Infantile-onset Ascending Hereditary Spastic Paralysis (IAHSP) is an ultrarare, autosomal recessive form of Hereditary Spastic Paraplegia (HSP), caused by mutations in the ALS2 gene, which encodes the protein ALSIN. In a previous study, we proposed a personalized therapeutic strategy for an Italian IAHSP patient (AO), aiming to correct the aberrant function of the R1611W mutant ALSIN using Menatetrenone (MK4). While our results supported compassionate-use approval for a patient-specific therapeutic regimen, further investigation was needed to highlight the treatment's benefits in the absence of tractable biophysical assays and in vivo models. In this respect, we first characterized MK4's interaction with the mutation site through Molecular Dynamics simulations. Next, we established and characterized a skin fibroblast cell line derived from patient AO. We analyzed the expression and stability of the mutant ALSIN protein in AO's fibroblasts and observed elevated oxidative stress levels. Using advanced microscopy and automated image analysis, we identified a characteristic mitochondrial phenotype associated with AO's IAHSP. One specific morphological parameter of mitochondria (Mean Branch Diameter) accurately reflected the IAHSP phenotype and was selected as a cell marker. Treatment of IAHSP fibroblasts with MK4 highlighted the rescue of Mean Branch Diameter and ALSIN levels, supporting cellular efficacy. Overall, this work presents an approach that integrates computational and cell-based methodologies to overcome the data scarcity challenges of drug discovery in rare diseases. Our study provides a framework for preclinical, alternative drug discovery programs in monogenic rare disorders such as IAHSP.

The Alsin Rho Guanine Nucleotide Exchange Factor (ALS2) gene encodes a protein alsin that functions as a guanine nucleotide exchange factor. The variations in ALS2 gene leads to degeneration of upper motor neurons of the corticospinal tract. The phenotypes resulting from variants in ALS2 gene are infantile-onset ascending hereditary spastic paralysis (IAHSP, OMIM # 607225), juvenile primary lateral sclerosis (JPLS, OMIM # 606353), and juvenile amyotrophic lateral sclerosis (JALS, OMIM # 205100). Our study objectives were to describe the clinical phenotype and genotype of children with an established diagnosis of ALS2 gene-related disorder. The clinical details, laboratory data, and genotype findings of children with an established diagnosis of ALS2 gene-related disorder were collected from the hospital electronic database after obtaining institutional review board approval. One family with three affected siblings, a second family with a proband and an affected fetus, and a third family with two affected siblings with ALS2 gene variants were identified. IAHSP was diagnosed in all of our patients with variants in ALS2 gene. The clinical findings observed in our patients were insidious onset progressive spastic paraparesis, contractures, and dysarthria. Nonsense variants were observed in four patients while frameshift variant was observed in one family. Novel variants in ALS2 gene were identified in two unrelated families. ALS2 mutation results in rare neurodegenerative disorders with the clinical spectrum encompassing IAHSP, JPLS, and JALS disorders. In view of allelic heterogeneity described in the literature, more research studies are needed for establishing genotype-phenotype correlation in patients with ALS2 gene-related disorder.

Infantile-onset ascending hereditary spastic paralysis (IAHSP), caused by bi-allelic variants in ALS2, is an ultra-rare, neurodegenerative disorder characterized by progressive ascending spasticity and weakness with bulbar dysfunction. To investigate baseline plasma neurofilament light chain (NfL) levels in children with IAHSP patients compared to age-matched controls. Five patients (age range: 6-11 years) with genetically confirmed IAHSP and 74 healthy controls were assessed. Plasma NfL was measured using a single-molecule array. Statistical analyses included non-parametric tests, age-matched comparisons, and effect size estimation. Children with IAHSP had modestly but significantly elevated plasma NfL levels compared to controls (median: 17.5 vs. 4.78 pg/mL, p = 0.004). High NfL levels persisted across varying levels of clinical severity. Plasma NfL levels are elevated in IAHSP, suggesting axonal degeneration. These pilot findings highlight NfL as a potential marker for disease activity, warranting further investigation in larger cohorts and longitudinal studies.

Despite the ubiquity of membrane occupation recognition nexus (MORN) motifs across diverse species in both eukaryotic and prokaryotic organisms, these protein domains remain poorly characterized. Their significance is underscored in the context of the Alsin protein, implicated in the debilitating condition known as infantile-onset ascending hereditary spastic paralysis (IAHSP). Recent investigations have proposed that mutations within the Alsin MORN domain disrupt proper protein assembly, precluding the formation of the requisite tetrameric configuration essential for the protein's inherent biological activity. However, a comprehensive understanding of the relationship between the biological functions of Alsin and its three-dimensional molecular structure is hindered by the lack of available experimental structures. In this study, we employed and compared several protein structure prediction algorithms to identify a three-dimensional structure for the putative MORN of Alsin. Furthermore, inspired by experimental pieces of evidence from previous studies, we employed the developed models to predict and investigate two homo-dimeric assemblies, characterizing their stability. This study's insights into the three-dimensional structure of the Alsin MORN domain and the stability dynamics of its homo-dimeric assemblies suggest an antiparallel linear configuration stabilized by a noncovalent interaction network.

ALS2-related disorder involves retrograde degeneration of the upper motor neurons of the pyramidal tracts, among which autosomal recessive Infantile-onset ascending hereditary spastic paralysis (IAHSP) is a rare phenotype. In this study, we gathered clinical data from two Chinese siblings who were affected by IAHSP. Our aim was to assess the potential pathogenicity of the identified variants and analyze their clinical and genetic characteristics. Here, Whole-exome sequencing (WES) was performed on proband to identify the candidate variants. Subsequently, Sanger sequencing was used to verify identified candidate variants and to assess co-segregation among available family members. Utilizing both silico prediction and 3D protein modeling, an analysis was conducted to evaluate the potential functional implications of the variants on the encoded protein, and minigene assays were performed to unravel the effect of the variants on the cleavage of pre-mRNA. Both patients were characterized by slurred speech, astasia, inability to walk, scoliosis, lower limb hypertonia, ankle clonus, contracture of joint, foot pronation and no psychomotor retardation was found. Genetic analysis revealed a novel homozygous variant of ALS2, c.1815G > T(p.Lys605Asn) in two Chinese siblings. To our knowledge, it is the first confirmed case of a likely pathogenic variant leading to IAHSP in a Chinese patient. This study broadens the range of ALS2 variants and has practical implications for prenatal and postnatal screening of IAHSR. Symptom-based diagnosis of IAHSP is frequently difficult for medical practitioners. WES can be a beneficial resource to identify a particular disorder when the diagnosis cannot be determined from the symptoms alone.