular or glomerular dysfunction in 17 of 20 (85%) cases who had detailed investigations. SLSMDs were present in blood and/or urine cells in all cases tested, indicating that muscle biopsy is not necessary for diagnosis in the paediatric age range. Kaplan-Meier survival analysis revealed significantly worse mortality in patients with Pearson syndrome compared with the rest of the cohort. CONCLUSIONS: Mitochondrial disease caused by SLSMDs is clinically heterogeneous, and not all cases conform to a classical mitochondrial syndrome. Multisystem disease is the norm, with anaemia, renal impairment and endocrine disturbance being the most frequent extraneurological features. SLSMDs should be considered in the differential diagnosis of all children presenting with ptosis.

Plasma thiol status is altered in children with mitochondrial diseases.

OBJECTIVE: This study was undertaken to investigate thiol metabolism as a marker of oxidative stress and antioxidative defence capacity in a cohort of children with biochemically and/or genetically confirmed mitochondrial disease. Previous studies suggest that lower glutathione levels, which have been shown to further compromise mitochondrial function, may occur in these diseases. Better understanding of the pathogenesis of mitochondrial diseases is important in order to improve their treatment. METHODS: We studied plasma and erythrocyte glutathione and cysteine levels, the activities of erythrocyte glutathione peroxidase (GPx), glutathione reductase (GR), glucose 6-phosphate dehydrogenase G6PDH) and glutathione S-transferase (GST), as well as the levels of erythrocyte thiobarbituric acid-reactive species (TBA-RS) and protein carbonyls in 10 children with a biochemical and/or genetic diagnosis of mitochondrial disease and six controls. RESULTS: Levels of reduced cysteine (CYSH) as well as reduced to oxidised cysteine ratio were lower in plasma of patients with mitochondrial diseases (p = 0.008 and p = 0.02, respectively). Plasma levels of reduced glutathione (GSH) were low in patients with mitochondrial diseases, mostly below the detection limit. We did not detect significant differences in erythrocyte thiols or glutathione-related enzyme activities. CONCLUSION: Plasma thiols and their redox state are altered in patients with mitochondrial diseases, suggesting an increase in oxidative stress and depletion of antioxidant supplies. If confirmed in further studies, this relative thiol deficiency could be an important factor in the pathophysiology of mitochondrial diseases.

Patients with organic acidaemias have an altered thiol status.

AIM: To study whether patients with organic acidaemias have altered glutathione (GSH) levels and thiol redox status. Previously, organic acidaemias have been associated with mitochondrial dysfunction and oxidative stress, suggesting an increased need for antioxidant protection. Furthermore, dietary protein restriction may impair GSH synthesis in these diseases. METHODS: In children with organic acidaemias, cysteine (CYSH) and GSH concentrations in plasma and erythrocytes as well as erythrocyte GSH peroxidase, GSH reductase, GSH S-transferase and glucose-6-phosphate dehydrogenase activities were studied. In addition, GSH and CYSH concentrations were measured in human fibroblasts exposed to organic acids. RESULTS: Patients with organic acidaemias had lower plasma GSH concentration than their controls. A greater fraction of GSH and CYSH in the patients' plasma was oxidized, suggesting decreased GSH synthesis and increased consumption. CONCLUSION: Patients with organic acidaemias may have a relative GSH deficiency. With further research, these results could also have therapeutic implications.

Diagnosis and management of glutaric aciduria type I--revised recommendations.

Glutaric aciduria type I (synonym, glutaric acidemia type I) is a rare organic aciduria. Untreated patients characteristically develop dystonia during infancy resulting in a high morbidity and mortality. The neuropathological correlate is striatal injury which results from encephalopathic crises precipitated by infectious diseases, immunizations and surgery during a finite period of brain development, or develops insidiously without clinically apparent crises. Glutaric aciduria type I is caused by inherited deficiency of glutaryl-CoA dehydrogenase which is involved in the catabolic pathways of L-lysine, L-hydroxylysine and L-tryptophan. This defect gives rise to elevated glutaric acid, 3-hydroxyglutaric acid, glutaconic acid, and glutarylcarnitine which can be detected by gas chromatography/mass spectrometry (organic acids) or tandem mass spectrometry (acylcarnitines). Glutaric aciduria type I is included in the panel of diseases that are identified by expanded newborn screening in some countries. It has been shown that in the majority of neonatally diagnosed patients striatal injury can be prevented by combined metabolic treatment. Metabolic treatment that includes a low lysine diet, carnitine supplementation and intensified emergency treatment during acute episodes of intercurrent illness should be introduced and monitored by an experienced interdisciplinary team. However, initiation of treatment after the onset of symptoms is generally not effective in preventing permanent damage. Secondary dystonia is often difficult to treat, and the efficacy of available drugs cannot be predicted precisely in individual patients. The major aim of this revision is to re-evaluate the previous diagnostic and therapeutic recommendations for patients with this disease and incorporate new research findings into the guideline.

A lethal defect of mitochondrial and peroxisomal fission.

We report on a newborn girl with microcephaly, abnormal brain development, optic atrophy and hypoplasia, persistent lactic acidemia, and a mildly elevated plasma concentration of very-long-chain fatty acids. We found a defect of the fission of both mitochondria and peroxisomes, as well as a heterozygous, dominant-negative mutation in the dynamin-like protein 1 gene (DLP1). The DLP1 protein has previously been implicated, in vitro, in the fission of both these organelles. Overexpression of the mutant DLP1 in control cells reproduced the fission defect. Our findings are representative of a class of disease characterized by defects in both mitochondria and peroxisomes.

Analysis of mutant DNA polymerase gamma in patients with mitochondrial DNA depletion.

We studied six unrelated children with depletion of mitochondrial DNA (mtDNA). They presented with Leigh syndrome, infantile hepatocerebral mtDNA depletion syndrome, or Alpers-Huttenlocher syndrome. Several genes have been implicated in mtDNA depletion. Screening of candidate genes indicated that all six patients were compound heterozygous for missense mutations in the gene for the catalytic subunit of DNA polymerase gamma (POLG). Three of the identified mutations, c.3328C>T (p.H1110Y), c.3401A>G (p.H1134R), and c.3406G>A (p.E1136K), have not been reported earlier. To investigate the functional consequences of the mutations, we carried out a series of biochemical assays in cultured fibroblasts. These studies revealed that fibroblast cultures from the patients with infantile hepatocerebral mtDNA depletion syndrome progressively lost their mtDNA during culturing, whereas fibroblast cultures from patients presenting with Leigh syndrome or Alpers-Huttenlocher syndrome had reduced but stable levels of mtDNA. DNA polymerase gamma activity was below the normal range in all patient cultures, except for one; however, this culture showed low levels of the heterodimeric enzyme and poor DNA polymerase gamma processivity. Parental fibroblast cultures had normal catalytic efficiency of DNA polymerase gamma, consistent with the observation that all carriers are asymptomatic. Thus, we report the first patient with Leigh syndrome caused by POLG mutations. The cell culture experiments established the pathogenicity of the identified POLG mutations and helped to define the molecular mechanisms responsible for mtDNA depletion in the patients' tissues. The assays may facilitate the identification of those patients in whom screening for POLG mutations would be most appropriate.

Utilization of cornstarch in glycogen storage disease type Ia.

OBJECTIVE: Uncooked cornstarch (UCCS) is used widely for the treatment of patients with glycogen storage disease type I (GSD-I). Previous studies suggested that glucose absorption may be impaired in GSD-I. In order to measure utilization of UCCS in young adults with GSD-Ia and healthy controls, we used a C-breath test based on the natural enrichment of C in UCCS. DESIGN: Open, not randomized, prospective interventional study. METHODS: Following 1 g/kg UCCS, we studied eight subjects with GSD-Ia (7 males, 1 female; mean age 28.3 years, range 16-42 years) and 15 healthy controls (10 males, 5 females; mean age 23.5 years, range 19-36 years). Breath samples for analysis of CO enrichment were collected at baseline and at 30-min intervals for 6 h or until hypoglycaemia occurred. Indirect calorimetry was used to measure respiratory gas exchange. Intermediate metabolites, lipids and glucose were measured in plasma. Breath H concentrations were measured as an indicator of malabsorption. RESULTS: Cumulative utilization over 6 h was significantly higher in controls (18.35 +/- 6.2% of total carbohydrate intake) than in subjects with GSD-Ia (11.5 +/- 4.7%) (P < 0.02). However, utilization of UCCS was virtually identical up to 2.5 h. Two subjects with GSD-Ia fulfilled the criteria for malabsorption. CONCLUSIONS: Starch digestion and absorption are not impaired in GSD-Ia. However, overall utilization of UCCS appears to be lower in GSD-Ia, which is most likely secondary to perturbed intermediary metabolism. There are important implications for treatment of this disorder. Ways to improve the efficacy of UCCS in GSD-I are needed.

Recommendations for the management of tyrosinaemia type 1.

The management of tyrosinaemia type 1 (HT1, fumarylacetoacetase deficiency) has been revolutionised by the introduction of nitisinone but dietary treatment remains essential and the management is not easy. In this review detailed recommendations for the management are made based on expert opinion, published case reports and investigational studies as the evidence base is limited and there are no prospective controlled studies.The added value of this paper is that it summarises in detail current clinical knowledge about HT1 and makes recommendations for the management.

HIBCH mutations can cause Leigh-like disease with combined deficiency of multiple mitochondrial respiratory chain enzymes and pyruvate dehydrogenase.

BACKGROUND: Deficiency of 3-hydroxy-isobutyryl-CoA hydrolase (HIBCH) caused by HIBCH mutations is a rare cerebral organic aciduria caused by disturbance of valine catabolism. Multiple mitochondrial respiratory chain (RC) enzyme deficiencies can arise from a number of mechanisms, including defective maintenance or expression of mitochondrial DNA. Impaired biosynthesis of iron-sulphur clusters and lipoic acid can lead to pyruvate dehydrogenase complex (PDHc) deficiency in addition to multiple RC deficiencies, known as the multiple mitochondrial dysfunctions syndrome. METHODS: Two brothers born to distantly related Pakistani parents presenting in early infancy with a progressive neurodegenerative disorder, associated with basal ganglia changes on brain magnetic resonance imaging, were investigated for suspected Leigh-like mitochondrial disease. The index case had deficiencies of multiple RC enzymes and PDHc in skeletal muscle and fibroblasts respectively, but these were normal in his younger brother. The observation of persistently elevated hydroxy-C4-carnitine levels in the younger brother led to suspicion of HIBCH deficiency, which was investigated by biochemical assay in cultured skin fibroblasts and molecular genetic analysis. RESULTS: Specific spectrophotometric enzyme assay revealed HIBCH activity to be below detectable limits in cultured skin fibroblasts from both brothers. Direct Sanger sequence analysis demonstrated a novel homozygous pathogenic missense mutation c.950G

Diagnosis and early management of inborn errors of metabolism presenting around the time of birth.

UNLABELLED: Inherited metabolic diseases often present around the time of birth. They are responsible for some cases of hydrops fetalis and a number of dysmorphic syndromes. Patients with inborn errors may also present at (or shortly after) birth with seizures or severe hypotonia. Most affected babies, however, appear normal at birth and subsequently deteriorate, with hypoglycaemia, acidosis, neurological or cardiac problems, or liver disease. Treatment often involves measures to reduce catabolism and to remove toxic metabolites. It should not be delayed for a definitive diagnosis. CONCLUSION: In the newborn period, inborn errors can easily be misdiagnosed as sepsis or birth asphyxia; prompt detection requires vigilance and the early measurement of biochemical markers, such as plasma ammonia.

Phenotypic variability of mitochondrial disease caused by a nuclear mutation in complex II.

We report a patient with relatively mild Leigh syndrome and mitochondrial respiratory chain complex II deficiency caused by a homozygous G555E mutation in the nuclear encoded flavoprotein subunit of succinate dehydrogenase. This mutation has previously been reported in a lethal-infantile presentation of complex II deficiency. Such marked phenotypic heterogeneity, although typical of heteroplasmic mutations in the mitochondrial genome, is unusual for nuclear mutations. Comparable activities and stability of mitochondrial respiratory chain enzymes were demonstrated in both patients, so other reasons for the phenotypic variability are considered.

Natural history, outcome, and treatment efficacy in children and adults with glutaryl-CoA dehydrogenase deficiency.

Glutaryl-CoA dehydrogenase (GCDH) deficiency is a rare inborn disorder of L-lysine, L-hydroxylysine, and L-tryptophan metabolism complicated by striatal damage during acute encephalopathic crises. Three decades after its description, the natural history and how to treat this disorder are still incompletely understood. To study which variables influenced the outcome, we conducted an international cross-sectional study in 35 metabolic centers. Our main outcome measures were onset and neurologic sequelae of acute encephalopathic crises. A total of 279 patients (160 male, 119 female) were included who were diagnosed clinically after clinical presentation (n = 218) or presymptomatically by neonatal screening (n = 23), high-risk screening (n = 24), or macrocephaly (n = 14). Most symptomatic patients (n = 185) had encephalopathic crises, characteristically resulting in bilateral striatal damage and dystonia, secondary complications, and reduced life expectancy. First crises usually occurred during infancy (95% by age 2 y); the oldest age at which a repeat crisis was reported was 70 mo. In a few patients, neurologic disease developed without a reported crisis. Differences in the diagnostic criteria and therapeutic protocols for patients with GCDH deficiency resulted in a huge variability in the outcome worldwide. Recursive partitioning demonstrated that timely diagnosis in neurologically asymptomatic patients followed by treatment with L-carnitine and a lysine-restricted diet was the best predictor of good outcome, whereas treatment efficacy was low in patients diagnosed after the onset of neurologic disease. Notably, the biochemical phenotype did not predict the clinical phenotype. Our study proves GCDH deficiency to be a treatable disorder and a good candidate for neonatal screening.

The role of liver transplantation in urea cycle disorders.

Liver transplantation has an important role in the management of patients with urea cycle disorders, particularly those with severe variants, progressive liver disease, and some patients who have proved very difficult to control with conventional therapy. As a result of technical advances in liver transplantation, the outlook, both morbidity and mortality, is better and continues to improve. Patients can almost always have a normal diet and the quality of life for survivors is generally excellent.

The impact of screening for propionic and methylmalonic acidaemia.

UNLABELLED: The outcome of the severe variants of propionic and methylmalonic acidaemia is not good. Patients with these disorders have increased concentrations of propionylcarnitine and using tandem mass spectrometry to detect this compound, it is possible to screen in the newborn period. Various criteria have been used to identify the patients but only a small number of patients have been diagnosed so far and some have been missed. Furthermore many will have already presented before the result of the screening test is available. CONCLUSION: It is not yet clear whether the outcome is better for those identified in screening programmes.

Nephrocalcinosis and medullary cysts in 3-methylglutaconic aciduria.

3-methylglutaconic aciduria is frequently found during urine organic acid analysis and is widely regarded as a marker of a mitochondrial disorder, the clinical features of which are very heterogeneous. We describe two siblings with 3-methylglutaconic aciduria in whom renal ultrasonography showed echogenic medullae consistent with nephrocalcinosis. One patient also developed medullary cysts. In both children renal function was normal and neither had any plasma or urinary evidence of tubulopathy. The presence of nephrocalcinosis and medullary cysts in patients with 3-methylglutaconic aciduria adds to the heterogeneous clinical presentation of this group of disorders.

The regulation of growth in glycogen storage disease type 1.

OBJECTIVE: To study endocrine and metabolic variables that affect growth in patients with glycogen storage disease type 1 (GSD-1) receiving standard dietary therapy. DESIGN: Observational study. PATIENTS AND MEASUREMENTS: Thirty-eight patients with GSD-1, age range 0.6-32.9 years, were investigated on their usual dietary regimens. Data on height, height velocity in prepubertal children, endocrine and metabolic responses to oral glucose load, 24-h serum cortisol and GH concentration profiles and serum IGF-1 concentrations were collected. RESULTS: The population studied was shorter than average, with a median height standard deviation score (SDS) of -1.60, but significantly taller than a historical population studied at the same institution that had not received dietary therapy at the time of study. A wide range of height SDS was encountered (-5.28 to 1.21) and a subset still exhibit marked growth failure. Median body mass index (BMI) SDS was 0.72 (range -1.34 to 3.96). Those patients with the greatest BMI SDS had the lowest serum GH concentrations but serum IGF-1 concentrations were within the normal range. Patients with the poorest growth exhibit low serum insulin concentration responses to glucose load, GH insensitivity and higher mean 24-h plasma cortisol levels when compared to those patients who were better grown. CONCLUSION: This study shows that overall the growth of this group of patients with glycogen storage disease type 1 has improved compared to that of a historical control group. There remains a subset of this population with poor growth despite therapy. The measured endocrine responses in this subset are similar to those reported for untreated patients. To improve the growth further in these individuals it will be necessary to understand whether this is failure of prescribed therapy or failure to comply with therapy.

Mutations in the gene for the E1beta subunit: a novel cause of pyruvate dehydrogenase deficiency.

We describe two unrelated patients with pyruvate dehydrogenase (PDH) deficiency attributable to mutations in the gene encoding the E1beta subunit of the complex. This is a previously unrecognised form of PDH deficiency, which most commonly results from mutations in the X-linked gene for the E1alpha subunit. Both patients had reduced immunoreactive E1beta protein and both had missense mutations in the E1beta gene. Activity of the PDH complex was restored in cultured fibroblasts from both patients by transfection and expression of the normal E1beta coding sequence.

Glycogen storage disease type I: diagnosis, management, clinical course and outcome. Results of the European Study on Glycogen Storage Disease Type I (ESGSD I).

UNLABELLED: Glycogen storage disease type I (GSD I) is a relatively rare metabolic disease and therefore, no metabolic centre has experience of large numbers of patients. To document outcome, to develop guidelines about (long-term) management and follow-up, and to develop therapeutic strategies, the collaborative European Study on GSD I (ESGSD I) was initiated. This paper is a descriptive analysis of data obtained from the retrospective part of the ESGSD I. Included were 231 GSD Ia and 57 GSD Ib patients. Median age of data collection was 10.4 years (range 0.4-45.4 years) for Ia and 7.1 years (0.4-30.6 years) for Ib patients. Data on dietary treatment, pharmacological treatment, and outcome including mental development, hyperlipidaemia and its complications, hyperuricaemia and its complications, bleeding tendency, anaemia, osteopenia, hepatomegaly, liver adenomas and carcinomas, progressive renal disease, height and adult height, pubertal development and bone maturation, school type, employment, and pregnancies are presented. Data on neutropenia, neutrophil dysfunction, infections, inflammatory bowel disease, and the use of granulocyte colony-stimulating factor are presented elsewhere (Visser et al. 2000, J Pediatr 137:187-191; Visser et al. 2002, Eur J Pediatr DOI 10.1007/s00431-002-1010-0). CONCLUSION: there is still wide variation in methods of dietary and pharmacological treatment of glycogen storage disease type I. Intensive dietary treatment will improve, but not correct completely, clinical and biochemical status and fewer patients will die as a direct consequence of acute metabolic derangement. With ageing, more and more complications will develop of which progressive renal disease and the complications related to liver adenomas are likely to be two major causes of morbidity and mortality.

Guidelines for management of glycogen storage disease type I - European Study on Glycogen Storage Disease Type I (ESGSD I).

UNLABELLED: Life-expectancy in glycogen storage disease type I (GSD I) has improved considerably. Its relative rarity implies that no metabolic centre has experience of large series of patients and experience with long-term management and follow-up at each centre is limited. There is wide variation in methods of dietary and pharmacological treatment. Based on the data of the European Study on Glycogen Storage Disease Type I, discussions within this study group, discussions with the participants of the international SHS-symposium 'Glycogen Storage Disease Type I and II: Recent Developments, Management and Outcome' (Fulda, Germany; 22-25th November 2000) and on data from the literature, guidelines are presented concerning: (1). diagnosis, prenatal diagnosis and carrier detection; (2). (biomedical) targets; (3). recommendations for dietary treatment; (4). recommendations for pharmacological treatment; (5). metabolic derangement/intercurrent infections/emergency treatment/preparation elective surgery; and (6). management of complications (directly) related to metabolic disturbances and complications which may develop with ageing and their follow-up. CONCLUSION: In this paper guidelines for the management of GSD I are presented.