Leigh syndrome caused by mitochondrial DNA-maintenance defects revealed by whole exome sequencing

Diagnosis of Inherited Metabolic Disease in Older Patients: A Systematic Literature Review

Inherited metabolic diseases (IMDs) are genetic disorders that disrupt biochemical processes in the human body, due to pathogenic variants in genes encoding enzymes or transporters. While IMDs are mostly diagnosed in infancy or childhood, there is an increasing number of diagnoses in adult patients. Delayed diagnosis, particularly in older patients, may reflect the diagnostic odyssey usually observed in rare diseases' patients and can result in complications and reduced quality of life for patients and their families. The aim of the study was to better characterize the diagnosis of IMDs in older patients (≥ 65 years). We conducted a systematic literature review (SLR) to examine the diagnosis and clinical presentation of IMDs in patients aged 65 and older. We searched databases like PubMed, Embase, and Lilacs for relevant studies from 1965 to 2023. A total of 260 articles were included, representing 293 patients with a median age of 69 years at diagnosis. From this SLR, 67 different diagnoses have been reported. The most frequently reported diseases were Fabry disease, alkaptonuria, Gaucher disease, mitochondrial disorders, and glycogen storage disease type V. Median diagnostic delay was 14.5 years with a wide range of 1-91 years. Musculoskeletal symptoms were the most frequently reported, followed by neurological and cardiovascular symptoms. Our findings underscore the importance of recognizing IMDs in older patients and the need for awareness among healthcare providers to improve diagnosis and patient care. Future guidelines and teaching programs should incorporate metabolic investigations for older patients presenting with symptoms suggestive of IMDs.

A decade of whole-exome sequencing in Brazilian Neurology: from past insights to future perspectives

Over the last decade, whole-exome sequencing (WES) has become a standard diagnostic tool, significantly transforming the landscape of clinical genetics and playing a pivotal role in the diagnosis of neurogenetic diseases. This revolutionary shift has left a lasting impact on the field of neurology in Brazil. The current review article examines key developments and milestones achieved in Brazil through the application of WES in neurology and discusses forthcoming challenges and essential steps to advance molecular diagnosis. Several studies report the use of WES to diagnose genetic disorders with neurological manifestations in Brazil, underscoring the growing importance of molecular diagnosis in neurogenetics. These studies often provide detailed phenotypic analyses and clinical descriptions, offering valuable insights into the genetic underpinnings of several neurological conditions. Many reports highlight the use of WES in the investigation of complex neurological conditions in Brazil, such as neurodevelopmental disorders, hereditary spastic paraplegia, movement disorders, and ataxia. The discovery of new genes implicated in monogenic diseases with neurological manifestations through WES was a significant breakthrough. Despite these advances, the availability of large cohort studies on rare diseases in Brazil remains limited, hindering the ability to generalize findings and explore the full spectrum of genetic diversity. However, a few larger cohort studies have substantially contributed to our understanding of rare diseases and specific neurological disorders.While WES has limitations and may eventually be supplanted by more advanced diagnostic tools, it left a permanent mark on the neurology field in Brazil. The field of neurogenetics is set to become increasingly important in the future.

A Comprehensive Approach to the Diagnosis of Leigh Syndrome Spectrum

BACKGROUND

Leigh syndrome spectrum (LSS) is a novel nomenclature that encompasses both classical Leigh syndrome and Leigh-like phenotypes. Given the heterogeneity of disease presentation, a new consensus published recently addressed the main issues and proposed general guidelines towards diagnosis. Based on these recommendations, we developed a simple pipeline that can be useful in the diagnosis of LSS.

METHODS

We combined previously published criteria with our own experience to achieve a diagnostic framework that can provide faster satisfactory results with fewer resources.

RESULTS

We suggest adding basic biochemical tests for amino acids, acylcarnitine, and urinary organic acids as parallel investigations, as these results can be obtained in a short time. This approach characterized 80% of our cohort and promoted specific intervention in 10% of confirmed cases.

CONCLUSIONS

Genetic studies are crucial in the diagnosis of LSS, but they are time-consuming and might delay tailored interventions. Therefore, we suggest adding more affordable and less complex biochemical studies as primary tests when investigating treatable causes of LSS.

Leigh syndrome

Leigh syndrome, or subacute necrotizing encephalomyelopathy, was initially recognized as a neuropathological entity in 1951. Bilateral symmetrical lesions, typically extending from the basal ganglia and thalamus through brainstem structures to the posterior columns of the spinal cord, are characterized microscopically by capillary proliferation, gliosis, severe neuronal loss, and relative preservation of astrocytes. Leigh syndrome is a pan-ethnic disorder usually with onset in infancy or early childhood, but late-onset forms occur, including in adult life. Over the last six decades it has emerged that this complex neurodegenerative disorder encompasses more than 100 separate monogenic disorders associated with enormous clinical and biochemical heterogeneity. This chapter discusses clinical, biochemical and neuropathological aspects of the disorder, and postulated pathomechanisms. Known genetic causes, including defects of 16 mitochondrial DNA (mtDNA) genes and approaching 100 nuclear genes, are categorized into disorders of subunits and assembly factors of the five oxidative phosphorylation enzymes, disorders of pyruvate metabolism and vitamin and cofactor transport and metabolism, disorders of mtDNA maintenance, and defects of mitochondrial gene expression, protein quality control, lipid remodeling, dynamics, and toxicity. An approach to diagnosis is presented, together with known treatable causes and an overview of current supportive management options and emerging therapies on the horizon.

Spinal Cord Involvement in Adult Mitochondrial Diseases: A Cohort Study

The central nervous system is metabolically very demanding and consequently vulnerable to defects of the mitochondrial respiratory chain. While the clinical manifestations and the corresponding radiological findings of the brain involvement in mitochondrial diseases (e.g., stroke-like episodes, signal changes of the basal ganglia, cerebral and cerebellar atrophy) are well known, at present there are few data on the spinal-cord abnormalities in these pathologies, in particular in adult subjects. In this study, we present a cross-sectional cohort study on the prevalence and characterization of spinal-cord involvement in adult patients with genetically defined mitochondrial diseases.

Molecular basis of Leigh syndrome: a current look

Leigh Syndrome (OMIM 256000) is a heterogeneous neurologic disorder due to damage in mitochondrial energy production that usually starts in early childhood. The first description given by Leigh pointed out neurological symptoms in children under 2 years and premature death. Following cases brought some hypothesis to explain the cause due to similarity to other neurological diseases and led to further investigation for metabolic diseases. Biochemical evaluation and specific metabolic profile suggested impairment in energy production (OXPHOS) in mitochondria. As direct approach to involved tissues is not always possible or safe, molecular analysis is a great cost-effective option and, besides biochemical results, is required to confirm the underlying cause of this syndrome face to clinical suspicion. The Next Generation Sequencing (NGS) advance represented a breakthrough in molecular biology allowing simultaneous gene analysis giving short-time results and increasing the variants underlying this syndrome, counting over 75 monogenic causes related so far. NGS provided confirmation of emerging cases and brought up diagnosis in atypical presentations as late-onset cases, which turned Leigh into a heterogeneous syndrome with variable outcomes. This review highlights clinical presentation in both classic and atypical phenotypes, the investigation pathway throughout confirmation emphasizing the underlying genetic heterogeneity and increasing number of genes assigned to this syndrome as well as available treatment.