Phenotypic spectrum and clinical course of single large-scale mitochondrial DNA deletion disease in the paediatric population: a multicentre study.

BACKGROUND: Large-scale mitochondrial DNA deletions (LMD) are a common genetic cause of mitochondrial disease and give rise to a wide range of clinical features. Lack of longitudinal data means the natural history remains unclear. This study was undertaken to describe the clinical spectrum in a large cohort of patients with paediatric disease onset. METHODS: A retrospective multicentre study was performed in patients with clinical onset <16 years of age, diagnosed and followed in seven European mitochondrial disease centres. RESULTS: A total of 80 patients were included. The average age at disease onset and at last examination was 10 and 31 years, respectively. The median time from disease onset to death was 11.5 years. Pearson syndrome was present in 21%, Kearns-Sayre syndrome spectrum disorder in 50% and progressive external ophthalmoplegia in 29% of patients. Haematological abnormalities were the hallmark of the disease in preschool children, while the most common presentations in older patients were ptosis and external ophthalmoplegia. Skeletal muscle involvement was found in 65% and exercise intolerance in 25% of the patients. Central nervous system involvement was frequent, with variable presence of ataxia (40%), cognitive involvement (36%) and stroke-like episodes (9%). Other common features were pigmentary retinopathy (46%), short stature (42%), hearing impairment (39%), cardiac disease (39%), diabetes mellitus (25%) and renal disease (19%). CONCLUSION: Our study provides new insights into the phenotypic spectrum of childhood-onset, LMD-associated syndromes. We found a wider spectrum of more prevalent multisystem involvement compared with previous studies, most likely related to a longer time of follow-up.

Clinical and demographic features of chronic progressive external ophthalmoplegia in a large adult-onset cohort.

Chronic progressive external ophthalmoplegia (CPEO) is a common mitochondrial disease. We evaluated the impact of sex and smoking status upon knee extension strength and the phenotypic spectrum of disease in a large cohort of adult-onset CPEO patients (N=116) using retrospective chart analysis. The CPEO patients showed significantly lower knee extension strength as compared to the age- and sex-matched control population (-37%, P<0.05). Smoking also negatively impacted knee extension strength only in women with CPEO (-26%, P<0.05). We conclude that smoking and female sex interact negatively in CPEO patients.

Relapsing remitting multiple sclerosis in progressive external ophthalmoplegia: A report of two cases.

Evidence from genetic and pathologic studies suggests that mitochondrial dysfunction occurs in multiple sclerosis (MS). Furthermore, cases of MS have been reported in patients with mitochondrial disease. The phenotypic range of mitochondrial illness associating with MS is not yet well defined. In this report, we highlight two cases of patients with confirmed genetic mutations responsible for progressive external ophthalmoplegia who independently meet McDonald criteria for MS. Better characterization of the range of mitochondrial disease associated with MS may improve our understanding of MS disease pathophysiology.

Ophthalmoplegia in Mitochondrial Disease.

PURPOSE: To evaluate the classification, diagnosis, and natural course of ophthalmoplegia associated with mitochondrial disease. MATERIALS AND METHODS: Among 372 patients with mitochondrial disease who visited our hospital between January 2006 and January 2016, 21 patients with ophthalmoplegia were retrospectively identified. Inclusion criteria included onset before 20 years of age, pigmentary retinopathy, and cardiac involvement. The 16 patients who were finally included in the study were divided into three groups according to disease type: Kearns-Sayre syndrome (KSS), KSS-like, and chronic progressive external ophthalmoplegia (CPEO). RESULTS: The prevalences of clinical findings were as follows: ptosis and retinopathy, both over 80%; myopathy, including extraocular muscles, 75%; lactic acidosis, 71%; and elevated levels of serum creatine kinase, 47%. Half of the patients had normal magnetic resonance imaging findings. A biochemical enzyme assay revealed mitochondrial respiratory chain complex I defect as the most common (50%). The prevalence of abnormal muscle findings in light or electron microscopic examinations was 50% each, while that of large-scale mitochondrial DNA (mtDNA) deletions in a gene study was 25%. We compared the KSS and KSS-like groups with the CPEO patient group, which showed pigmentary retinopathy (p<0.001), cardiac conduction disease (p=0.013), and large-scale mtDNA deletions (p=0.038). KSS and KSS-like groups also had gastrointestinal tract disorders such as abnormal gastrointestinal motility (p=0.013) unlike the CPEO group. CONCLUSION: Patients with KSS had gastrointestinal symptoms, which may indicate another aspect of systemic involvement. The presence of large-scale mtDNA deletions was an objective diagnostic factor for KSS and a gene study may be helpful for evaluating patients with KSS.

Revisiting mitochondrial ocular myopathies: a study from the Italian Network.

Ocular myopathy, typically manifesting as progressive external ophthalmoplegia (PEO), is among the most common mitochondrial phenotypes. The purpose of this study is to better define the clinical phenotypes associated with ocular myopathy. This is a retrospective study on a large cohort from the database of the "Nation-wide Italian Collaborative Network of Mitochondrial Diseases". We distinguished patients with ocular myopathy as part of a multisystem mitochondrial encephalomyopathy (PEO-encephalomyopathy), and then PEO with isolated ocular myopathy from PEO-plus when PEO was associated with additional features of multisystemic involvement. Ocular myopathy was the most common feature in our cohort of mitochondrial patients. Among the 722 patients with a definite genetic diagnosis, ocular myopathy was observed in 399 subjects (55.3%) and was positively associated with mtDNA single deletions and POLG mutations. Ocular myopathy as manifestation of a multisystem mitochondrial encephalomyopathy (PEO-encephalomyopathy, n = 131) was linked to the m.3243A>G mutation, whereas the other "PEO" patients (n = 268) were associated with mtDNA single deletion and Twinkle mutations. Increased lactate was associated with central neurological involvement. We then defined, among the PEO group, as "pure PEO" the patients with isolated ocular myopathy and "PEO-plus" those with ocular myopathy and other features of neuromuscular and multisystem involvement, excluding central nervous system. The male proportion was significantly lower in pure PEO than PEO-plus. This study reinforces the need for research on the role of gender in mitochondrial diseases. The phenotype definitions here revisited may contribute to a more homogeneous patient categorization, useful in future studies and clinical trials.

SANDO syndrome in a cohort of 107 patients with CPEO and mitochondrial DNA deletions.

OBJECTIVE: The sensory ataxic neuropathy with dysarthria and ophthalmoparesis (SANDO) syndrome is a subgroup of mitochondrial chronic progressive external ophthalmoplegia (CPEO)-plus disorders associated with multiple mitochondrial DNA (mtDNA) deletions. There is no systematic survey on SANDO in patients with CPEO with either single or multiple large-scale mtDNA deletions. METHODS: In this retrospective analysis, we characterised the frequency, the genetic and clinical phenotype of 107 index patients with mitochondrial CPEO (n=66 patients with single and n=41 patients with multiple mtDNA deletions) and assessed these for clinical evidence of a SANDO phenotype. Patients with multiple mtDNA deletions were additionally screened for mutations in the nuclear-encoded POLG, SLC25A4, PEO1 and RRM2B genes. The clinical, histological and genetic data of 11 patients with SANDO were further analysed. RESULTS: None of the 66 patients with single, large-scale mtDNA deletions fulfilled the clinical criteria of SANDO syndrome. In contrast, 9 of 41 patients (22%) with multiple mtDNA deletions and two additional family members fulfilled the clinical criteria for SANDO. Within this subgroup, multiple mtDNA deletions were associated with the following nuclear mutations: POLG (n=6), PEO1 (n=2), unidentified (n=2). The combination of sensory ataxic neuropathy with ophthalmoparesis (SANO) was observed in 70% of patients with multiple mtDNA deletions but only in 4% with single deletions. The combination of CPEO and sensory ataxic neuropathy (SANO, incomplete SANDO) was found in 43% of patients with multiple mtDNA deletions but not in patients with single deletions. CONCLUSION: The SANDO syndrome seems to indicate a cluster of symptoms within the wide range of multisystemic symptoms associated with mitochondrial CPEO. SANO seems to be the most frequent phenotype associated with multiple mtDNA deletions in our cohort but not or is rarely associated with single, large-scale mtDNA deletions.

Characteristics of intestinal pseudo-obstruction in patients with mitochondrial diseases.

AIM: To reveal the frequency, characteristics and prognosis of chronic intestinal pseudo-obstruction (CIP) in mitochondrial disease patients. METHODS: Between January 2000 and December 2010, 31 patients (13 males and 18 females) were diagnosed with mitochondrial diseases at our hospital. We conducted a retrospective review of the patients' sex, subclass of mitochondrial disease, age at onset of mitochondrial disease, frequency of CIP and the age at its onset, and the duration of survival. The age at onset or at the first diagnosis of the disorder that led to the clinical suspicion of mitochondrial disease was also examined. RESULTS: Twenty patients were sub-classified with mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS), 8 with chronic progressive external ophthalmoplegia (CPEO), and 3 with myoclonus epilepsy associated with ragged-red fibers (MERRF). Nine patients were diagnosed with CIP, 8 of the 20 (40.0%) patients with MELAS, 0 of the 8 (0.0%) patients with CPEO, and 1 of the 3 (33.3%) patients with MERRF. The median age (range) at the diagnosis and the median age at onset of mitochondrial disease were 40 (17-69) and 25 (12-63) years in patients with CIP, and 49 (17-81) and 40 (11-71) years in patients without CIP. During the survey period, 5 patients (4 patients with MELAS and 1 with CPEO) died. The cause of death was cardiomyopathy in 2 patients with MELAS, cerebral infarction in 1 patient with MELAS, epilepsy and aspiration pneumonia in 1 patient with MELAS, and multiple metastases from gastric cancer and aspiration pneumonia in 1 patient with CPEO. CONCLUSION: Patients with CIP tend to have disorders that are suspected to be related to mitochondrial diseases at younger ages than are patients without CIP.

Progressive external ophthalmoplegia in southwestern Finland: a clinical and genetic study.

BACKGROUND: Progressive external ophthalmoplegia (PEO) is a common phenotype of mitochondrial disease. Molecular etiologies include sporadic, large-scale deletions in mitochondrial DNA (mtDNA), multiple mtDNA deletions secondary to autosomal dominant or recessive mutations and mtDNA point mutations. METHODS: We studied the prevalence and clinical and genetic characteristics of PEO in a defined population in southwestern Finland. A total of 620 patients were first identified from the patient registry at the Turku University Hospital over an 18-year period. The medical records of these patients were scrutinized, and those with clinical features compatible with PEO were ascertained. RESULTS: We identified 10 patients with possible PEO. The patients were examined clinically, and DNA was analyzed for mtDNA deletions and for the m.3243A>G and m.8344A>G mtDNA point mutations. The ANT1, PEO1, POLG1 and POLG2 genes were sequenced. We confirmed the clinical diagnosis of PEO in 6 patients. Large-scale mtDNA deletions were detected in 3 out of 6 PEO patients and mutations in the POLG1 gene in 1 out of 6. We did not find any mutations in the ANT1, PEO1 or POLG2 genes. CONCLUSIONS: Our results suggest that molecular investigation of patients with PEO, either sporadic or familial, should start with an analysis for mtDNA deletions, followed by an analysis of the POLG1 gene.

Multisystem disorder in late-onset chronic progressive external ophthalmoplegia.

INTRODUCTION: Chronic progressive external ophthalmoplegia (CPEO) is a mitochondrial syndrome on a disease spectrum with Kearns-Sayre syndrome (KSS). Clinical presentation is variable and our experience suggested that phenotypic differences exist in CPEO with onset after age 20. METHODS: This descriptive study is a retrospective chart review of 40 patients with late-onset CPEO. Clinical features, laboratory and neurophysiology results were reviewed. RESULTS: Multisystem dysfunction was very common in this series. Gastrointestinal dysfunction was more common than expected (60%) as was migraine headache (40%). Clinical characteristics on the KSS disease spectrum were uncommon in this series with only 2.5% having pigmentary retinopathy, 5% with cardiac conduction abnormality, and 22.5% having endocrinopathy (most often thyroid dysfunction rather than diabetes). Neurophysiology abnormalities included length-dependent axonal polyneuropathy in 44% (sometimes subclinical) and myopathic EMG changes in 26%. Exposure to sources of acquired mitochondrial toxicity including cigarette use and hepatitis C infection were more common than expected in this series. DISCUSSION: Phenotype was different in this late-onset series compared with previous reports in CPEO patients. In this series of late-onset patients, multi-organ dysfunction was more common than previously reported in CPEO, and some classical mitochondrial manifestations, such as pigmentary retinopathy were rare. We suggest that acquired mitochondrial toxicity may have a role in the pathogenesis of adult-onset CPEO.

[Chronic progressive external ophthalmoplegia: clinical and electromyographic manifestations in a series of cases]. / Oftalmoplejía externa progresiva crónica: manifestaciones clínicas y electromiográficas en una serie de casos.

INTRODUCTION: Chronic progressive external ophthalmoplegia (CPEO) is a common mitochondrial disease. The different conditions in this group of diseases overlap clinically, enzymatically and genetically. There is no effective treatment. Ptosis improves with corrective surgery involving tarsorrhaphy as a palliative measure. CASE REPORTS: Code numbers were examined in a retrospective study conducted in order to search for patients with ptosis or ophthalmoplegia who had either visited or been admitted to the neurology department over the last 10 years. Data concerning these patients' clinical features and results of complementary tests were collected. Six patients with CPEO were identified, five of whom were females. Ages ranged from 44 to 72 years. All the patients had ptosis, although 50% were asymmetric. Half of them reported mild dysphagia while swallowing liquids. Levels of creatine phosphokinase and acetylcholine antireceptor antibodies were normal. Half the patients showed increased jitter and a muscle biopsy revealed that five of them had ragged red fibres. The most frequent enzyme deficit was complex I and IV deficiency. There were no familial forms; the most common genetic anomaly was single deletion in the mitochondrial deoxyribonucleic acid. CONCLUSIONS: In cases of ptosis and ophthalmoplegia that do not respond to anticholinesterases, knowledge of this condition makes it possible to avoid the use of immunosuppressant drugs, which have important side effects.

Oftalmoplejía externa progresiva crónica: manifestaciones clínicas y electromiográficas en una serie de casos / Chronic progressive external ophthalmoplegia: clinical and electromyographic manifestations in a series of cases

Introducción. La oftalmoplejía externa progresiva crónica(CPEO) es una enfermedad mitocondrial común. Este grupode enfermedades presenta solapamiento clínico, enzimático y genéticoentre las diferentes entidades. No existe un tratamiento eficaz.La ptosis mejora con cirugía correctora de tarsorrafia comouna medida paliativa. Casos clínicos. Estudio retrospectivo en elque se busca por codificación a pacientes con ptosis u oftalmoplejíaen consultas o ingresados en neurología durante los últimos 10años. Se recogieron datos de la clínica y pruebas complementariasde estos pacientes. Se identificó a seis pacientes con CPEO; cincode ellos fueron mujeres. Sus edades estaban comprendidas entrelos 44 y los 72 años. Todos los pacientes presentaban ptosis, aunqueel 50% era asimétrica. La mitad refería disfagia leve paralíquidos. Los niveles de creatinfosfocinasa y de anticuerpos antirreceptoresde acetilcolina fueron normales. Existía un aumentodel jitter en la mitad de los pacientes y fibras rojas rasgadas en labiopsia muscular de cinco de ellos. El déficit enzimático más frecuentefue el de los complejos I y IV. No existieron formas familiares;la anomalía genética más común fue la deleción única en elácido desoxirribonucleico mitocondrial. Conclusión. El conocimientode esta entidad permite, en casos de ptosis y oftalmoplejíaque no responden a anticolinesterásicos, evitar el uso de medicacionesinmunosupresoras con efectos secundarios importantes

Introduction. Chronic progressive external ophthalmoplegia (CPEO) is a common mitochondrial disease. Thedifferent conditions in this group of diseases overlap clinically, enzymatically and genetically. There is no effective treatment.Ptosis improves with corrective surgery involving tarsorrhaphy as a palliative measure. Case reports. Code numbers wereexamined in a retrospective study conducted in order to search for patients with ptosis or ophthalmoplegia who had eithervisited or been admitted to the neurology department over the last 10 years. Data concerning these patients' clinical featuresand results of complementary tests were collected. Six patients with CPEO were identified, five of whom were females. Agesranged from 44 to 72 years. All the patients had ptosis, although 50% were asymmetric. Half of them reported mild dysphagiawhile swallowing liquids. Levels of creatine phosphokinase and acetylcholine antireceptor antibodies were normal. Half thepatients showed increased jitter and a muscle biopsy revealed that five of them had ragged red fibres. The most frequentenzyme deficit was complex I and IV deficiency. There were no familial forms; the most common genetic anomaly was singledeletion in the mitochondrial deoxyribonucleic acid. Conclusions. In cases of ptosis and ophthalmoplegia that do not respondto anticholinesterases, knowledge of this condition makes it possible to avoid the use of immunosuppressant drugs, which haveimportant side effects

Frequency of dystrophic muscle abnormalities in chronic progressive external ophthalmoplegia: analysis of 86 patients.

BACKGROUND: There are few reports describing the coexistence of dystrophic features with those typical of mitochondrial myopathies in muscle biopsy. A recent study suggested that dystrophic features are frequent in patients with chronic progressive external ophthalmoplegia (CPEO) with a high mutation load, but the actual frequency of these abnormalities in CPEO remains undetermined. OBJECTIVE: To review the occurrence of dystrophic abnormalities in a large series of patients with CPEO to assess the frequency of such abnormalities and to verify whether they are correlated with specific mitochondrial DNA (mtDNA) mutations. METHODS: Retrospective survey of case series (86 patients with CPEO). RESULTS: Only three cases with dystrophic abnormalities were found: two with a large scale mtDNA deletion and one with the A3251G mutation. All three patients showed predominantly proximal muscular weakness resembling limb girdle muscular dystrophy. CONCLUSIONS: Dystrophic abnormalities are rare in CPEO and are not correlated with a specific molecular defect.

Prevalence of large-scale mitochondrial DNA deletions in an adult Finnish population.

BACKGROUND: Large-scale mitochondrial DNA (mtDNA) deletions are associated with clinical conditions such as Kearns-Sayre syndrome and chronic progressive external ophthalmoplegia in adults and Pearson syndrome in children. Reported case series have suggested that deletions are not uncommon in the population, but their prevalence has not been documented. METHODS: The authors ascertained patients with clinical features associated with mtDNA deletions in a defined adult population in northern Finland. Buccal epithelial samples were requested from each patient fulfilling the selection criteria, and full-length mtDNA was amplified using the long PCR method. Deletion breakpoints were identified using sequencing. Patients with deletions were examined clinically. RESULTS: The authors identified four patients with single large-scale mtDNA deletions. The prevalence of deletions was calculated to be 1.6/100,000 in the adult population in the province of Northern Ostrobothnia (0.0 to 3.2; 95% CI). Analysis of incident cases from a neighboring province revealed two patients with deletions and yielded a similar population frequency. CONCLUSIONS: The frequency of large-scale mitochondrial DNA deletions is similar among populations, suggesting that there is a constant rate of new deletions.

Deleción en el ADN mitocondrial de una paciente brasileña con oftalmoplejía crónica progresiva externa / A single deletion of mitocondrial DNA in a Brazilian patient with chronic progressive external ophthalmoplegia

Introducción. El síndrome de oftalmoplejía crónica progresiva externa (CPEO) se ha asociado a la presencia de grandes deleciones, únicas o múltiples, en el ADN mitocondrial (ADNmt) del tejido muscular esquelético. Caso clínico. Presentamos un caso esporádico de CPEO que comenzó a los 19 años de edad y que se asocia a la presencia de fibras rojas rasgadas en el músculo esquelético. El análisis genético del ADNmt mostró la presencia de una deleción única de 4.237 pb, comprendida entre los nucleótidos 9486 y 13722, y flanqueada por una repetición directa. Conclusiones. La cantidad de moléc ulas de ADNmt delecionadas en el músculo de esta paciente (55%) sugiere que esta deleción es la causa molecular de la presentación fenotípica de esta paciente (AU)

Introduction. The syndrome of chronic progressive external ophthalmoplegia (CPEO) has been associated to the presence of large deletion, single or multiple, in the mitochondrial DNA of skeletal muscle. Case report. We report a sporadic case of chronic progressive external ophthalmoplegia that began at age 19 years and was associated with ragged-red fibers in skeletal muscle. Genetic analysis of mitochondrial DNA revealed the presence of a single deletion of 4237 bp that encompasses the nucleotide positions 9486 to 13722, a location that has not been described before, and flanked by a direct repeat sequence. The deletion is flanked by a direct repeat. Conclusions. The amount of deleted mitochondrial DNA (55%) in this patient’s muscle suggests that this deletion is the molecular cause of the phenotypic presentation of this patient(AU)

Prevalence and progression of mitochondrial diseases: a study of 50 patients.

We report 50 patients with various clinical phenotypes of mitochondrial disease studied over the past 10 years in a large urban area (Madrid Health Area 5). The clinical phenotypes showed a large variety of abnormalities in molecular biology and biochemistry. The prevalence of mitochondrial diseases was found to be 5.7 per 100,000 in the population over 14 years of age. Clinical and electrophysiological assessment reveal signs of neuropathy in 10 patients. Electromyographic findings consistent with myopathy were obtained in 37 cases. Six patients died of medical complications. Disease phenotype influenced survival to some degree (P < 0.01). Age of onset and gender were not associated with differences in survival. Mitochondrial disease is thus far more common than expected and a common cause of chronic morbidity.

Mutations of ANT1, Twinkle, and POLG1 in sporadic progressive external ophthalmoplegia (PEO).

To verify the impact of mutations in ANT1, Twinkle, and POLG1 genes in sporadic progressive external ophthalmoplegia associated with multiple mitochondrial DNA (mtDNA) deletions, DNA samples from 15 Italian and 12 British patients were screened. Mutations in ANT1 were found in one patient, in Twinkle in two patients, and in POLG1 in seven patients. Irrespective of the inheritance mode, screening of these genes should be performed in all patients with progressive external ophthalmoplegia with multiple mtDNA deletions.

Mutation of POLG is associated with progressive external ophthalmoplegia characterized by mtDNA deletions.

Progressive external ophthalmoplegias (PEO) characterized by accumulation of large-scale mitochondrial DNA (mtDNA) deletions are rare human diseases. We mapped a new locus for dominant PEO at 15q22-q26 in a Belgian pedigree and identified a heterozygous mutation (Y955C) in the polymerase motif B of the mtDNA polymerase gamma (POLG). We identified three additional POLG missense mutations compatible with recessive PEO In two nuclear families. POLG is the only DNA polymerase responsible for mtDNA replication.

Human mitochondrial DNA deletions associated with mutations in the gene encoding Twinkle, a phage T7 gene 4-like protein localized in mitochondria.

The gene products involved in mammalian mitochondrial DNA (mtDNA) maintenance and organization remain largely unknown. We report here a novel mitochondrial protein, Twinkle, with structural similarity to phage T7 gene 4 primase/helicase and other hexameric ring helicases. Twinkle colocalizes with mtDNA in mitochondrial nucleoids. Screening of the gene encoding Twinkle in individuals with autosomal dominant progressive external ophthalmoplegia (adPEO), associated with multiple mtDNA deletions, identified 11 different coding-region mutations co-segregating with the disorder in 12 adPEO pedigrees of various ethnic origins. The mutations cluster in a region of the protein proposed to be involved in subunit interactions. The function of Twinkle is inferred to be critical for lifetime maintenance of human mtDNA integrity.

[Molecular studies in Cuban patients with progressive external ophthalmoplegia]. / Estudios moleculares en pacientes cubanos con oftalmoplejía externa progresiva.

INTRODUCTION: The mitochondria, subcellular organelles which possess their own DNA (mtDNA), produce most of the energy, in the form of ATP, which is necessary for life. This mtDNA may have diverse molecular defects which have been associated with a great variety of clinical syndromes. Deletions in mtDNA are one of the common mutations in patients with mitochondrial myopathies, which in the great majority present with the common symptom of progressive external ophthalmoplegia. In this study we report our findings in eight Cuban families with suspected mitochondrial disease. OBJECTIVES: To characterize these patients from the molecular point of view, which would allow a preliminary understanding of the behavior of these deletions in Cuban patients. PATIENTS AND METHODS: We studied nine patients from eight Cuban families in whom mitochondrial encephalomyopathy was suspected. We analyzed the presence of ragged red fibres, the enzymatic activity of the mitochondrial respiratory chain and detection of mtDNA mutations. We used the technique of restriction length polymorphism analysis for detection of deletions. RESULTS: Histochemical studies showed the presence of COX negative ragged red fibres in seven of the patients studied. The enzymatic activity of the mitochondrial respiratory chain was normal in all the patients. We detected four patients with single deletions of mtDNA, and one with multiple deletions and of the patients had the A3243G mutation. CONCLUSIONS: With the methods used we were able to determine the presence of a mitochondrial disorder in seven of the eight families studied and deletions of mtDNA were detected as the cause of the illness in five. The disorder was always associated with progressive external ophthalmoplegia and COX negative ragged red fibres.