Efficacy of AAV9-mediated SGPL1 gene transfer in a mouse model of S1P lyase insufficiency syndrome

Phenotypic quantification of Nphs1-deficient mice

BACKGROUND

Steroid-resistant nephrotic syndrome (SRNS) is the second most frequent cause of chronic kidney disease in children and young adults. The most severe form of steroid-resistant nephrotic syndrome is congenital nephrotic syndrome Finnish type (CNSF), caused by biallelic loss-of-function variants in NPHS1, encoding nephrin. Since each of the 68 monogenic causes of steroid-resistant nephrotic syndrome represents a rare cause of the disease, tailoring therapeutic interventions to multiple molecular targets remains challenging, suggesting gene replacement therapy (GRT) as a viable alternative. To set the ground for a gene replacement study in vivo, we established rigorous, quantifiable, and reproducible phenotypic assessment of a conditional Nphs1 knockout mouse model.

METHODS

By breeding a floxed Nphs1fl/- mouse (Nphs1tm1Afrn/J) previously studied for pancreatic β-cell survival with a podocin promoter-driven Cre recombinase mouse model (Tg(NPHS2-Cre)295Lbh/J), we generated mice with podocyte-specific nephrin deficiency (Nphs1fl/fl NPHS2-Cre +).

RESULTS

We observed a median survival to postnatal day P5 in nephrin-deficient mice, whereas heterozygous control mice and wild type (WT) control group showed 90% and 100% survival, respectively (at P50 days). Light microscopy analysis showed a significantly higher number of renal-tubular microcysts per kidney section in nephrin-deficient mice compared to the control groups (P < 0.0022). Transmission electron microscopy demonstrated reduced foot process (FP) density in nephrin-deficient mice compared to controls (P < 0.0001). Additionally, proteinuria quantitation using urine albumin-to-creatinine ratio (UACR) was significantly higher in nephrin-deficient mice compared to controls.

CONCLUSIONS

This study represents the first comprehensive description of the kidney phenotype in a nephrin-deficient mouse model, laying the foundation for future gene replacement therapy endeavors.

Quantifiable and reproducible phenotypic assessment of a constitutive knockout mouse model for congenital nephrotic syndrome of the Finnish type

Steroid-resistant nephrotic syndrome (SRNS) is the second most frequent cause of childhood chronic kidney disease. Congenital nephrotic syndrome of the Finnish type (CNF) (MIM# 256300) is caused by biallelic variants in the gene NPHS1, encoding nephrin, an integral component of the kidney filtration barrier. No causal treatments exist, and children inevitably require kidney replacement therapy. In preparation for gene replacement therapy (GRT) in CNF, we established a quantifiable and reproducible phenotypic assessment of the nephrin-deficient CNF mouse model: 129/Sv-Nphs1tm1Rkl/J. We assessed the phenotypic spectrum of homozygous mice (Nphs1tm1Rkl/Nphs1tm1Rkl) compared to heterozygous controls (Nphs1tm1Rkl/Nphs1WT) by the following parameters: 1. cohort survival, 2. podocyte foot process (FP) density per glomerular basement membrane (GBM) using transmission electron microscopy, 3. tubular microcysts in brightfield microscopy, and 4. urinary albumin/creatinine ratios. Nphs1tm1Rkl/Nphs1tm1Rkl mice exhibited: 1. perinatal lethality with median survival of 1 day, 2. FP effacement with median FP density of 1.00 FP/µm GBM (2.12 FP/µm in controls), 3. tubular dilation with 65 microcysts per section (6.5 in controls), and 4. increased albumin/creatinine ratio of 238 g/g (4.1 g/g in controls). We here established four quantifiable phenotyping features of a CNF mouse model to facilitate future GRT studies by enabling sensitive detection of phenotypic improvements.

BDNF Modulation by microRNAs: An Update on the Experimental Evidence

MicroRNAs can interfere with protein function by suppressing their messenger RNA translation or the synthesis of its related factors. The function of brain-derived neurotrophic factor (BDNF) is essential to the proper formation and function of the nervous system and is seen to be regulated by many microRNAs. However, understanding how microRNAs influence BDNF actions within cells requires a wider comprehension of their integrative regulatory mechanisms. Aim: In this literature review, we have synthesized the evidence of microRNA regulation on BDNF in cells and tissues, and provided an analytical discussion about direct and indirect mechanisms that appeared to be involved in BDNF regulation by microRNAs. Methods: Searches were conducted on PubMed.gov using the terms "BDNF" AND "MicroRNA" and "brain-derived neurotrophic factor" AND "MicroRNA", updated on 1 September 2023. Papers without open access were requested from the authors. One hundred and seventy-one papers were included for review and discussion. Results and Discussion: The local regulation of BDNF by microRNAs involves a complex interaction between a series of microRNAs with target proteins that can either inhibit or enhance BDNF expression, at the core of cell metabolism. Therefore, understanding this homeostatic balance provides resources for the future development of vector-delivery-based therapies for the neuroprotective effects of BDNF.

Gene therapy with AAV9-SGPL1 in an animal model of lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive scarring disease of the lung that leads rapidly to respiratory failure. Novel approaches to treatment are urgently needed. The bioactive lipid sphingosine-1-phosphate (S1P) is increased in IPF lungs and promotes proinflammatory and profibrotic TGF-β signaling. Hence, decreasing lung S1P represents a potential therapeutic strategy for IPF. S1P is degraded by the intracellular enzyme S1P lyase (SPL). Here we find that a knock-in mouse with a missense SPL mutation mimicking human disease resulted in reduced SPL activity, increased S1P, increased TGF-β signaling, increased lung fibrosis, and higher mortality after injury compared to wild type (WT). We then tested adeno-associated virus 9 (AAV9)-mediated overexpression of human SGPL1 (AAV-SPL) in mice as a therapeutic modality. Intravenous treatment with AAV-SPL augmented lung SPL activity, attenuated S1P levels within the lungs, and decreased injury-induced fibrosis compared to controls treated with saline or only AAV. We confirmed that AAV-SPL treatment led to higher expression of SPL in the epithelial and fibroblast compartments during bleomycin-induced lung injury. Additionally, AAV-SPL decreased expression of the profibrotic cytokines TNFα and IL1β as well as markers of fibroblast activation, such as fibronectin (Fn1), Tgfb1, Acta2, and collagen genes in the lung. Taken together, our results provide proof of concept for the use of AAV-SPL as a therapeutic strategy for the treatment of IPF. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Current Status and Prospects of Viral Vector-Based Gene Therapy to Treat Kidney Diseases

Inherited kidney diseases are among the leading causes of chronic kidney disease, reducing the quality of life and resulting in substantial socioeconomic impact. The advent of early genetic testing and the growing understanding of the molecular basis and pathophysiology of these disorders have opened avenues for novel treatment strategies. Viral vector-based gene therapies have evolved from experimental treatments for rare diseases to potent platforms that carry the intrinsic potential to provide a cure with a single application. Several gene therapy products have reached the market, and the numbers are only expected to increase. Still, none target inherited kidney diseases. Gene transfer to the kidney has lagged when compared to other tissue-directed therapies such as hepatic, neuromuscular, and ocular tissues. Systemic delivery of genetic information to tackle kidney disease is challenging. The pharma industry is taking steps to take on kidney disease and to translate the current research into the therapeutic arena. In this review, we provide an overview of the current viral vector-based approaches and their potential. We discuss advances in platforms and injection routes that have been explored to enhance gene delivery toward kidney cells in animal models, and how these can fuel the development of viable gene therapy products for humans.

AAV-SPL 2.0, a Modified Adeno-Associated Virus Gene Therapy Agent for the Treatment of Sphingosine Phosphate Lyase Insufficiency Syndrome

Sphingosine-1-phosphate lyase insufficiency syndrome (SPLIS) is an inborn error of metabolism caused by inactivating mutations in SGPL1, the gene encoding sphingosine-1-phosphate lyase (SPL), an essential enzyme needed to degrade sphingolipids. SPLIS features include glomerulosclerosis, adrenal insufficiency, neurological defects, ichthyosis, and immune deficiency. Currently, there is no cure for SPLIS, and severely affected patients often die in the first years of life. We reported that adeno-associated virus (AAV) 9-mediated SGPL1 gene therapy (AAV-SPL) given to newborn Sgpl1 knockout mice that model SPLIS and die in the first few weeks of life prolonged their survival to 4.5 months and prevented or delayed the onset of SPLIS phenotypes. In this study, we tested the efficacy of a modified AAV-SPL, which we call AAV-SPL 2.0, in which the original cytomegalovirus (CMV) promoter driving the transgene is replaced with the synthetic "CAG" promoter used in several clinically approved gene therapy agents. AAV-SPL 2.0 infection of human embryonic kidney (HEK) cells led to 30% higher SPL expression and enzyme activity compared to AAV-SPL. Newborn Sgpl1 knockout mice receiving AAV-SPL 2.0 survived ≥ 5 months and showed normal neurodevelopment, 85% of normal weight gain over the first four months, and delayed onset of proteinuria. Over time, treated mice developed nephrosis and glomerulosclerosis, which likely resulted in their demise. Our overall findings show that AAV-SPL 2.0 performs equal to or better than AAV-SPL. However, improved kidney targeting may be necessary to achieve maximally optimized gene therapy as a potentially lifesaving SPLIS treatment.

Recent Advances in Proteinuric Kidney Disease/Nephrotic Syndrome: Lessons from Knockout/Transgenic Mouse Models

Proteinuria is known to be associated with all-cause and cardiovascular mortality, and nephrotic syndrome is defined by the level of proteinuria and hypoalbuminemia. With advances in medicine, new causative genes for genetic kidney diseases are being discovered increasingly frequently. We reviewed articles on proteinuria/nephrotic syndrome, focal segmental glomerulosclerosis, membranous nephropathy, diabetic kidney disease/nephropathy, hypertension/nephrosclerosis, Alport syndrome, and rare diseases, which have been studied in mouse models. Significant progress has been made in understanding the genetics and pathophysiology of kidney diseases thanks to advances in science, but research in this area is ongoing. In the future, genetic analyses of patients with proteinuric kidney disease/nephrotic syndrome may ultimately lead to personalized treatment options.

Sphingosine phosphate lyase insufficiency syndrome: a systematic review

BACKGROUND

Sphingosine-1-phosphate lyase insufficiency syndrome (SPLIS) or nephrotic syndrome type-14 is caused by biallelic mutations in SGPL1. Here, we conducted a systematic review to delineate the characteristics of SPLIS patients.

METHODS

A literature search was performed in PubMed, Web of Science, and Scopus databases, and eligible studies were included. For all patients, demographic, clinical, laboratory, and molecular data were collected and analyzed.

RESULTS

Fifty-five SPLIS patients (54.9% male, 45.1% female) were identified in 19 articles. Parental consanguinity and positive family history were reported in 70.9% and 52.7% of patients, respectively. Most patients (54.9%) primarily manifested within the first year of life, nearly half of whom survived, while all patients with a prenatal diagnosis of SPLIS (27.5%) died at a median [interquartile (IQR)] age of 2 (1.4-5.3) months (P = 0.003). The most prevalent clinical feature was endocrinopathies, including primary adrenal insufficiency (PAI) (71.2%) and hypothyroidism (32.7%). Kidney disorders (42, 80.8%) were mainly in the form of steroid-resistant nephrotic syndrome (SRNS) and progressed to end-stage kidney disease (ESKD) in 19 (36.5%) patients at a median (IQR) age of 6 (1.4-42.6) months. Among 30 different mutations in SGPL1, the most common was c.665G > A (p.Arg222Gln) in 11 (20%) patients. Twenty-six (49.1%) patients with available outcome were deceased at a median (IQR) age of 5 (1.5-30.5) months, mostly following ESKD (23%) or sepsis/septic shock (23%).

CONCLUSION

In patients with PAI and/or SRNS, SGPL1 should be added to diagnostic genetic panels, which can provide an earlier diagnosis of SPLIS and prevention of ESKD and other life-threatening complications.

A rare cause of nephrotic syndrome-sphingosine-1-phosphate lyase (SGPL1) deficiency: 6 cases and a review of the literature

BACKGROUND

Recently, recessive mutations in SGPL1 (sphingosine-1-phosphate lyase), which encodes the final enzyme of sphingolipid metabolism, have been reported to cause steroid-resistant nephrotic syndrome, adrenal insufficiency, and many other organ/system involvements. We aimed to determine the clinical and genetic characteristics, and outcomes in patients with SGPL1 mutations.

METHODS

The study included 6 patients with bi-allelic SGPL1 mutation. Clinical, genetic, and laboratory characteristics, and outcomes of the patients were evaluated retrospectively. We also reviewed previously reported patients with SGPL1 mutations and compared them to the presented patients.

RESULTS

The median age at kidney presentation was 5 months. Four patients (67%) were diagnosed before age 1 year. Kidney biopsy showed focal segmental glomerulosclerosis in 2 patients and diffuse mesangial sclerosis in one patient. Steroids were given to 3 patients, but they did not respond. All 6 patients progressed to chronic kidney disease; 5 required kidney replacement therapy (KRT) at a median age of 6 months. Deceased kidney transplantation was performed in one patient. All 6 patients had adrenal insufficiency, of which 5 were diagnosed at age < 6 months. Three patients had hypothyroidism, 2 had ichthyosis, 4 had immunodeficiency, 5 had neurological findings, and 2 had genitourinary system anomalies. Four patients died at a median age of 30.5 months. Two patients are being followed up with KRT. One patient had a novel mutation.

CONCLUSIONS

Patients with SGPL1 mutations have a poor prognosis, and many types of extrarenal organ/system involvement beyond adrenal insufficiency can be seen. Genetic diagnosis of such patients is important for treatment, genetic counseling, and screening for comorbid conditions. A higher resolution version of the Graphical abstract is available as Supplementary information.

Neurological Consequences of Sphingosine Phosphate Lyase Insufficiency

In 2017, an inborn error of metabolism caused by recessive mutations in SGPL1 was discovered. The disease features steroid-resistant nephrotic syndrome, adrenal insufficiency, and neurological defects. The latter can include sensorineural hearing loss, cranial nerve defects, peripheral neuropathy, abnormal brain development, seizures and/or neurodegeneration. SGPL1 encodes the pyridoxal-5’-phosphate (PLP) dependent enzyme sphingosine phosphate lyase (SPL), and the condition is now referred to as SPL insufficiency syndrome (SPLIS). SPL catalyzes the final step in the degradative pathway of sphingolipids in which the bioactive sphingolipid sphingosine-1-phosphate (S1P) is irreversibly degraded to a long chain aldehyde and phosphoethanolamine (PE). SPL guards the only exit point for sphingolipid metabolism, and its inactivation leads to accumulation of various types of sphingolipids which have biophysical roles in plasma membrane rafts and myelin, and signaling roles in cell cycle progression, vesicular trafficking, cell migration, and programmed cell death. In addition, the products of the SPL reaction have biological functions including regulation of autophagic flux, which is important in axonal and neuronal integrity. In this review, the neurological manifestations of SPLIS will be described, and insights regarding the neurological consequences of SPL insufficiency from the study of brain-specific SPL knockout mice and Drosophila SPL mutants will be summarized.

Integrating basic science with translational research: the 13th International Podocyte Conference 2021

The 13th International Podocyte Conference was held in Manchester, UK, and online from July 28 to 30, 2021. Originally planned for 2020, this biannual meeting was postponed by a year because of the coronavirus disease 2019 (COVID-19) pandemic and proceeded as an innovative hybrid meeting. In addition to in-person attendance, online registration was offered, and this attracted 490 conference registrations in total. As a Podocyte Conference first, a day for early-career researchers was introduced. This premeeting included talks from graduate students and postdoctoral researchers. It gave early career researchers the opportunity to ask a panel, comprising academic leaders and journal editors, about career pathways and the future for podocyte research. The main meeting over 3 days included a keynote talk and 4 focused sessions each day incorporating invited talks, followed by selected abstract presentations, and an open panel discussion. The conference concluded with a Patient Day, which brought together patients, clinicians, researchers, and industry representatives. The Patient Day was an interactive and diverse day. As well as updates on improving diagnosis and potential new therapies, the Patient Day included a PodoArt competition, exercise and cooking classes with practical nutrition advice, and inspirational stories from patients and family members. This review summarizes the exciting science presented during the 13th International Podocyte Conference and demonstrates the resilience of researchers during a global pandemic.

Sphingosine Phosphate Lyase Is Upregulated in Duchenne Muscular Dystrophy, and Its Inhibition Early in Life Attenuates Inflammation and Dystrophy in Mdx Mice

Duchenne muscular dystrophy (DMD) is a congenital myopathy caused by mutations in the dystrophin gene. DMD pathology is marked by myositis, muscle fiber degeneration, and eventual muscle replacement by fibrosis and adipose tissue. Satellite cells (SC) are muscle stem cells critical for muscle regeneration. Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that promotes SC proliferation, regulates lymphocyte trafficking, and is irreversibly degraded by sphingosine phosphate lyase (SPL). Here, we show that SPL is virtually absent in normal human and murine skeletal muscle but highly expressed in inflammatory infiltrates and degenerating fibers of dystrophic DMD muscle. In mdx mice that model DMD, high SPL expression is correlated with dysregulated S1P metabolism. Perinatal delivery of the SPL inhibitor LX2931 to mdx mice augmented muscle S1P and SC numbers, reduced leukocytes in peripheral blood and skeletal muscle, and attenuated muscle inflammation and degeneration. The effect on SC was also observed in SCID/mdx mice that lack mature T and B lymphocytes. Transcriptional profiling in the skeletal muscles of LX2931-treated vs. control mdx mice demonstrated changes in innate and adaptive immune functions, plasma membrane interactions with the extracellular matrix (ECM), and axon guidance, a known function of SC. Our cumulative findings suggest that by raising muscle S1P and simultaneously disrupting the chemotactic gradient required for lymphocyte egress, SPL inhibition exerts a combination of muscle-intrinsic and systemic effects that are beneficial in the context of muscular dystrophy.

Building cross-border collaborations to increase diversity and accelerate rare disease drug development - meeting report from the inaugural IndoUSrare Annual Conference 2021

The inaugural IndoUSrare Annual Conference was held virtually from 29 November to 2 December 2021 and was organized by the Indo US Organization for Rare Diseases (IndoUSrare). The event saw participation from over 250 stakeholders of rare diseases who joined in virtually by audio/video on the Zoom platform from around the world, with a majority of attendees concentrated in the Indian subcontinent and the United States. The conference was held over 4 days from 10:00 a.m. to 12:30 p.m. Eastern Time on each day, which accommodated participation by speakers and attendees from both the eastern and western hemispheres. The agenda over 4 days holistically covered broad topics of interest to different stakeholder groups such as representatives from organizations working toward policy frameworks for rare diseases or orphan drugs (Days 1, 4), biomedical research institutions (Day 2), patient advocacy organizations (Day 3), and patient advocacy and engagement offices within Industry (Day 4). In this meeting report, we summarize the key highlights from each day of this conference, with a perspective on future directions encouraging cross-border multistakeholder collaborations to maximize diversity, equity, and inclusion (DEI) in rare disease diagnosis, research, clinical trials, and treatment access. Each day included a keynote lecture on the theme of the day followed by a series of individual speaker presentations and/or a panel discussion. The goal was to understand current barriers and bottlenecks in the rare disease ecosystem. The discussions also helped highlight gaps and identify potential solutions that can be achieved through building multistakeholder collaborations across international borders, which we believe IndoUSrare is uniquely positioned to do with organizational programs such as rare patient foundation alliance, technology-enabled patient concierge, research corps, and corporate alliance program. The inaugural conference of the then 2+-year-old IndoUSrare organization laid the foundation for ongoing engagement of stakeholders between the two countries - the United States and India. The long-term goal is to scale the conference more broadly and serve as a model for other low- and middle-income countries (LMICs).

Plain language summary

IndoUSrare held its inaugural Annual Conference from 29 November to 2 December 2021. It was focused on the theme of cross-border collaborations for rare disease drug development, with each day dedicated to a specific patient-focused discussion topic, ranging from patient-led advocacy (Advocacy Day), research (Research Day), rare disease community support and engagement (Patients Alliance Day), to industry collaborations (Industry Day). The 4-day conference was held in virtual mode and attracted over 250 attendees from across the globe. This meeting report provides the key highlights of the event and summarizes learnings and future directions encouraging cross-border collaborations to increase diversity, equity, and inclusion (DEI) in rare disease research and clinical trials.

Advances in mouse genetics for the study of human disease

The mouse is the pre-eminent model organism for studies of mammalian gene function and has provided an extraordinarily rich range of insights into basic genetic mechanisms and biological systems. Over several decades, the characterization of mouse mutants has illuminated the relationship between gene and phenotype, providing transformational insights into the genetic bases of disease. However, if we are to deliver the promise of genomic and precision medicine, we must develop a comprehensive catalogue of mammalian gene function that uncovers the dark genome and elucidates pleiotropy. Advances in large-scale mouse mutagenesis programmes allied to high-throughput mouse phenomics are now addressing this challenge and systematically revealing novel gene function and multi-morbidities. Alongside the development of these pan-genomic mutational resources, mouse genetics is employing a range of diversity resources to delineate gene-gene and gene-environment interactions and to explore genetic context. Critically, mouse genetics is a powerful tool for assessing the functional impact of human genetic variation and determining the causal relationship between variant and disease. Together these approaches provide unique opportunities to dissect in vivo mechanisms and systems to understand pathophysiology and disease. Moreover, the provision and utility of mouse models of disease has flourished and engages cumulatively at numerous points across the translational spectrum from basic mechanistic studies to pre-clinical studies, target discovery and therapeutic development.

Mouse Liver Compensates Loss of Sgpl1 by Secretion of Sphingolipids into Blood and Bile

Sphingosine 1 phosphate (S1P) lyase (Sgpl1) catalyses the irreversible cleavage of S1P and thereby the last step of sphingolipid degradation. Loss of Sgpl1 in humans and mice leads to accumulation of sphingolipids and multiple organ injuries. Here, we addressed the role of hepatocyte Sgpl1 for regulation of sphingolipid homoeostasis by generating mice with hepatocyte-specific deletion of Sgpl1 (Sgpl1HepKO mice). Sgpl1HepKO mice had normal body weight, liver weight, liver structure and liver enzymes both at the age of 8 weeks and 8 months. S1P, sphingosine and ceramides, but not glucosylceramides or sphingomyelin, were elevated by ~1.5-2-fold in liver, and this phenotype did not progress with age. Several ceramides were elevated in plasma, while plasma S1P was normal. Interestingly, S1P and glucosylceramides, but not ceramides, were elevated in bile of Sgpl1HepKO mice. Furthermore, liver cholesterol was elevated, while LDL cholesterol decreased in 8-month-old mice. In agreement, the LDL receptor was upregulated, suggesting enhanced uptake of LDL cholesterol. Expression of peroxisome proliferator-activated receptor-γ, liver X receptor and fatty acid synthase was unaltered. These data show that mouse hepatocytes largely compensate the loss of Sgpl1 by secretion of accumulating sphingolipids in a specific manner into blood and bile, so that they can be excreted or degraded elsewhere.

Outcomes of progranulin gene therapy in the retina are dependent on time and route of delivery

Neuronal ceroid lipofuscinosis (NCL) is a family of neurodegenerative diseases caused by mutations to genes related to lysosomal function. One variant, CNL11, is caused by mutations to the gene encoding the protein progranulin, which regulates neuronal lysosomal function. Absence of progranulin causes cerebellar atrophy, seizures, dementia, and vision loss. As progranulin gene therapies targeting the brain are developed, it is advantageous to focus on the retina, as its characteristics are beneficial for gene therapy development: the retina is easily visible through direct imaging, can be assessed through quantitative methods in vivo, and requires smaller amounts of adeno-associated virus (AAV). In this study we characterize the retinal degeneration in a progranulin knockout mouse model of CLN11 and study the effects of gene replacement at different time points. Mice heterologously expressing progranulin showed a reduction in lipofuscin deposits and microglia infiltration. While mice that receive systemic AAV92YF-scCAG-PGRN at post-natal day 3 or 4 show a reduction in retina thinning, mice injected intravitreally at months 1 and 6 with AAV2.7m8-scCAG-PGRN exhibit no improvement, and mice injected at 12 months of age have thinner retinas than do their controls. Thus, delivery of progranulin proves to be time sensitive and dependent on route of administration, requiring early delivery for optimal therapeutic benefit.

Genotype/Phenotype Interactions and First Steps Toward Targeted Therapy for Sphingosine Phosphate Lyase Insufficiency Syndrome

Sphingosine-1-phosphate lyase insufficiency syndrome (SPLIS) is a rare metabolic disorder caused by a deficiency in sphingosine-1-phosphate lyase (SPL), the final enzyme in the sphingolipid degradative pathway. Inactivating mutations of SGPL1-the gene encoding SPL-lead to a deficiency of its downstream products, and buildup of sphingolipid intermediates, including its bioactive substrate, sphingosine-1-phosphate (S1P), the latter causing lymphopenia, a hallmark of the disease. Other manifestations of SPLIS include nephrotic syndrome, neuronal defects, and adrenal insufficiency, but their pathogenesis remains unknown. In this report, we describe the correlation between SGPL1 genotypes, age at diagnosis, and patient outcome. Vitamin B6 serves as a cofactor for SPL. B6 supplementation may aid some SPLIS patients by overcoming poor binding kinetics and promoting proper folding and stability of mutant SPL proteins. However, this approach remains limited to patients with a susceptible allele. Gene therapy represents a potential targeted therapy for SPLIS patients harboring B6-unresponsive missense mutations, truncations, deletions, and splice-site mutations. When Sgpl1 knockout (SPLKO) mice that model SPLIS were treated with adeno-associated virus (AAV)-mediated SGPL1 gene therapy, they showed profound improvement in survival and kidney and neurological function compared to untreated SPLKO mice. Thus, gene therapy appears promising as a universal, potentially curative treatment for SPLIS.