Case Report: Two Families With HPDL Related Neurodegeneration

HPDL Variant Type Correlates With Clinical Disease Onset and Severity

OBJECTIVE

Recently, a mitochondrial encephalopathy due to biallelic HPDL variants was described, associated with a broad range of clinical manifestations ranging from severe, infantile-onset neurodegeneration to adolescence-onset hereditary spastic paraplegia. HPDL converts 4-hydroxyphenylpyruvate acid (4-HPPA) into 4-hydroxymandelate (4-HMA), necessary for the synthesis of the mitochondrial electron transporter CoQ10. This suggests a possible bypass of the metabolic block by 4-HMA treatment; however, genotype-phenotype correlations are lacking.

METHODS

We established an HPDL Patient Registry to prepare for a future clinical trial. Here we report the clinical features of 13 enrolled participants and compare them with 86 previously reported patients. We establish three major clinical classes: severe, intermediate, and mild, presenting onset in early infancy, childhood, and adolescence, respectively. The biallelic genotypes were classified into truncating/truncating, truncating/missense, and missense/missense variants, mapped onto the predicted 3D protein structure, and correlated with severity.

RESULTS

Patients with biallelic truncating variants presented with severe phenotypes and earlier ages of onset. Missense variants were often associated with milder phenotypes, except those with variants predominantly located in or near the VOC2 domain containing iron-binding sites or the C-terminus, which had more severe phenotypes. In addition, p.Met1? variants were also correlated with more severe phenotypes.

INTERPRETATION

This study demonstrates the correlation of age of onset and disease severity with genotype for HPDL-related conditions. Patients with truncating variants and specific missense variants correlated with severe, early-onset features, whereas the presence of at least one missense variant located outside of the iron-binding sites correlated with milder presentations.

TRIAL REGISTRATION

Clinicaltrials.gov HPDL registry: https://clinicaltrials.gov/study/NCT05848271.

Quantitative natural history modeling of HPDL-related disease based on cross-sectional data reveals genotype-phenotype correlations

PURPOSE

Biallelic HPDL variants have been identified as the cause of a progressive childhood-onset movement disorder, with a broad clinical spectrum from severe neurodevelopmental disorder to juvenile-onset pure hereditary spastic paraplegia type 83. This study aims at delineating the geno- and phenotypic spectra of patients with HPDL-related disease, quantitatively modeling the natural history, and uncovering genotype-phenotype associations.

METHODS

A cross-sectional analysis of 90 published and 1 novel case was performed, using a Human-Phenotype-Ontology-based approach. Unsupervised phenotypic clustering was used alongside in silico analyses to identify distinct patient subgroups.

RESULTS

The study models the natural history of the HPDL-related disease in a global cohort, clarifying the molecular and phenotypic spectrum and identifying 3 distinct subgroups characterized by differences in onset, clinical trajectories, and survival. It establishes genotype-phenotype associations, showing that the presence of moderately pathogenic missense variants in 1 allele leads to a milder, spastic paraplegic phenotype with later disease onset, whereas biallelic, highly pathogenic missense or truncating variants are associated with a more severe phenotype and reduced life span.

CONCLUSION

Quantitative and unbiased natural history modeling in HPDL-related disease reveals significant genotype-phenotype associations, providing a foundation for variant interpretation, anticipatory guidance, and choice of outcome measures in future prospective and functional studies.

A novel homozygous HPDL variant in Japanese siblings with autosomal recessive hereditary spastic paraplegia: case report and literature review

Biallelic variants of 4-hydroxyphenylpyruvate dioxygenase-like (HPDL) gene have been linked to neurodegenerative disorders ranging from severe neonatal encephalopathy to early-onset spastic paraplegia. We identified a novel homozygous variant, c.340G > T (p.Gly114Cys), in the HPDL gene in two siblings with autosomal recessive hereditary spastic paraplegia (HSP). Despite sharing the same likely pathogenic variant, the older sister had pure HSP, whereas her brother had severe and complicated HSP, accompanied by early-onset mental retardation and abnormalities in magnetic resonance imaging. Given the clinical heterogeneity and potential for treatable conditions in HPDL-related diseases, we emphasize the importance of genetic testing for the HPDL gene.

Machine Learning Analysis of Alzheimer's Disease Single-Cell RNA-Sequencing Data across Cortex and Hippocampus Regions

Advancements in molecular biology have revolutionized our understanding of complex diseases, with Alzheimer's disease being a prime example. Single-cell sequencing, currently the most suitable technology, facilitates profoundly detailed disease analysis at the cellular level. Prior research has established that the pathology of Alzheimer's disease varies across different brain regions and cell types. In parallel, only machine learning has the capacity to address the myriad challenges presented by such studies, where the integration of large-scale data and numerous experiments is required to extract meaningful knowledge. Our methodology utilizes single-cell RNA sequencing data from healthy and Alzheimer's disease (AD) samples, focused on the cortex and hippocampus regions in mice. We designed three distinct case studies and implemented an ensemble feature selection approach through machine learning, also performing an analysis of distinct age-related datasets to unravel age-specific effects, showing differential gene expression patterns within each condition. Important evidence was reported, such as enrichment in central nervous system development and regulation of oligodendrocyte differentiation between the hippocampus and cortex of 6-month-old AD mice as well as regulation of epinephrine secretion and dendritic spine morphogenesis in 15-month-old AD mice. Our outcomes from all three of our case studies illustrate the capacity of machine learning strategies when applied to single-cell data, revealing critical insights into Alzheimer's disease.

Primary Coenzyme Q10 Deficiency: An Update

Coenzyme Q10 (CoQ10) has a number of vital functions in all cells, both mitochondrial and extra-mitochondrial. In addition to its key role in mitochondrial oxidative phosphorylation, CoQ10 serves as a lipid soluble antioxidant and plays an important role in fatty acid beta-oxidation and pyrimidine and lysosomal metabolism, as well as directly mediating the expression of a number of genes, including those involved in inflammation. Due to the multiplicity of roles in cell function, it is not surprising that a deficiency in CoQ10 has been implicated in the pathogenesis of a wide range of disorders. CoQ10 deficiency is broadly divided into primary and secondary types. Primary CoQ10 deficiency results from mutations in genes involved in the CoQ10 biosynthetic pathway. In man, at least 10 genes are required for the biosynthesis of functional CoQ10, a mutation in any one of which can result in a deficit in CoQ10 status. Patients may respond well to oral CoQ10 supplementation, although the condition must be recognised sufficiently early, before irreversible tissue damage has occurred. In this article, we have reviewed clinical studies (up to March 2023) relating to the identification of these deficiencies, and the therapeutic outcomes of CoQ10 supplementation; we have attempted to resolve the disparities between previous review articles regarding the usefulness or otherwise of CoQ10 supplementation in these disorders. In addition, we have highlighted several of the potential problems relating to CoQ10 supplementation in primary CoQ10 deficiency, as well as identifying unresolved issues relating to these disorders that require further research.

Neuroimaging in Primary Coenzyme-Q10-Deficiency Disorders

Coenzyme Q10 (CoQ10) is an endogenously synthesized lipid molecule. It is best known for its role as a cofactor within the mitochondrial respiratory chain where it functions in electron transfer and ATP synthesis. However, there are many other cellular pathways that also depend on the CoQ10 supply (redox homeostasis, ferroptosis and sulfide oxidation). The CoQ10 biosynthesis pathway consists of several enzymes, which are encoded by the nuclear DNA. The majority of these enzymes are responsible for modifications of the CoQ-head group (benzoquinone ring). Only three enzymes (PDSS1, PDSS2 and COQ2) are required for assembly and attachment of the polyisoprenoid side chain. The head-modifying enzymes may assemble into resolvable domains, representing COQ complexes. During the last two decades, numerous inborn errors in CoQ10 biosynthesis enzymes have been identified. Thus far, 11 disease genes are known (PDSS1, PDSS2, COQ2, COQ4, COQ5, COQ6, COQ7, COQ8A, COQ8B, COQ9 and HPDL). Disease onset is highly variable and ranges from the neonatal period to late adulthood. CoQ10 deficiency exerts detrimental effects on the nervous system. Potential consequences are neuronal death, neuroinflammation and cerebral gliosis. Clinical features include encephalopathy, regression, movement disorders, epilepsy and intellectual disability. Brain magnetic resonance imaging (MRI) is the most important tool for diagnostic evaluation of neurological damage in individuals with CoQ10 deficiency. However, due to the rarity of the different gene defects, information on disease manifestations within the central nervous system is scarce. This review aims to provide an overview of brain MRI patterns observed in primary CoQ10 biosynthesis disorders and to highlight disease-specific findings.