A retrospective study of patients with the hereditary syndrome of congenital cataract, mitochondrial myopathy of heart and skeletal muscle and lactic acidosis

Adenine nucleotide carrier protein dysfunction in human disease

Adenine nucleotide translocase (ANT) is the prototypical member of the mitochondrial carrier protein family, primarily involved in ADP/ATP exchange across the inner mitochondrial membrane. Several carrier proteins evolutionarily related to ANT, including SLC25A24 and SLC25A25, are believed to promote the exchange of cytosolic ATP-Mg2+ with phosphate in the mitochondrial matrix. They allow a net accumulation of adenine nucleotides inside mitochondria, which is essential for mitochondrial biogenesis and cell growth. In the last two decades, mutations in the heart/muscle isoform 1 of ANT (ANT1) and the ATP-Mg2+ transporters have been found to cause a wide spectrum of human diseases by a recessive or dominant mechanism. Although loss-of-function recessive mutations cause a defect in oxidative phosphorylation and an increase in oxidative stress which drives the pathology, it is unclear how the dominant missense mutations in these proteins cause human diseases. In this review, we focus on how yeast was productively used as a model system for the understanding of these dominant diseases. We also describe the relationship between the structure and function of ANT and how this may relate to various pathologies. Particularly, mutations in Aac2, the yeast homolog of ANT, were recently found to clog the mitochondrial protein import pathway. This leads to mitochondrial precursor overaccumulation stress (mPOS), characterized by the toxic accumulation of unimported mitochondrial proteins in the cytosol. We anticipate that in coming years, yeast will continue to serve as a useful model system for the mechanistic understanding of mitochondrial protein import clogging and related pathologies in humans.

Sengers syndrome and AGK-related disorders - Minireview of phenotypic variability and clinical outcomes in molecularly confirmed cases

Sengers syndrome (OMIM# 212350) is a rare autosomal recessive mitochondrial disease caused by biallelic pathogenic variants in the AGK gene, which encodes the acylglycerol kinase enzyme. The syndrome was originally defined as a "triad" of hypertrophic cardiomyopathy, cataracts, and lactic acidosis, with or without skeletal myopathy. The clinical manifestation of Sengers Syndrome exhibits substantial heterogeneity, with mild and severe/infantile forms reported. Further, biallelic AGK pathogenic variants have also been identified in a familial case of non-syndromic isolated cataract (OMIM# 614691), expanding our understanding of the gene's influence beyond the originally defined syndrome. In this study, we provide a systematic review of molecularly confirmed cases with biallelic AGK pathogenic variants (Supplementary Table 1). Our analysis demonstrates the variable expressivity and penetrance of the central features of Sengers syndrome, as follows: cataracts (98%), cardiomyopathy (88%), lactic acidosis (adjusted 88%), and skeletal myopathy (adjusted 74%) (Table 1). Furthermore, we investigate the associations between genotype, biochemical profiles, and clinical outcomes, with a particular focus on infantile mortality. Our findings reveal that patients carrying homozygous nonsense variants have a higher incidence of infant mortality and a lower median age of death (p = 0.005 and p = 0.02, Table 2a). However, the location of pathogenic variants within the AGK domains was not significantly associated with infantile death (p = 0.62, Table 2b). Additionally, we observe a borderline association between the absence of lactic acidosis and longer survival (p = 0.053, Table 2c). Overall, our systematic review sheds light on the diverse clinical manifestations of AGK-related disorders and highlights potential factors that influence its prognosis. These provide important implications for the diagnosis, treatment, and counseling of affected individuals and families.

Cardiac Involvement in Mitochondrial Disorders

PURPOSE OF REVIEW

We review pathophysiology and clinical features of mitochondrial disorders manifesting with cardiomyopathy.

RECENT FINDINGS

Mechanistic studies have shed light into the underpinnings of mitochondrial disorders, providing novel insights into mitochondrial physiology and identifying new therapeutic targets. Mitochondrial disorders are a group of rare genetic diseases that are caused by mutations in mitochondrial DNA (mtDNA) or in nuclear genes that are essential to mitochondrial function. The clinical picture is extremely heterogeneous, the onset can occur at any age, and virtually, any organ or tissue can be involved. Since the heart relies primarily on mitochondrial oxidative metabolism to fuel contraction and relaxation, cardiac involvement is common in mitochondrial disorders and often represents a major determinant of their prognosis.

Long term follow-up in two siblings with Sengers syndrome: Case report

Background

Sengers syndrome is characterized by congenital cataract, hypertrophic cardiomyopathy, mitochondrial myopathy, and lactic acidosis associated with mutations in AGK gene. Clinical course ranges from a severe fatal neonatal form, to a more benign form allowing survival into adulthood, to an isolated form of congenital cataract. Thus far few reported cases have survived the second decade at their latest examination, and no natural history data are available for the disease.

Case presentation

Here we provide a 20-year follow-up in two siblings with a benign form of Sengers syndrome, expanding the phenotypical spectrum of the disease by reporting a condition of ovarian agenesis.

Conclusion

To our knowledge, this report provides the first longitudinal data of Sengers syndrome patients.

Supplementary information

The online version contains supplementary material available at 10.1186/s13052-022-01370-y.

Characterization of a Novel Splicing Variant in Acylglycerol Kinase (AGK) Associated with Fatal Sengers Syndrome

Mitochondrial functional integrity depends on protein and lipid homeostasis in the mitochondrial membranes and disturbances in their accumulation can cause disease. AGK, a mitochondrial acylglycerol kinase, is not only involved in lipid signaling but is also a component of the TIM22 complex in the inner mitochondrial membrane, which mediates the import of a subset of membrane proteins. AGK mutations can alter both phospholipid metabolism and mitochondrial protein biogenesis, contributing to the pathogenesis of Sengers syndrome. We describe the case of an infant carrying a novel homozygous AGK variant, c.518+1G>A, who was born with congenital cataracts, pielic ectasia, critical congenital dilated myocardiopathy, and hyperlactacidemia and died 20 h after birth. Using the patient’s DNA, we performed targeted sequencing of 314 nuclear genes encoding respiratory chain complex subunits and proteins implicated in mitochondrial oxidative phosphorylation (OXPHOS). A decrease of 96-bp in the length of the AGK cDNA sequence was detected. Decreases in the oxygen consumption rate (OCR) and the OCR:ECAR (extracellular acidification rate) ratio in the patient’s fibroblasts indicated reduced electron flow through the respiratory chain, and spectrophotometry revealed decreased activity of OXPHOS complexes I and V. We demonstrate a clear defect in mitochondrial function in the patient’s fibroblasts and describe the possible molecular mechanism underlying the pathogenicity of this novel AGK variant. Experimental validation using in vitro analysis allowed an accurate characterization of the disease-causing variant.

The First Cataract Surgeons in the British Isles

PURPOSE

To describe the entry of cataract surgery into the British Isles.

METHODS

Handbills, books, and other historical sources were reviewed to determine when cataract surgery was first performed in the region.

RESULTS

Roman artifacts suggest that couching was performed in the British Isles in antiquity. Seemingly miraculous cures of blindness during the early Middle Ages might be consistent with couching. However, there is no strong evidence of medieval cataract surgery in the region. Cataract couching probably arrived in England by the 1560s, in Scotland by 1595, in Ireland by 1684, and in Anglo-America by 1751. Before the 18th century, cataract surgery was taught within families, apprenticeships, and mountebank troupes. Beginning in the 17th century, congenital cataract surgery permitted surgeons to tout their skills and to explore visual perception. However, in some cases, such as the couching of the 13-year-old Daniel Dolins by surgeon William Cheselden in 1727, whether the cataracts were truly congenital, and whether vision improved in any way, remain in doubt. Beginning in the 1720s, cataract surgery began to be performed by traditional surgeons in hospitals. However, for most of the century, the highest-volume cataract surgeons continued to be itinerant oculists, including those who performed cataract extraction in the latter half of the century.

CONCLUSIONS

Cataract surgery might have been performed in Roman Britain. Specific evidence of cataract surgery emerges in the region in the Elizabethan era. Cataract extraction was performed in the British Isles by 1753, but couching remained popular throughout the 18th century. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Sengers syndrome: a rare case of cardiomyopathy combined with congenital cataracts in an infant: post-mortem case report

Sengers syndrome is a rare autosomal recessive disorder caused by a mutation in the Acylglycerol Kinase (AGK) gene with subsequent mitochondrial dysfunction. It is a combination of cardiomyopathy, skeletal myopathy, congenital bilateral cataracts, and lactic acidosis following exertion. The current study describes an extremely rare case of Sengers syndrome that is diagnosed during post-mortem examination. A four-month-old female child underwent sudden cardiac arrest immediately following the induction of general anesthesia for lens extraction surgery. This infant was the first child born to healthy, non-consanguineous, Egyptian parents. There were unremarkable medical problems either during pregnancy or during delivery. This infant was born at term with a normal APGAR score and weight. She had congenital bilateral cataracts since birth, easily-fatigued, and delayed milestones for her age. A post-mortem examination revealed a hypertrophied heart that weighed 96.6 grams with left ventricular hypertrophy. The left ventricle free wall thickness was 1cm, and an interventricular septum thickness of 1.3 cm. Histopathologically, the myocardium showed myocytes disarray. Also, the myocytes were hypertrophied, and vacuolated. The Gömöri trichrome stain revealed vacuolated cardiomyocytes surrounded by collagenous connective tissue, and the Periodic Acid Schiff (PAS) stain excluded that these vacuolations were related to glycogen storage disease. Focal lymphocytic infiltrations were observed within the myocardium. Thus, Sengers syndrome should be taken into consideration as a possible diagnosis whenever a congenital cataract is present for clinical and medicolegal cases.

Case Report: Two Chinese Infants of Sengers Syndrome Caused by Mutations in AGK Gene

Sengers syndrome (OMIM #212350) is a rare autosomal recessive disorder due to mutations in acylglycerol kinase (AGK) gene. We report two cases that were diagnosed clinically and confirmed genetically. Both infants had typical clinical features characterized by hypertrophic cardiomyopathy, bilateral cataracts, myopathy, and lactic acidosis, and heart failure was the most severe manifestation. Genetic testing of a boy revealed a homozygous pathogenic variant for Sengers syndrome in AGK (c.1131+2T>C) which was classified as likely pathogenic according to the ACMG guideline; besides, his skeletal muscle biopsy and transmission electron microscope presented obvious abnormity. One girl had compound heterozygous (c.409C>T and c.390G>A) variants of AGK gene that was identified in the proband and further Sanger sequencing indicated that the parents carried a single heterozygous mutation each. After the administration of "cocktail" therapy including coenzyme Q10, carnitine, and vitamin B complex, as well as ACEI, heart failure and myopathy of the boy were significantly improved and the condition was stable after 1-year follow-up, while the cardiomyopathy of the girl is not progressive but the plasma lactate acid increased significantly. We present the first report of two infants with Sengers syndrome diagnosed via exome sequencing in China.

Atypical Presentation of Sengers Syndrome: A Novel Mutation Revealed with Postmortem Genetic Testing

INTRODUCTION

Sengers syndrome is an autosomal recessive disorder characterized by congenital cataracts, hypertrophic cardiomyopathy, skeletal myopathy and lactic acidosis. The causative AGK mutations have been identified with whole exome sequencing.

CLINICAL REPORT

We report on a 9-month-old infant with episodic lactic acidosis who died before a definitive diagnosis could be established. Postmortem genomic autopsy revealed a novel homozygous NM_018238: c.1215dupG; p.Phe406Valfs*4 mutation in AGK (OMIM 610345) confirming the diagnosis of Sengers syndrome.

CONCLUSION

This report provides further evidence that reverse genetics is a useful approach in patients who do not manifest the hallmark features of known and recognizable syndromes.

Extending the phenotypic spectrum of Sengers syndrome: Congenital lactic acidosis with synthetic liver dysfunction

Sengers syndrome is a rare autosomal recessive mitochondrial disease characterized by lactic acidosis, hypertrophic cardiomyopathy and bilateral cataracts. We present here a case of neonatal demise, within the first day of life, who initially presented with severe lactic acidosis, with evidence of both chorioamnionitis and cardiogenic shock. Initial metabolic labs demonstrated a severe lactic acidosis prompting genetic testing which revealed a homozygous pathogenic variant for Sengers syndrome in AGK, c.979A >  T; p.K327^*. In addition to the canonical features of Sengers syndrome, our patient is the first reported case with liver dysfunction extending the phenotypic spectrum both in terms of severity and complications. This case also highlights the importance of maintaining a broad differential for congenital lactic acidosis.

Mutation in the AGK gene in two siblings with unusual Sengers syndrome

Sengers syndrome is a rare autosomal recessive metabolic disorder caused by lack of acylglycerol kinase due to mutations in the AGK gene. It is characterized by congenital cataract, hypertrophic cardiomyopathy, myopathy and lactic acidosis. Two clinical forms have been described: a severe neonatal form, and a more benign form displaying exercise intolerance. We describe two siblings with congenital cataract, cardiomyopathy, hypotonia, intellectual disability and lactic acidosis. Whole exome sequencing revealed a homozygous c.1035dup mutation in the two siblings, supporting a diagnosis of Sengers syndrome. Our patients presented an intermediate form with intellectual deficiency, an unusual feature in Sengers syndrome. This permitted a prenatal diagnosis for a following pregnancy.

Cardiomyopathies Due to Left Ventricular Noncompaction, Mitochondrial and Storage Diseases, and Inborn Errors of Metabolism

The normal function of the human myocardium requires the proper generation and utilization of energy and relies on a series of complex metabolic processes to achieve this normal function. When metabolic processes fail to work properly or effectively, heart muscle dysfunction can occur with or without accompanying functional abnormalities of other organ systems, particularly skeletal muscle. These metabolic derangements can result in structural, functional, and infiltrative deficiencies of the heart muscle. Mitochondrial and enzyme defects predominate as disease-related etiologies. In this review, left ventricular noncompaction cardiomyopathy, which is often caused by mutations in sarcomere and cytoskeletal proteins and is also associated with metabolic abnormalities, is discussed. In addition, cardiomyopathies resulting from mitochondrial dysfunction, metabolic abnormalities, storage diseases, and inborn errors of metabolism are described.

Potentially diagnostic electron paramagnetic resonance spectra elucidate the underlying mechanism of mitochondrial dysfunction in the deoxyguanosine kinase deficient rat model of a genetic mitochondrial DNA depletion syndrome

A novel rat model for a well-characterized human mitochondrial disease, mitochondrial DNA depletion syndrome with associated deoxyguanosine kinase (DGUOK) deficiency, is described. The rat model recapitulates the pathologic and biochemical signatures of the human disease. The application of electron paramagnetic (spin) resonance (EPR) spectroscopy to the identification and characterization of respiratory chain abnormalities in the mitochondria from freshly frozen tissue of the mitochondrial disease model rat is introduced. EPR is shown to be a sensitive technique for detecting mitochondrial functional abnormalities in situ and, here, is particularly useful in characterizing the redox state changes and oxidative stress that can result from depressed expression and/or diminished specific activity of the distinct respiratory chain complexes. As EPR requires no sample preparation or non-physiological reagents, it provides information on the status of the mitochondrion as it was in the functioning state. On its own, this information is of use in identifying respiratory chain dysfunction; in conjunction with other techniques, the information from EPR shows how the respiratory chain is affected at the molecular level by the dysfunction. It is proposed that EPR has a role in mechanistic pathophysiological studies of mitochondrial disease and could be used to study the impact of new treatment modalities or as an additional diagnostic tool.

CLPB variants associated with autosomal-recessive mitochondrial disorder with cataract, neutropenia, epilepsy, and methylglutaconic aciduria

3-methylglutaconic aciduria (3-MGA-uria) is a nonspecific finding associated with mitochondrial dysfunction, including defects of oxidative phosphorylation. 3-MGA-uria is classified into five groups, of which one, type IV, is genetically heterogeneous. Here we report five children with a form of type IV 3-MGA-uria characterized by cataracts, severe psychomotor regression during febrile episodes, epilepsy, neutropenia with frequent infections, and death in early childhood. Four of the individuals were of Greenlandic descent, and one was North American, of Northern European and Asian descent. Through a combination of homozygosity mapping in the Greenlandic individuals and exome sequencing in the North American, we identified biallelic variants in the caseinolytic peptidase B homolog (CLPB). The causative variants included one missense variant, c.803C>T (p.Thr268Met), and two nonsense variants, c.961A>T (p.Lys321*) and c.1249C>T (p.Arg417*). The level of CLPB protein was markedly decreased in fibroblasts and liver of affected individuals. CLPB is proposed to function as a mitochondrial chaperone involved in disaggregation of misfolded proteins, resulting from stress such as heat denaturation.

Disorders of phospholipid metabolism: an emerging class of mitochondrial disease due to defects in nuclear genes

The human nuclear and mitochondrial genomes co-exist within each cell. While the mitochondrial genome encodes for a limited number of proteins, transfer RNAs, and ribosomal RNAs, the vast majority of mitochondrial proteins are encoded in the nuclear genome. Of the multitude of mitochondrial disorders known to date, only a fifth are maternally inherited. The recent characterization of the mitochondrial proteome therefore serves as an important step toward delineating the nosology of a large spectrum of phenotypically heterogeneous diseases. Following the identification of the first nuclear gene defect to underlie a mitochondrial disorder, a plenitude of genetic variants that provoke mitochondrial pathophysiology have been molecularly elucidated and classified into six categories that impact: (1) oxidative phosphorylation (subunits and assembly factors); (2) mitochondrial DNA maintenance and expression; (3) mitochondrial protein import and assembly; (4) mitochondrial quality control (chaperones and proteases); (5) iron–sulfur cluster homeostasis; and (6) mitochondrial dynamics (fission and fusion). Here, we propose that an additional class of genetic variant be included in the classification schema to acknowledge the role of genetic defects in phospholipid biosynthesis, remodeling, and metabolism in mitochondrial pathophysiology. This seventh class includes a small but notable group of nuclear-encoded proteins whose dysfunction impacts normal mitochondrial phospholipid metabolism. The resulting human disorders present with a diverse array of pathologic consequences that reflect the variety of functions that phospholipids have in mitochondria and highlight the important role of proper membrane homeostasis in mitochondrial biology.

Sengers syndrome: six novel AGK mutations in seven new families and review of the phenotypic and mutational spectrum of 29 patients

Background

Sengers syndrome is an autosomal recessive condition characterized by congenital cataract, hypertrophic cardiomyopathy, skeletal myopathy and lactic acidosis. Mutations in the acylglycerol kinase (AGK) gene have been recently described as the cause of Sengers syndrome in nine families.

Methods

We investigated the clinical and molecular features of Sengers syndrome in seven new families; five families with the severe and two with the milder form.

Results

Sequence analysis of AGK revealed compound heterozygous or homozygous predicted loss-of-function mutations in all affected individuals. A total of eight different disease alleles were identified, of which six were novel, homozygous c.523_524delAT (p.Ile175Tyrfs*2), c.424-1G > A (splice site), c.409C > T (p.Arg137*) and c.877 + 3G > T (splice site), and compound heterozygous c.871C > T (p.Gln291*) and c.1035dup (p.Ile346Tyrfs*39). All patients displayed perinatal or early-onset cardiomyopathy and cataract, clinical features pathognomonic for Sengers syndrome. Other common findings included blood lactic acidosis and tachydyspnoea while nystagmus, eosinophilia and cervical meningocele were documented in only either one or two cases. Deficiency of the adenine nucleotide translocator was found in heart and skeletal muscle biopsies from two patients associated with respiratory chain complex I deficiency. In contrast to previous findings, mitochondrial DNA content was normal in both tissues.

Conclusion

We compare our findings to those in 21 previously reported AGK mutation-positive Sengers patients, confirming that Sengers syndrome is a clinically recognisable disorder of mitochondrial energy metabolism.

Lack of the mitochondrial protein acylglycerol kinase causes Sengers syndrome

Exome sequencing of an individual with congenital cataracts, hypertrophic cardiomyopathy, skeletal myopathy, and lactic acidosis, all typical symptoms of Sengers syndrome, discovered two nonsense mutations in the gene encoding mitochondrial acylglycerol kinase (AGK). Mutation screening of AGK in further individuals with congenital cataracts and cardiomyopathy identified numerous loss-of-function mutations in an additional eight families, confirming the causal nature of AGK deficiency in Sengers syndrome. The loss of AGK led to a decrease of the adenine nucleotide translocator in the inner mitochondrial membrane in muscle, consistent with a role of AGK in driving the assembly of the translocator as a result of its effects on phospholipid metabolism in mitochondria.

The mitochondrial disulfide relay system protein GFER is mutated in autosomal-recessive myopathy with cataract and combined respiratory-chain deficiency

A disulfide relay system (DRS) was recently identified in the yeast mitochondrial intermembrane space (IMS) that consists of two essential components: the sulfhydryl oxidase Erv1 and the redox-regulated import receptor Mia40. The DRS drives the import of cysteine-rich proteins into the IMS via an oxidative folding mechanism. Erv1p is reoxidized within this system, transferring its electrons to molecular oxygen through interactions with cytochrome c and cytochrome c oxidase (COX), thereby linking the DRS to the respiratory chain. The role of the human Erv1 ortholog, GFER, in the DRS has been poorly explored. Using homozygosity mapping, we discovered that a mutation in the GFER gene causes an infantile mitochondrial disorder. Three children born to healthy consanguineous parents presented with progressive myopathy and partial combined respiratory-chain deficiency, congenital cataract, sensorineural hearing loss, and developmental delay. The consequences of the mutation at the level of the patient's muscle tissue and fibroblasts were 1) a reduction in complex I, II, and IV activity; 2) a lower cysteine-rich protein content; 3) abnormal ultrastructural morphology of the mitochondria, with enlargement of the IMS space; and 4) accelerated time-dependent accumulation of multiple mtDNA deletions. Moreover, the Saccharomyces cerevisiae erv1(R182H) mutant strain reproduced the complex IV activity defect and exhibited genetic instability of the mtDNA and mitochondrial morphological defects. These findings shed light on the mechanisms of mitochondrial biogenesis, establish the role of GFER in the human DRS, and promote an understanding of the pathogenesis of a new mitochondrial disease.

Neuroradiologic findings in Sengers syndrome

Sengers syndrome is characterized by a constellation of congenital cataracts, hypertrophic cardiomyopathy, skeletal myopathy, and lactic acidosis. Two forms of the disease have been described: a fatal neonatal form, and a more benign form in which patients live into their second or third decades. With the exception of time to death, no findings have distinguished these two forms. We present 3 cases of neonatal Sengers syndrome with significant central nervous system involvement, a finding not previously described. We suggest that the fatal neonatal form of Sengers syndrome would be more accurately described as a mitochondrial encephalomyopathy. Cranial imaging may help distinguish the two types of this syndrome.

Mitochondrial encephalomyopathy associated with diabetes mellitus, cataract, and corpus callosum atrophy

A 44-year-old woman with mitochondrial encephalomyopathy noticed weakness of the lower extremities at the age of 30 years. She also has type 2 diabetes mellitus, posterior subcapsular cataracts in both eyes, and corpus callosum atrophy. Family history showed that a maternal cousin had a myopathy, 3 maternal aunts had diabetes mellitus, and her mother and 2 maternal aunts had cataracts. External ophthalmoplegia, proximal myopathy, and absent deep tendon reflexes were noted. The mitochondrial DNA 3243 point mutation was negative. Muscle biopsy showed ragged-red fibers, cytochrome c oxidase (COX)-positive fibers, and COX-negative fibers.

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

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.

Sengers disease: a rare association of hypertrophic cardiomyopathy and congenital cataracts

Hypertrophic cardiomyopathy is an uncommon childhood cardiac disease and can be primary or secondary. Several systemic diseases are known to be associated with this entity. Senger's disease is a mitochondrial disorder causing congenital cataracts lactic acidosis and skeletal and cardiac myopathy. Diagnosis should be kept in mind when routine neonatal eye screening reveals absent red reflex. The authors report a case of Sengers disease and discuss the underlying pathogenetic mechanisms.

Adenine nucleotide translocator 1 deficiency associated with Sengers syndrome

Sengers syndrome is characterized by congenital cataracts, hypertrophic cardiomyopathy, mitochondrial myopathy, and lactic acidosis, but no abnormalities have been found with routine mitochondrial biochemical diagnostics (the determination of pyruvate oxidation rates and enzyme measurements). In immunoblot analysis, the protein content of the mitochondrial adenine nucleotide translocator 1 (ANT1) was found to be strongly reduced in the muscle tissues of two unrelated patients with Sengers syndrome. In addition, low residual adenine nucleotide translocator activity was detected upon the reconstitution of detergent-solubilized mitochondrial extracts from the patients' skeletal or heart muscle into liposomes. Sequence analysis and linkage analysis showed that ANT1 was not the primary genetic cause of Sengers syndrome. We propose that transcriptional, translational, or posttranslational events are responsible for the ANT1 deficiency associated with the syndrome.

Inborn errors of metabolism around time of birth

Inborn errors of metabolism commonly present around the time of birth. Although most affected babies are born healthy and subsequently deteriorate, some disorders may present at (or shortly after) birth and a few may be detected by antenatal ultrosonography. In many cases, it is important that the diagnosis is made quickly and a strategy to identify those at high risk is proposed. Treatment should not be delayed for a definitive diagnosis.

Each mammalian mitochondrial outer membrane porin protein is dispensable: effects on cellular respiration

Voltage-dependent anion channels (VDACs, also known as mitochondrial porins) are small pore-forming proteins of the mitochondrial outer membrane found in all eukaryotes. Mammals harbor three distinct VDAC isoforms, with each protein sharing 65-70% sequence identity. Deletion of the yeast VDAC1 gene leads to conditional lethality that can be partially or completely complemented by the mammalian VDAC genes. In vitro, VDACs conduct a variety of small metabolites and in vivo they serve as a binding site for several cytosolic kinases involved in intermediary metabolism, yet the specific physiologic role of each isoform is unknown. Here we show that mouse embryonic stem cells lacking each isoform are viable but exhibit a 30% reduction in oxygen consumption. VDAC1 and VDAC2 deficient cells exhibit reduced cytochrome c oxidase activity, whereas VDAC3 deficient cells have normal activity. These results indicate that VDACs are not essential for cell viability and we speculate that reduced respiration in part reflects decreased outer membrane permeability for small metabolites necessary for oxidative phosphorylation.

Merosin-positive congenital muscular dystrophy in two siblings with cataract and slight mental retardation

We report on two siblings that have been followed for 14 years, with merosin-positive congenital muscular dystrophy (CMD), cataract, retinitis pigmentosa, dysversion of the optic disc, but no cerebral anomalies, except for microcephaly and slight mental retardation (MR). The younger child had three generalized seizures easily controlled by anticonvulsant therapy. Both children presented hypotonia from birth, delayed psychomotor development, generalized muscular weakness, and atrophy and joint contractures of knees and ankles. The course of the disease, apparently static during the first 10 years of life, became progressive during the second decade with loss of deambulation by the age of 13. Creatine kinase was increased in both children. Bilateral cataract was diagnosed at 6-months of age. In spite of the occurrence of microcephaly, MR was slight and the siblings acquired reading and writing skills after the aged 10. Head magnetic resonance imaging showed normal results in both siblings. The classification of these cases within the broad spectrum of CMD is difficult since most of the known muscle-eye-brain syndromes generally show severe MR and brain anomalies. We consider these cases as corresponding to the rarer syndromes of merosin-positive CMD with associated features such as cataract and MR that were particularly emphasized during the 50th ENMC International Workshop on CMD [Dubowitz V. Workshop report: 50th ENMC International workshop on congenital muscular dystrophy. Neuromusc Disord 1997;7:539-547]. Further genetic, pathological, neuroradiological, and immunocytochemical studies will be necessary for better elucidation of the classification and pathogenesis of CMD.

Bilateral infantile cataractogenesis in a patient with deficiency of complex I, a mitochondrial electron transport chain enzyme

Progressive bilateral cataracts developed in infancy in a 5-month-old girl with deficiency of complex I, a mitochondrial electron transport chain enzyme. In the newborn period, she had severe lactic acidosis and the diagnosis of complex I deficiency was confirmed by mitochondrial respiratory chain assay on muscle biopsy. By 5 months, she had completely opaque nuclear sclerotic cataracts, with loss of fixation and the red reflex. She underwent bilateral, sequential cataract extraction. The lens aspirate was submitted for cytologic analysis and electron microscopy, which revealed increased intracellular glycogen and swollen mitochondria. To our knowledge the association of complex I deficiency with cataracts in infancy has not been reported previously. The diagnosis of a respiratory chain enzyme defect in infancy is an indication for early ophthalmic evaluation to identify cataracts that may result in visual loss. Conversely, the recognition of cataracts in infants with unexplained neurologic disease or metabolic acidosis may necessitate further evaluation for metabolic etiologies, including mitochondrial disorders.

Cardiac transplantation for hypertrophic cardiomyopathy associated with Sengers syndrome

Sengers' syndrome is a rare condition consisting of congenital cataracts, mitochondrial myopathy, and hypertrophic cardiomyopathy. The syndrome is transmitted in an autosomal recessive pattern. Progressive cardiac failure is the cause of death in most patients. This report describes cardiac transplantation for the treatment of the cardiomyopathy associated with Sengers' syndrome.

Myopathy, lactic acidosis, and sideroblastic anemia: a new syndrome

We describe 2 sibs (brother and sister) with myopathy, sideroblastic anemia, lactic acidosis, mental retardation, microcephaly, high palate, high philtrum, distichiasis, and micrognathia. Very low levels of cytochromes a, b, and c were detected in the patients' muscle mitochondria. Deposition of iron within the mitochondria of bone marrow erythroblasts was observed on electron microscopy. Irregular and enlarged mitochondria with paracrystalline inclusions were also seen on electron microscopy of the patients' muscle specimen. Examination of DNA from the affected sibs showed no deletions in the mitochondrial DNA nor the mutations identified in the syndromes of mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS) or myoclonus, and epilepsy associated with rugged-red fibers (MERRF). Since the parents were first cousins and 2 of 6 sibs (male and female) were affected, we suggest that the syndrome expressed by our patients represents a previously unknown autosomal recessive disorder that includes mitochondrial myopathy, lactic acidosis, and sideroblastic anemia.