Deletion of mitochondrial DNA in a case of early-onset diabetes mellitus, optic atrophy, and deafness (Wolfram syndrome, MIM 222300).

The Wolfram syndrome (MIM 222300) is a disease of unknown origin consisting of diabetes insipidus, diabetes mellitus, optic atrophy, and deafness. Here we report on a generalized deficiency of the mitochondrial respiratory enzyme activities in skeletal muscle and lymphocyte homogenate of a girl suffering from the Wolfram syndrome. In addition, we provide evidence for a 7.6-kilobase pair heteroplasmic deletion (spanning nucleotides 6465-14135) of the mitochondrial DNA in the two tissues and show that directly repeated sequences (11 bp) were present in the wild-type mitochondrial genome at the boundaries of the deletion. Neither of the patient's parents was found to bear rearranged molecules. This study supports the view that a respiratory chain defect can present with insulin-dependent diabetes mellitus as the onset symptom. It also suggests that a defect of oxidative phosphorylation should be considered when investigating other cases of Wolfram syndrome, especially because this syndrome fulfills the criteria for a genetic defect of the mitochondrial energy supply: (a) an unexplained association of symptoms (b) with early onset and rapidly progressive course, (c) involving seemingly unrelated organs and tissues.

Pearson's marrow-pancreas syndrome. A multisystem mitochondrial disorder in infancy.

Pearson's marrow-pancreas syndrome (McKusick No. 26056) is a fatal disorder of hitherto unknown etiology involving the hematopoietic system, exocrine pancreas, liver, and kidneys. The observation of high lactate/pyruvate molar ratios in plasma and abnormal oxidative phosphorylation in lymphocytes led us to postulate that Pearson's syndrome belongs to the group of mitochondrial cytopathies. Since rearrangements of the mitochondrial genome between direct DNA repeats were consistently found in all tissues tested, our results show that this disease is in fact a multisystem mitochondrial disorder, as suggested by the clinical course of the patients. Based on these observations, we would suggest giving consideration to the hypothesis of a defect of oxidative phosphorylation in elucidating the origin of other syndromes, especially those associated with an abnormal oxidoreduction status in plasma.

Role of cholesterol in embryonic development.

We showed previously that 3 distal inhibitors of cholesterol synthesis are highly teratogenic in rats. AY 9944 and BM 15766 inhibit 7-dehydrocholesterol reductase, which catalyzes the last step of cholesterol synthesis, and triparanol inhibits Delta(24)-dehydrocholesterol reductase, which catalyzes the last step in another pathway. These molecules cause holoprosencephalic brain anomalies. Under certain experimental conditions, other anomalies (of the limbs and male genitalia) are also observed. Assays performed by gas chromatography-mass spectrometry (GC-MS) show hypocholesterolemia and an accumulation of precursors. These data indicate that this animal model can be considered a model of Smith-Lemli-Opitz syndrome. Smith-Lemli-Opitz syndrome is a recessive autosomal genetic disease characterized by malformations (microcephaly, corpus callosum agenesis, holoprosencephaly, and mental retardation), male pseudohermaphroditism, finger anomalies, and failure to thrive. The syndrome has been attributed to a deficit in 7-dehydrocholesterol reductase. As assayed by GC-MS, the sterol status of these patients indicates severe hypocholesterolemia and an accumulation of precursors: 7-dehydrocholesterol, 8-dehydrocholesterol, and oxidized derivatives. The presence of 7-dehydrocholesterol in the serum of patients is pathognomonic of the disease. The developmental gene Shh (sonic hedgehog) plays a key role in brain, limb, and genital development; it was shown recently that the Shh protein has to be covalently linked to cholesterol to be active. This is the first time that a posttranslational function has been attributed to cholesterol. There is an obvious relation between Shh dysfunction and the malformations observed in our experiments and in patients with Smith-Lemli-Opitz syndrome. However, the exact relation remains to be clarified. It is clear, however, that the role of cholesterol in embryonic development must be taken into account.

Muscle mitochondrial DNA in encephalomyopathy and ragged red fibres: a Southern blot analysis and literature review.

Various mitochondrial DNA abnormalities have been described in patients with encephalomyopathies. We performed Southern blot analysis of skeletal muscle mitochondrial DNA in nine adult patients with clinical features and ragged red fibres suggesting mitochondrial dysfunction. Two patients with encephalomyopathy and two with the MERRF syndrome (myoclonus epilepsy with ragged red fibres) had the normal PvuII restriction pattern of muscle mitochondrial DNA. In contrast, mitochondrial DNA deletion was observed in two of six patients with ophthalmoplegia. One suffered from typical Kearns-Sayre syndrome and the other from isolated external ophthalmoplegia. None of these patients had affected relatives. The detection of mitochondrial DNA deletion in external ophthalmoplegia and their site and size support previously reported data.

Progressive left main coronary artery obstruction leading to myocardial infarction in a child with Williams syndrome.

UNLABELLED: We report a 3-year-old child with Williams syndrome in whom the first vascular feature of the syndrome was a myocardial infarction related to the occlusion of the left main coronary artery trunk. This coronary artery occlusion was not associated with supravalvular aortic stenosis. CONCLUSION: This report emphazises that acute vascular events related to systemic artery anomalies may reveal Williams syndrome.

Autosomal dominant deletions of the mitochondrial genome in a case of progressive encephalomyopathy.

Multiple deletions of the mitochondrial genome were found in a family in which the proband had ataxia and ketoacidotic comas. A progressive multiorgan involvement appeared in the course of the disease, and histopathological investigation demonstrated mitochondrial myopathy features with ragged red fibers. A defect of oxidative phosphorylation was found in both skeletal muscle and lymphocytes. It is surprising that various mtDNA deletions were detected both in the proband and in his healthy mother and maternal aunt but not in the rest of the maternal progeny. All the deletions were located between Cox II and cytochrome b genes, and short (4-5 bp) repeated sequences were consistently present at the boundaries of the rearrangements in different tissues. Therefore, the deletions appear not to be transmitted per se but to be inherited in a Mendelian manner, being possibly dominant. Both the Mendelian inheritance of the trait and the variety of the deletions in carriers suggest that a nuclearly encoded factor(s) might be involved in the triggering of the deletions. However, the presence of the rearrangements in healthy individuals raises the question of whether mtDNA deletions actually cause the clinical expression of the disease.

Clinical presentations and laboratory investigations in respiratory chain deficiency.

Respiratory chain deficiencies have long been regarded as neuromuscular diseases. In fact, oxidative phosphorylation, i.e., ATP synthesis by the respiratory chain not only occurs in the neuromuscular system, indeed, a number of non-neuromuscular organs and tissues are dependent upon mitochondrial energy supply. For this reason, a respiratory chain deficiency can theoretically give rise to any symptom, in any organ or tissue, at any age with any mode of inheritance, due to the twofold genetic origin of respiratory enzymes (nuclear DNA and mitochondrial DNA).

Clinical presentation of mitochondrial disorders in childhood.

Respiratory-chain deficiencies have long been regarded as neuromuscular diseases. In fact, oxidative phosphorylation, i.e. adenosine triphosphate (ATP) synthesis by the respiratory chain, does not occur only in the neuromuscular system. Indeed, a number of non-neuromuscular organs and tissues are dependent upon mitochondrial energy supply. For this reason, a respiratory chain deficiency can theoretically give rise to any symptom, in any organ or tissue, at any age and with any mode of inheritance, owing to the twofold genetic origin of respiratory enzymes (nuclear DNA and mitochondrial DNA, mtDNA). In recent years, it has become increasingly clear that genetic defects of oxidative phosphorylation account for a large variety of clinical symptoms in childhood. Among 100 patients with respiratory-chain deficiencies identified in our centre, 56% presented with a non-neuromuscular symptom and 44% were referred for a neuromuscular problem. It appears that the diagnosis of a respiratory-chain deficiency is difficult initially when only one symptom is present. In contrast, this diagnosis is easier to consider when two seemingly unrelated symptoms are observed.

[Cholesterol and development]. / Cholestérol et développement.

The teratogenic action of distal inhibitors of cholesterol synthesis has been known for some time. The induced malformations are of a particular type: they include holoprosencephalies. Recently these observations have solicited increased interest due to: 1/ the discovery in 1993 of a similar form of inhibition of cholesterol synthesis which is responsible for a human malformation syndrome, Smith-Lemli-Opitz; 2/ the demonstration of the involvement of the Sonic Hedgehog gene in normal development of prosencephalon and the description of the mode of action of the protein Shh: autoprocessing followed by "cholesterolisation".

Clinical aspects of mitochondrial disorders.

Mitochondrial disorders have long been regarded as neuromuscular diseases only. In fact, owing to the ubiquitous nature of the oxidative phosphorylation, a broad spectrum of clinical features should be expected in mitochondrial disorders. Here, we present eight puzzling observations which give support to the view that a disorder of oxidative phosphorylation can give rise to any symptom in any organ or tissue with any apparent mode of inheritance. Consequently, we suggest giving consideration to the diagnosis of a mitochondrial disorder when dealing with an unexplained association of symptoms, with an early onset and a rapidly progressive course involving seemingly unrelated organs. Determination of lactate/pyruvate and ketone body molar ratios in plasma can help to select patients at risk for this condition.

Maternally inherited duplication of the mitochondrial genome in a syndrome of proximal tubulopathy, diabetes mellitus, and cerebellar ataxia.

Two sisters in the first year of life presented with a proximal tubulopathy of unknown etiology. They subsequently developed a pluritissular disorder including diabetes mellitus, skin abnormalities, mitochondrial myopathy with ragged-red fibers, and cerebellar ataxia. Their mother had ptosis, ophthalmoplegia, and muscle weakness. Analysis of the mitochondrial respiratory chain showed a complex III deficiency in both skeletal muscle and lymphocytes of the second girl. Southern blot analysis provided evidence for a heteroplasmic partial duplication of the mtDNA (26 kb), involving one full-length and one partly deleted mitochondrial genome and with one single abnormal junction between the genes for ATPase 6 and cytochrome b. Using PCR amplification of lymphocyte DNA, we were able to detect minute amounts of duplicated molecules in the mother, which provided evidence for maternal inheritance of the partial duplication. While maternal transmission of point mutations have been reported in Leber disease, retinitis pigmentosa, and MERRF disease, this observation is, to our knowledge, the first example of a maternally inherited duplication of the mitochondrial genome in man.

Carrier detection in a partially dominant X-linked disease: ornithine transcarbamylase deficiency.

Ornithine transcarbamylase (OTC) deficiency is an X-linked disease responsible for lethal neonatal hyperammonemia in males. Partial OTC deficiency also occurs in females and can be responsible for life-threatening hyperammonemic comas in heterozygotes (15%). Increased orotic acid excretion occurs in both symptomatic and asymptomatic carriers, especially under protein loading tests. The disease is therefore partially dominant with neonatal lethality in the hemizygous male; the fraction of new mutations has previously been estimated to be low in males (point estimation = 0, upper bound of the confidence interval = 0.16) and 57% in females. Genetic counseling in this disease is difficult because it is not clear whether a negative protein loading test rules out carrier status. In an attempt to determine how reliable the test is for carrier detection, we investigated ten obligate carriers for orotic acid excretion; considering all data available, we concluded that the test is rarely negative in obligate carriers (8%). Consequently, a negative test in a mother decreases the minimum risk of being a carrier from 84% a priori to 30% if she had an affected son and from 43% a priori to 5% if she had a heterozygous daughter. Finally, the diagnosis of a new mutation in the germ cells of the maternal grandfather in one particular family could be ascertained by extensive DNA analysis.

Site-specific deletions of the mitochondrial genome in the Pearson marrow-pancreas syndrome.

The Pearson marrow-pancreas syndrome is a fatal disorder involving the hematopoietic system and the exocrine pancreas in early infancy. We have previously shown that this disease results from a widespread defect of oxidative phosphorylation. Here, we describe deletions of the mitochondrial (mt) genome between repeated 8- to 13-bp sequences as consistent features of the disease. Studying a series of nine unrelated children, including the patient originally reported by H. Pearson, we found five different types of direct repeats at the boundaries of the mtDNA deletions and we provided evidence for conservation of the 3'-repeated sequence in the deletions. In addition, we found a certain degree of homology between the nucleotide composition of the direct repeats and several structures normally involved in mtDNA replication and mtRNA processing. These results are consistent either with the recognition and cleavage of a particular DNA sequence with a factor of still unknown origin or with a homologous recombination between direct-repeat mtDNA sequences in the Pearson syndrome.

[Pearson's syndrome. Pancytopenia with exocrine pancreatic insufficiency: new mitochondrial disease in the first childhood]. / Syndrome de Pearson. Pancytopénie avec insuffisance pancréatique externe: une nouvelle maladie mitochondriale dans la première enfance.

Pearson's syndrome is a lethal disorder of a still unknown cause, responsible for pancytopenia and exocrine pancreatic dysfunction in the first months of life. Permanent hyperlactacidemia and increased mitochondrial and cytoplasmic oxidoreduction ratios were observed in 6 unrelated children presenting with this disease. This led to study the oxidative phosphorylation in lymphocytes and thus to relate Pearson's syndrome to an enzymatic disease of the respiratory chain (NADH oxidase activity deficiency). The study of the mitochondrial genome allowed identifying major changes in mitochondrial DNA in all patients and all studied tissues. Thus, Pearson's syndrome is the first mitochondriopathy with a non neuromuscular expression reported to date.

Hair and skin disorders as signs of mitochondrial disease.

OBJECTIVE: To compare and explore the skin manifestations of mitochondrial disorders in 14 children with puzzling and unexpected cutaneous presentations. STUDY DESIGN: One hundred forty children with mitochondrial disorders who had been under observation in our hospital for the last 10 years, were carefully examined by the same physicians. Skin and hair characteristics were investigated by the same dermatologist. All the children developed an early unexplained association of symptoms. Metabolic screening for abnormal oxidative-reduction in plasma and mitochondrial enzyme investigations confirmed the diagnosis of oxidative phosphorylation disorders. RESULTS: Fourteen children with mitochondrial disorders (10% of the original cohort) developed specific hair and skin abnormalities. Their cutaneous manifestations were similar, and could be classified into four categories: hair abnormalities, rashes and pigmentation disorders, hypertrichosis, and acrocyanosis. In 3 cases, skin disorders constituted the puzzling and unexpected manifestations of mitochondrial disease. Respiratory chain deficiencies in the cultured skin fibroblasts of 3 patients and heteroplasmic mitochondrial DNA rearrangement in the skin fibroblasts of 1 patient indicated that mitochondrial disorders may be expressed in the skin. CONCLUSION: Hair abnormalities and pigmented skin eruptions might belong to the broad spectrum of presenting symptoms of mitochondrial disease. The association of these dermatologic lesions with unrelated disorders should lead physicians to consider a diagnosis of mitochondriopathy as early as possible.

Fatal neonatal liver failure and mitochondrial cytopathy (oxidative phosphorylation deficiency): a light and electron microscopic study of the liver.

Mitochondrial cytopathies are multisystemic disorders of extremely variable expression due to a deficiency in oxidative phosphorylation. Cases have recently been reported in which fatal liver failure with neonatal onset was the major clinical and biochemical syndrome. In this series we reviewed the liver histology of 10 such patients who died in the first weeks of life (from 3 days to 6 mo). In six cases the diagnosis was confirmed by study of the mitochondrial respiratory chain in the muscle, liver or both; in the other four, appropriate tests were not available for diagnosis but symptoms were identical and all other diagnoses were ruled out. In all 10 cases we noted significant steatosis, mostly microvesicular; widespread hepatocytic, canalicular and bile duct cholestasis with bile thrombi and cholangiolar proliferation; and different degrees of hepatosiderosis and glycogen depletion. Fibrosis took varying forms: perisinusoidal, periportal with the formation of septa, even precirrhosis. In the two cases of infants who died, one at 5 and one 6 mo, micronodular cirrhosis was also present. Mitochondria, either densely or loosely packed, were abnormal-pleiomorphic with few or no cristae and a granular fluffy matrix. Dense, large granules were seen in two cases. The association of neonatal liver failure and hyperlactacidemia should lead to immediate examination of the respiratory chain. The expression of this mitochondrial cytopathy can be lethal, associated with severe liver damage due to the deficiency in oxidative phosphorylation.

Liver transplantation in mitochondrial respiratory chain disorders.

UNLABELLED: Mitochondrial respiratory chain disease may lead to neonatal or late onset liver failure, requiring liver transplantation. In rare cases, the disease is restricted to the liver and the patient is cured after surgery. More frequently, other organs are simultaneously involved and neuromuscular or other extra-hepatic symptoms may pre-exist, or appear in the post-transplant follow up. Pre-transplant evaluation should aim to rule out neurological disease, which may be difficult to differentiate from signs accompanying liver insufficiency. Cerebrospinal fluid lactic acid levels, compared to blood lactate, may be suggestive of central nervous system involvement. Of 11 cases with respiratory chain disorders who had liver transplantation in various centres, 4 are alive and well on follow up, and 6 died, three of them having developed neurological disease post orthotopic liver transplantation. All three patients with initial liver and gastro-intestinal disease died early after transplantation, indicating that these may be poor candidates for this procedure. CONCLUSION: Liver transplantation is feasible in hepatic respiratory chain disorders, but extra-hepatic disease should be ruled out before transplantation. Extra-hepatic manifestations may, however, appear and cause patient death despite successful transplantation.

A novel phenotypic pattern in X-linked inheritance: craniofrontonasal syndrome maps to Xp22.

Craniofrontonasal syndrome (CFNS, OMIM 304110) is a distinctive genetic disorder whose main clinical manifestations include coronal synostosis, widely spaced eyes, clefting of the nasal tip and various skeletal anomalies. CFNS originally was thought to be transmitted as an autosomal dominant trait, but recent studies suggest that it is X-linked dominant, whereby all daughters of males are affected, whereas none of their sons are affected. Here we report data confirming that CFNS is X-linked, mapping to a 13 cM interval in Xp22 with a maximum two-point lod score of 3.9 (theta = 0) at DXS8022 and a multipoint lod score of 5.08 at DXS1224. Detailed phenotypic analysis shows that females are more severely affected than males, a highly unusual characteristic for an X-linked disorder. CFNS represents the first multiple congenital anomaly syndrome with this unusual phenotypic pattern of X-linked inheritance.