Aug 2026· Biomolecules· Vol 16, pp. 1164· 0 citations· 57 references
Medicine
TL;DR
This temporal dissociation reflects differential tissue vulnerability to intracellular ATP/GTP and NAD+ depletion caused by the primary enzymatic defect, and represents a continuous PRPS1-related neurometabolic spectrum.
Abstract
Loss-of-function (LoF) variants in the PRPS1 gene, encoding the phosphoribosyl pyrophosphate (PRPP) synthetase 1 enzyme, cause rare neurometabolic disorders historically viewed as discrete entities: nonsyndromic deafness (DFNX1), Charcot–Marie–Tooth disease type X5 (CMTX5), and Arts syndrome. A major clinical challenge is the temporal dissociation between early auditory failure and subsequent neurodegeneration, causing fragmented diagnostics. We systematically quantified this diagnostic latency and reconceptualized the disease spectrum through a molecular lens. A PRISMA-compliant systematic review identified 19 patients with genetically confirmed PRPS1 LoF variants, including our index case (c.362C>G) presenting a 15-year diagnostic delay. Kaplan–Meier analysis revealed sensorineural hearing loss manifested acutely (median 0 years; 95% CI: 0–1). In contrast, neurological deficits demonstrated a prolonged latency (median 3 years; 95% CI: 1–8), followed by ophthalmological signs (median 11.5 years). The median symptomatic delay was 3 years (range up to 19). We posit that this temporal dissociation reflects differential tissue vulnerability to intracellular ATP/GTP and NAD+ depletion caused by the primary enzymatic defect. Ultimately, DFNX1, CMTX5, and Arts syndrome represent a continuous PRPS1-related neurometabolic spectrum. Because targeted metabolic interventions (such as S-adenosylmethionine or nicotinamide riboside) have limited efficacy on advanced structural nerve damage, recognizing this early diagnostic window to initiate biochemical rescue prior to irreversible axonal degeneration is critical.
PPP1R21-related neurodevelopmental disorder (PPP1R21-NDD) is an ultra-rare autosomal-recessive encephalopathy caused by dysfunction of the Five-subunit Endosomal Rab5 and RNA/ribosome intermediarY (FERRY) complex. To delineate the clinical, neuroimaging, and molecular spectrum of PPP1R21-NDD and outline diagnostic and research priorities. Targeted searches of PubMed, EMBASE, Scopus, Web of Science, and Google Scholar through January 2026 were performed. Eligible reports included molecularly confirmed biallelic PPP1R21 cases and related functional studies. Two researchers independently extracted individual-level data following narrative review quality criteria. Twenty-five individuals from 21 families harbored 17 distinct variants (15 loss-of-function, 2 missense), all homozygous, reflecting high consanguinity. Profound global developmental delay/intellectual disability was universal; hypotonia near-universal (22/25, 88%). Ambulation was delayed and ataxic when achieved; expressive language was minimal or absent. A recognizable coarse facial gestalt was observed with thick eyebrows, broad nasal bridge, thick lips, and low-set ears. Systemic features included feeding dysfunction and respiratory morbidity requiring gastrostomy or tracheostomy in severe cases. Mortality was 17% (4/24). Neuroimaging showed callosal thinning, white-matter volume loss, ventricular enlargement, and vermian hypoplasia. Patient fibroblasts showed delayed transferrin clearance and elevated proteasome activity, suggesting endosomal dysfunction and proteasome hyperactivation. PPP1R21-NDD is a severe recessive encephalopathy with a convergent phenotype and evidence of endo-lysosomal dysfunction. Diagnosis should be pursued with exome or genome sequencing in patients with characteristic clinical and neuroimaging features, particularly in consanguineous families. Research priorities include natural history studies, standardized magnetic resonance imaging (MRI) protocols, neural disease models, and therapeutic strategies targeting endosomal trafficking.
F. Comisi, G. Di Pasquale, A. Comisi et al.· Neurogenetics· 0 citations
UBTF-related CONDBA presents with early normal or mildly delayed development followed by regression and progressive ataxia, and elevated NFL may serve as a biomarker of neuronal injury in both humans and animal models.
A. Nagy, A. Luddy, Francine Molay et al.· Journal of Medical Genetics· 0 citations
W Whole exome sequencing revealed a homozygous splice‐site variant (c.454+3A>G) in the TRAPPC4 gene, confirming the diagnosis of NEDESBA, and emphasizes the critical role of early molecular testing in achieving a precise diagnosis.
Anil Kumar, Ajay Kumar, Arvinder Wander et al.· International Journal of Dev...· 0 citations
Hypotonia, Ataxia, Developmental Delay, and Tooth Enamel Defect Syndrome (HADDTS; OMIM #617915) is an ultra-rare autosomal dominant disorder caused by predominantly de novo pathogenic variants in CTBP1, encoding a NAD(H)-dependent transcriptional corepressor. We reviewed all HADDTS cases reported from database inception to July 2026, searching PubMed/MEDLINE, Google Scholar, ClinVar, DECIPHER, OMIM, preprint servers, and the HADDTS Foundation, identifying 25 peer-reviewed cases from at least 11 countries; registries indicate at least 50 known individuals. Global developmental delay and language impairment were universal (25/25, 100%), followed by intellectual disability (24/25, 96%), hypotonia (22/25, 88%), ataxia and enamel defects (19/25, 76% each), cerebellar atrophy (18/25, 72%), feeding difficulties (15/25, 60%), myopathy (15/25, 60%), regression (10/25, 40%), oculomotor apraxia (7/25, 28%), scoliosis (6/25, 24%), respiratory chain dysfunction (5/25, 20%), skeletal anomalies (4/25, 16%), and seizures (2/25, 8%). The recurrent p.Arg342Trp (NM_001328.2; p.Arg331Trp, MANE Select NM_001012614.2) accounts for 84%, with severity from mild impairment to profound disability. In all four non-recurrent-variant carriers the canonical tetrad was incomplete; seizures and classifying skeletal anomalies occurred only in that group. Mutant CTBP1 acts dominant-negatively and heterodimerises with the essential paralog CTBP2, explaining the multisystem severity. HADDTS is a neurodevelopmental-mitochondrial overlap disorder; registries, mitochondrial evaluation, and allele-specific therapies are priorities.
E. Akdaş, Dingyu Lu, Linshen Zhang et al.· International Journal of Mol...· 0 citations
TDP-43 proteinopathies, encompassing amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD), and limbic-predominant age-related TDP-43 encephalopathy (LATE), represent a heterogeneous spectrum of devastating neurodegenerative disorders. For decades, the diverse clinical presentations of these diseases have complicated antemortem diagnosis and hindered the development of disease-modifying therapies. However, recent breakthroughs in basic science are beginning to address these clinical barriers, although substantial hurdles to practical clinical application remain. Structural elucidation via cryo-electron microscopy (Cryo-EM) has shattered the single-protein amyloid dogma by revealing that TDP-43 can form hetero-amyloid filaments with ANXA11, thereby providing a molecular basis for pathological strain diversity. Concurrently, the pathogenic focus has shifted toward nuclear loss of function, which triggers a systemic “RNA crisis” characterized by aberrant alternative polyadenylation (APA) and cryptic exon inclusion (e.g., STMN2, UNC13A). Crucially, this metabolic collapse is profoundly exacerbated by patient-specific genetic risk factors, acting synergistically in a “two-hit” model of neurodegeneration. To translate these findings to the clinic, next-generation diagnostic tools are emerging. Integrating neuron-derived extracellular vesicle (EV) isolation with Seed Amplification Assays (SAAs) holds promise to help overcome the structural camouflage that limits current PET imaging, potentially offering ultra-sensitive, functional strain identification in biofluids. While these structural and diagnostic milestones provide a strong foundation for precision medicine, major challenges in assay standardization and clinical validation must be addressed. Advanced therapeutic strategies—namely, splice-switching antisense oligonucleotides (ASOs) that directly restore RNA metabolism, combined with the targeted suppression of neuronal hyperexcitability—are now entering clinical trials. This review synthesizes how decoding the structural and RNA-metabolic complexities of TDP-43 is paving a promising pathway from bench to bedside, while critically discussing current translational limitations.
Findings support a dose-dependent SLC20A2 disease spectrum and expand the phenotype associated with biallelic loss of function from primary brain calcification toward severe early-onset neurodevelopmental disorder with prominent vascular and leptomeningeal calcification.
Mehmet Burak Mutlu, Abdullah Sezer, Elif Özdemir et al.· Journal of Human Genetics· 0 citations
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