Mitochondrial myopathy and lactic acidaemia with myoclonic epilepsy, ataxia and hypothalamic infertility: a variant of Ramsay-Hunt syndrome?

Boucher-Neuhäuser syndrome: cerebellar degeneration, chorioretinal dystrophy and hypogonadotropic hypogonadism: two novel cases and a review of 40 cases from the literature

The combination of progressive cerebellar degeneration, hypogonadotropic hypogonadism and chorioretinal dystrophy defines the rare Boucher-Neuhäuser syndrome (BNS), which has recently been linked to autosomal-recessive mutations in the PNPLA6 gene in four index patients. Here we present two novel unrelated patients with BNS, where we identified four recessive PNPLA6 mutations (3 of them novel) as the genetic cause, using a targeted high-throughput approach. This finding provides the first replication from independent families that BNS is caused by PNPLA6 and, moreover, highlights PNPLA6 as the major gene leading to BNS. Given the fact that the major gene causing BNS has thus now been identified, we summarize the spectrum of clinical presentations and phenotype evolution of BNS based on a systematic in-depth review of the literature of previously published cases (n = 40). Both the two cases presented here and our review of the literature propose that the clinical presentation of BNS can be variable regarding both the age (ranging from 1 to 40 years) and the clinical symptoms at onset (cerebellar ataxia in 38 %; vision loss in 36 %; delayed puberty in 26 %). A substantial fraction of BNS cases may present with relatively selective atrophy of the superior and dorsal parts of the cerebellar vermis along with atrophy of the cerebellar hemispheres on MRI, while brainstem or cortical changes on MRI seem to be present only in small fractions. Also in the literature, no other major genetic causes of BNS other than PNPLA6 mutations were identified.

Other autosomal recessive and childhood ataxias

The label of "early-onset cerebellar ataxia with retained tendon reflexes" (EOCA) has been created to differentiate it from Friedreich ataxia (FRDA) patients with preserved knee jerks and absence of cardiomyopathy, optic atrophy, and diabetes mellitus. However, EOCA is a heterogeneous syndrome and several FRDA patients present with an EOCA-like phenotype. Cerebellar ataxia with hypogonadism is another heterogeneous syndrome for which no locus has been mapped yet. Two peculiar ataxic syndromes have been identified in genetically isolated populations: autosomal recessive ataxia of Charlevoix-Saguenay (ARSACS) in Quebec and infantile-onset spinocerebellar ataxia (IOSCA) in Finland. Both conditions present usually within the second year of life. ARSACS is characterized by marked spasticity and IOSCA by a complex phenotype which includes, besides ataxia, epilepsy, optic atrophy, ophthalmoplegia, hearing loss, and areflexia. The responsible genes are SACS, encoding sacsin, a protein which may act as a chaperone, and C10orf2, encoding Twinkle, a mitochondrial DNA-specific helicase. Marinesco-Sjögren syndrome, clinically characterized by cerebellar ataxia, cataracts, myopathy, and mental retardation, is genetically heterogeneous. One gene, SIL1, encodes a nucleotide exchange factor for the heat-shock protein 70 chaperone HSPA5. Five conditions account for most cases of progressive myoclonic ataxia: Unverricht-Lundborg disease, Lafora disease, myoclonic epilepsy with ragged-red fibers, neuronal ceroid lipofuscinoses, and sialidoses.

Early-onset cerebellar ataxia, myoclonus and hypogonadism in a case of mitochondrial complex III deficiency treated with vitamins K3 and C

A 16-year-old girl presented with early-onset cerebellar ataxia, myoclonus, elevated lactic acidosis and hypogonadotropic hypogonadism. Muscle biopsy specimens revealed fibres with a "ragged" appearance with increased mitochondria and lipid droplets. Biochemical investigation revealed a deficiency of complex bc1 (complex III) of the mitochondrial respiratory chain. Genetic analysis did not show either deletions or known mutations of mitochondrial DNA (mtDNA). Phosphorus magnetic resonance spectroscopy (31P-MRS) showed defective energy metabolism in brain and gastrocnemius muscle. A decreased phosphocreatine (PCr) content was found in the occipital lobes accompanied by normal inorganic phosphate (Pi) and cytosolic pH. These findings represented evidence of a high cytosolic adenosine diphosphate concentration and a relatively high rate of metabolism accompanied by a low phosphorylation potential. Muscle 31P-MRS showed a high Pi content at rest, abnormal exercise transfer pattern and a low rate of PCr post-exercise recovery. These findings suggested a deficit of mitochondrial function. Therapy with vitamins K3 and C normalized brain 31P-MRS indices, whereas it did not affect muscle bioenergetic metabolism. In this patient, the endocrinological disorder is putatively due to a mitochondrial cytopathy. Although an unknown mtDNA mutation cannot be ruled out, the genetic defect may lie in the nuclear genome.

Myoclonic epilepsy with ragged-red fibers (MERRF) syndrome: report of a Chinese family with mitochondrial DNA point mutation in tRNA(Lys) gene

We report myoclonic epilepsy with ragged-red fibers (MERRF) syndrome in a Chinese family with confirmed mitochondrial DNA point mutation. Six members of the family including the grandmother, two siblings, and three grandchildren were affected. Among them, action myoclonus was seen in five; short stature, muscle weakness, and mental retardation in four; lactic acidosis, hearing impairment, and ataxia in two; and seizures in one. Muscle biopsy from two affected siblings revealed ragged-red fibers and abundant subsarcolemmal mitochondria with paracrystalline inclusions. Pedigree analysis suggests a maternal transmission. Analysis of mitochondrial DNA showed a point mutation from A to G at the 8344th nucleotide position located in the tRNA(Lys) gene. To our knowledge, this is the first report of MERRF syndrome with such genetic defect from a Chinese family. The present and previous reports support the notion that mitochondrial DNA point mutation at the 8344th nucleotide position is the most common cause of MERRF syndrome.

Association of progressive myoclonic epilepsy and spinal muscular atrophy

It is well known that certain hereditary diseases of the nervous system sometimes occur concurrently within particular families. This report presents a Yugoslav family of Hungarian origin in whom 2 brothers had progressive myoclonic epilepsy and proximal weakness and atrophy of muscles. Electromyography and muscle biopsy confirmed neurogenic atrophy. Electroencephalography disclosed paroxysmal spike-and-wave and polyspike-and-wave complexes with photic-induced myoclonic jerking. The combination of these clinical features is extremely rare and probably constitutes a clinical syndrome that has not been reported previously.

Heterogeneous findings in four cases of cerebellar ataxia associated with hypogonadism (Holmes' type ataxia)

We report four sporadic cases of cerebellar ataxia associated with hypogonadism. All patients were female. The neurological symptoms appeared in the first three decades. Apart from ataxia, the most frequent features were nystagmus, dysarthria, mental impairment, brisk tendon reflexes, skeletal deformities, peripheral neuropathy, and tremor. Neuroimaging studies showed constant cerebellar atrophy, in some instances associated with involvement of either grey or white cerebral matter. Neurophysiological studies demonstrated an axonal neuropathy. Endocrine evaluation showed heterogeneity of the hypogonadism, which was hypogonadotrophic in one patient and hypergonadotrophic in the other three. One patient had partial deficiency of muscle cytochrome c oxidase. The syndrome appears to be a heterogeneous multisystem disorder and in some cases a mitochondrial metabolism deficiency could be suspected.

Muscle histopathology in myoclonus epilepsy with ragged-red fibers (MERRF)

Histopathologic findings were examined in skeletal muscle biopsies from 6 patients with myoclonus epilepsy with ragged-red fibers (MERRF) who had an A to G base substitution at mitochondrial DNA (mtDNA) nucleotide pair 8344. In addition to variation in fiber size and ragged-red fibers, all specimens in cross sections showed focal cytochrome c oxidase (CCO) deficiency, suggesting that this finding is crucial in elucidating the role of the mutant mtDNA in the pathogenesis of this disorder. Along the length of single muscle fibers, defects in CCO activity were distributed segmentally with blurred borders in 5 patients which were in contrast with segmental defects with sharply delineated borders seen in chronic progressive external ophthalmoplegia with deleted mtDNA. These morphologically heterogeneous defects in CCO activity may in part be due to differing populations of and distributions of wild and mutants mtDNAs.

Ramsay Hunt syndrome with mental disorder

This is a case of Ramsay Hunt syndrome with mental disorder. The patient had action myoclonus, grand mal seizure and severe cerebellar ataxia. Schizophrenia-like symptoms including delusion of persecution and self-reference, auditory hallucination and incoherence were characteristically observed before the neurological disturbance became manifest. Subsequently, euphoria, disinhibition, moria and mild dementia appeared with neurological symptoms. The possibility of Ramsay Hunt syndrome to accompany organic mental syndromes and the relationship between cerebellar dysfunction and psychiatric symptoms are discussed.

Multiple defects of the mitochondrial respiratory chain in a mitochondrial encephalopathy (MERRF): a clinical, biochemical and molecular study

We describe a young man with a progressive neurological disorder including myoclonus, mental retardation, muscle weakness and a mitochondrial myopathy (myoclonus epilepsy and ragged red fibres--MERRF). Multiple abnormalities of the mitochondrial respiratory chain in skeletal muscle are shown by direct measurement of the flux through the individual complexes, low-temperature redox spectroscopy and decreased immunodetectable subunits of complexes I and IV by immunoblotting. No abnormality of mitochondrial DNA was found. This is the first report of combined defects of complexes I, III and IV as a cause of this clinical syndrome. However, we propose that the occurrence of multiple respiratory chain defects may be more common than previously recognised and that this particular combination of defects, involving complexes I, III and IV, may be the predominant biochemical abnormality in MERRF.

Mitochondrial myopathy and myoclonic epilepsy

The authors describe a family (mother, son and two daughters) with mitochondrial myopathy. The mother was asymptomatic. Two daughters had lactic acidosis and myoclonic epilepsy, mild dementia, ataxia, weakness and sensory neuropathy. The son suffered one acute hemiplegic episode due to an ischemic infarct in the right temporal region. All the patients studied had hypertension. EEG disclosed photomyoclonic response in the proband patient. Muscle biopsy disclosed ragged-red fibers and abnormal mitochondria by electron microscopy. Biochemical analysis showed a defect of cytochrome C oxidase in mitochondria isolated from skeletal muscle. Several clinical and genetic aspects of the mitochondrial encephalomyopathies are discussed.

Improvement of action myoclonus by an administration of 5-hydroxytryptophan and carbidopa in a child with muscular subsarcolemmal hyperactivity

We report a 3-year-11-month-old boy who manifested action myoclonus only. Histochemical analysis of the quadriceps muscle revealed subsarcolemmal hyperactivity. The administration of 5-hydroxytryptophan and carbidopa dramatically improved the action myoclonus and reduced an amplitude of giant somatosensory evoked potentials. A nosological relation of this case with "essential myoclonus" and mitochondrial encephalomyopathy was discussed.

Mitochondrial encephalomyopathy with corticosteroid dependence

A 12-year-old boy with corticosteroid-responsive mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) is described. His mother proved to have an asymptomatic mitochondrial myopathy on examination of a muscle biopsy specimen. Three weeks after the onset of vomiting, headache, ataxia and visual and speech impairment, he presented with a background of somatic growth retardation, deafness and school failure. Examination revealed disorientation, dysphasia, dyspraxia, optic atrophy, hemianopia, hemiparesis and sensory inattention. A cranial computed tomographic scan disclosed a large, low-density area, which was consistent with infarction, in the left posterior hemisphere and marked calcification of the basal ganglia bilaterally. Within two weeks of the commencement of corticosteroid treatment, the neurological dysfunction resolved. Attempts to decrease the dosage of dexamethasone caused an exacerbation of symptoms repeatedly. Two weeks after ceasing corticosteroid therapy, the patient developed a serious neurological relapse and a new, large, low-density area, which resembled an infarction, in the right posterior hemisphere on a computed tomographic scan. The reintroduction of corticosteroid therapy again resulted in the rapid resolution of all symptoms. It became evident that the patient had an exquisitely sensitive corticosteroid dependency, whereby a reduction in the dexamethasone dosage of even 0.25 mg a day caused confusion, headaches and increasing lactic acidaemia. Although it is difficult to assess the impact of various therapies in MELAS because of the episodic natural course of the disease, this remarkable corticosteroid responsiveness also has been noted in four previously reported patients with MELAS syndrome; therefore, it would seem reasonable to suggest that corticosteroid therapy now should be considered as standard treatment for this condition. However, corticosteroid therapy in other forms of mitochondrial disorders still awaits careful evaluation.

Myoclonic epilepsy and ragged-red fibers with cytochrome oxidase deficiency: neuropathology, biochemistry, and molecular genetics

A 36-year-old man with myoclonic epilepsy and ragged-red fibers (MERRF) died after more than 18 years of follow-up study. He was 1 of 3 affected siblings and the offspring of an affected mother, suggesting maternal transmission. At autopsy, there was neuronal loss and gliosis in the dentate nucleus of the cerebellum and in the inferior olivary nucleus. Skeletal muscle showed ragged-red fibers, and paracrystalline inclusions in mitochondria by electron microscopy. Biochemical analysis showed a generalized partial defect of cytochrome c oxidase (COX) in mitochondria isolated from all tissues, including brain, heart, skeletal muscle, kidney, and liver. The Michaelis constant (Km) for cytochrome c was abnormally low, suggesting a defect of the mitochondrially encoded subunit II of COX. Immunological studies (enzyme-linked immunosorbent assay, dot-blot, Western blot, and immunohistochemistry) showed that the holoenzyme was decreased but subunit II was decreased more than the holocomplex or the nuclearly encoded subunit IV. However, Northern and Southern blots showed that the gene for subunit II, as well as the genes for subunits I, III, IV, and VIII, were of normal size and were normally transcribed. A point mutation or a small deletion of mitochondrial DNA, probably affecting the COX-II gene, may be responsible for the COX deficiency in this case of MERRF.

Dyssynergia cerebellaris myoclonica (Ramsay Hunt syndrome): a condition unrelated to mitochondrial encephalomyopathies

Thirteen patients with dyssynergia cerebellaris myoclonica (Ramsay Hunt syndrome) had full clinical and neurophysiological study as well as muscle biopsy. The patients had action myoclonus, generalised epileptic seizures, and mild cerebellar syndrome. The disease was inherited in an autosomal recessive pattern in five patients, and occurred as isolated cases in the remaining eight patients. The age at onset of symptoms ranged from 6 to 15 years (mean, 10.4 years). The EEG and polygraphic findings included normal background activity in most patients, spontaneous fast generalised spike-and-wave discharges, photosensitivity, no activation during slow sleep, and vertex and rolandic spikes in REM sleep. Results of muscle biopsy, performed an average of 14 years after onset of the disease, were normal and showed no mitochondrial abnormalities. These findings suggest that Ramsay Hunt syndrome is a condition with distinctive clinical and neurophysiological features and unrelated to mitochondrial encephalomyopathies.

Normal muscle mitochondrial function in Ramsay-Hunt syndrome

Mitochondrial encephalomyopathies may display clinical features similar to Ramsay-Hunt syndrome (RHS). We studied muscles mitochondrial function in 2 patients with RHS. Histochemical and ultrastructural studies of muscle biopsies and biochemical analysis of muscle mitochondrial enzymes were normal. There is no evidence for a disturbance of muscle mitochondrial function in RHS.

Endocrine involvement in mitochondrial encephalomyopathy with partial cytochrome c oxidase deficiency

A 19-year-old man born with thyroprivic hypothyroidism, due to congenital development defect, manifested hypogonadism, stunted growth, chronic progressive external ophthalmoplegia (CPEO), diffuse muscle weakness and wasting, right bundle branch block, cerebral atrophy. Muscle biopsy showed mitochondrial abnormalities. Biochemical investigations on muscle disclosed partial (50%) cytochrome c oxidase deficiency, 58% decrease of cytochrome aa3 and 41% decrease of cytochrome b. Enzyme-linked immunosorbent assay showed decrease of the immunologically active enzyme protein.

Familial mitochondrial encephalomyopathy (MERRF): genetic, pathophysiological, and biochemical characterization of a mitochondrial DNA disease

A large MERRF pedigree permitted the direct testing of the predictions for a mitochondrial DNA (mtDNA) mutation. A mtDNA mutation was demonstrated by proving maternal inheritance and by identifying specific deficiencies in muscle energetics and mitochondrial respiratory complexes I and IV. mtDNA heteroplasmy (a mixture of mutant and wild-type mtDNAs) was demonstrated by showing variation in the mitochondrial energetic capacity between family members. The phenotypic consequences of differential tissue-specific reliance on mitochondrial ATP was shown by correlating individual respiratory deficiency with the nature and severity of patients' clinical manifestations. The observed spectrum of clinical manifestations resulting from this heteroplasmic mtDNA mutation implies that mtDNA disease may be much more prevalent than previously anticipated.

Mitochondrial myopathies with necrotizing encephalopathy of the Leigh type

Two patients with mitochondrial encephalomyopathy (MEP) serve to emphasize the variability of this group of diseases. Cerebral insults, mitochondrial cardiopathy, relapsing ileus, cerebral angioma, ataxia, and myoclonic seizures characterized the first case of an adult man with similar diseases in his family, interpreted as transitional form between mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) and myoclonus epilepsy associated with ragged red fibers (MERRF). The second patient, a floppy infant with cardiomyopathy and myoclonism, statomotoric and mental retardation showed combined defects in mitochondrial respiratory chain at NADH-CoQ reductase and cytochrome c oxidase and a deficiency of carnitine. In both patients neuropathologically criteria of Leigh's syndrome could be demonstrated in the cerebral cortex, in case 2 also clinically. The classificatory problems of the relationships between KSS, MELAS, MERRF, Leigh's as well as Alpers' syndromes are discussed.

Mitochondrial myopathy: a genetic study of 71 cases

Of 71 index cases with histologically defined mitochondrial myopathy, 13 (18%) had relatives who were definitely affected with a similar disorder. Eight familial cases from four families were confined to a single generation. In five families maternal transmission to offspring occurred. There were no instances of paternal transmission, but one patient had an affected cousin in the paternal line. No consistent clinical syndrome or pattern of inheritance emerged for any identified defect of the mitochondrial respiratory chain, localised biochemically in 41 cases. Overall, the recurrence rate was 3% for sibs and 5.5% for offspring of index cases. Review of published reports of familial cases of mitochondrial myopathy suggests that the ratio of maternal to paternal transmission is about 9:1. We conclude that these disorders may be caused by mutations of either nuclear or mitochondrial genes.

Mitochondrial encephalo-neuro-myopathy with myoclonus epilepsy, basal nuclei calcification and hyperlactacidemia

We report a new case of MERRF (myoclonus epilepsy with ragged red fibers) syndrome with basal nuclei calcification on the brain CT scan, without hormonal abnormalities, with high CSF protein and hyperlactacidemia, juvenile onset and death at 18 years. Biochemical study of mitochondrial muscle enzymes showed decreased NADH-cytochrome-C-reductase and Succinate-cytochrome C-reductase activity, suggesting a Complex III defect of the respiratory chain. Similar reported cases are reviewed.

Biochemical studies in mitochondrial encephalomyopathy

The alpha-keto acid dehydrogenase complex and its component enzymes, lactate dehydrogenase, pyruvate carboxylase, cytochrome c oxidase, succinate-cytochrome c reductase, NADH-cytochrome c reductase, and the concentration of cytochromes and enzymes of beta-oxidation in muscle from a patient with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes were studied and no specific defect was found. These results raise the possibility that the mitochondrial changes in the patient may be secondary.

Transient postictal cortical blindness

An 8-year-old boy with insulin-dependent diabetes mellitus and a seizure disorder demonstrated transient visual loss after severe seizure activity. The role of hypoglycemia in relation to his transient cortical blindness remains indeterminate. The nature of the cortical involvement, the rate of visual recovery, and prior reports of postictal phenomena emphasize the relatively benign nature of this condition in children.

Computed tomography and angiography in MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes); report of 3 cases

Among mitochondrial encephalomyopathies, MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes, Pavlakis et al. 1983) is recognized as a distinct syndrome characterized by generalized convulsions and recurrent stroke-like episodes. The neuroradiological findings of three patients with MELAS are reported here. Retrospective review shows that MELAS should be included in the differential diagnosis of infarct-like lesions of the cerebrum.

Peripheral neuropathy associated with mitochondrial myopathy

Twenty patients with mitochondrial myopathy were investigated for the presence of peripheral neuropathy. There were clinical features of a mild sensorimotor neuropathy in 5 patients (25%) and nerve conduction studies were abnormal in 10 patients (50%). Electrophysiological studies of the whole group showed significant impairment of motor and sensory conduction, compared with controls. Sural nerve biopsy and morphometric studies were performed on 4 patients with clinical neuropathy. There was a reduction in density of myelinated fibers and electron microscope features of axonal degeneration affecting myelinated and unmyelinated fibers. Abnormal mitochondria containing paracrystalline inclusions were seen in the Schwann cell cytoplasm of two nerves.

Ramsay Hunt syndrome and coeliac disease: a new association?

Two patients with the syndrome of Ramsay Hunt (dyssynergia cerebellaris myoclonica, DCM), associated with malabsorption due to adult coeliac disease, are reported. Both presented with progressive cerebellar ataxia, action myoclonus, and epilepsy. One had gastrointestinal symptoms (recurrent diarrhea and weight loss which responded satisfactorily to a gluten-free diet), but the other did not. In both patients, jejunal biopsy revealed subtotal villous atrophy; serum folate and vitamin E level were also reduced. Neither a gluten-free diet nor vitamin supplements improved the neurological picture. However, some symptomatic relief was afforded by treatment with clonazepam, sodium valproate, carbamazepine, and piracetam. It could be argued that the association between these two disorders is coincidental. However, since we have found this combination in 2 of 14 consecutive cases with DCM, a causal relationship seems likely, although the underlying mechanism remains unknown. Patients with the Ramsay Hunt syndrome should be investigated for malabsorption, and also undergo small intestinal biopsy.

Mitochondrial myoneuropathy with respiratory failure and myoclonic epilepsy. A case report with biochemical studies

A 55-year-old man is presented who developed severe multifocal myoclonus and tonic clonic seizures in his early thirties, and progressive limb weakness in his mid forties, when a ragged red fibre myopathy was diagnosed. He went on to develop a distal motor neuropathy and respiratory failure. Respiratory function tests indicated respiratory failure secondary to respiratory muscle weakness and a central hypoventilation syndrome. CT scan revealed brain stem atrophy and brain stem evoked responses were abnormal. A sural nerve biopsy showed severe axonal degeneration. Cytochrome difference spectra and polarographic studies on isolated intact muscle mitochondria were normal. This study reports the association of respiratory failure and sleep apnoea with Fukuhara's syndrome and presents biochemical data suggesting that the mitochondrial respiratory chain may be intact in some patients with this syndrome.

A mitochondrial encephalomyopathy. A combined 31P magnetic resonance and biochemical investigation

A 15-year-old girl presented with recurrent encephalopathic episodes, epilepsy, myopathy and chronic lactic acidosis. A muscle biopsy revealed the presence of ragged red fibres and mitochondria with paracrystalline inclusions. Biochemical studies on freshly isolated skeletal muscle mitochondria demonstrated a deficiency of NADH-CoQ reductase activity. Investigation of her gastrocnemius muscle at rest by phosphorus nuclear magnetic resonance displayed a reduced phosphocreatine concentration with elevated levels of inorganic phosphate and ADP. Abnormalities were also apparent in her brain spectrum. It is therefore possible that the mitochondrial defect present in skeletal muscle is also being expressed in the brain.

Maternally inherited mitochondrial myopathy and myoclonic epilepsy

A family is described with familial myoclonic epilepsy associated with mitochondrial myopathy. The disorder follows a maternal inheritance pattern consistent with a mitochondrial DNA (mtDNA) mutation. The large kindred permitted exclusion of autosomal dominant, recessive, and X-linked patterns of transmission. Several characteristics of the inheritance and variability of expression within the pedigree are consistent with recently acquired knowledge about the genetics of human mtDNA. The clinical spectrum of disease is compatible with a proportionality model of mutant and wild-type mtDNAs. Muscle biopsies of affected patients showed an increased number of abnormal muscle mitochondria. Serum levels of pyruvate or pyruvate and lactate were elevated. The most severely affected patient had constant myoclonic jerking, dementia, ataxia, spasticity, hearing loss, and hypoventilation. Cerebral dysfunction in patients with mild involvement was marked by prominent photic driving seen on electroencephalograms and high-amplitude visual and somatosensory evoked responses but no myoclonus, ataxia, or dementia. The individual clinical features of the disease worsen over time for all patients; however, mildly affected patients have not become moderately affected and moderately affected patients have not become severely affected.

Mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes: a distinctive clinical syndrome

We report on two patients who have a mitochondrial myopathy, encephalopathy, lactic acidosis, and recurrent cerebral insults that resemble strokes (MELAS). These two and nine other reported patients share the following features: ragged red fibers evident on muscle biopsy, normal early development, short stature, seizures, and hemiparesis, hemianopia, or cortical blindness. Lactic acidemia is a common finding. We believe that MELAS represents a distinctive syndrome and that it can be differentiated from two other clinical disorders that also are associated with mitochondrial myopathy and cerebral disease: Kearns-Sayre syndrome and the myoclonus epilepsy ragged red fiber syndrome. Existing information suggests that MELAS is transmitted by maternal inheritance. The ragged red fibers suggest an abnormality of the electron transport system, but the precise biochemical disorders in these three clinical syndromes remain to be elucidated.

Mitochondrial inheritance in a mitochondrially mediated disease

Mendelian inheritance involves the transmission to successive generations of DNA contained in genes in the nucleus, but DNA is also contained in mitochondria, where it is believed to be responsible for the encoding of certain mitochondrial enzymes. Since nearly all mitochondrial DNA is maternally transmitted, one might expect a nonmendelian pattern of inheritance in mitochondrial cytopathy, a syndrome in which there are abnormalities in mitochondrial structure and deficiencies in a variety of mitochondrial enzymes. We studied the pedigrees of 6 affected families whose members we had examined personally and of 24 families described in the literature. In 27 families, exclusively maternal transmission occurred; in 3 there was also paternal transmission in one generation. Altogether, 51 mothers but only 3 fathers had transmitted the condition. These results are consistent with mitochondrial transmission of mitochondrial cytopathy; the inheritance and enzyme defects of mitochondrial cytopathy can be considered in the light of recent evidence that subunits of respiratory-enzyme complexes are encoded solely by mitochondrial DNA. The occasional paternal transmission may be explained if certain enzyme subunits that are encoded by nuclear DNA are affected.

"Mitochondrial myopathy" or mitochondrial disease? EEG, ERG, VEP studies in 13 children

Neurophysiological investigations (EEG, ERG, VEP) were carried out in 13 patients with proven "mitochondrial myopathy". There were nine girls and four boys. Varied abnormalities were seen in the EEGs of all cases, and in one patient unusual repetitive bursts of irregular slow waves and spikes were observed. The ERG was abnormal in five of the 12 cases tested, while the VEP (flash) was definitely abnormal in six out of these 12 cases. These neurophysiological findings suggest some involvement of both the brain and the visual system. It seem therefore appropriate that this condition be considered a "mitochondrial disease" affecting many systems rather than only muscles.