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.

Spinal muscular atrophy is a rare and progressive neuromuscular disease that, without treatment, leads to progressive weakness and often death. A plethora of studies have led to the approval of three high-cost and effective treatments since 2016. These treatments, nusinersen, onasemnogene abeparvovec, and risdiplam, have not been directly compared and have varying challenges in administration. In this review, we discuss the evidence supporting the use of these medications, the process of treatment selection, monitoring after treatment, the limited data comparing treatments, as well as future directions for investigation and therapy.

Throughout the years, several hundred million people with rare genetic disorders have been receiving only symptom management therapy. However, research and development efforts worldwide have led to the development of long-lasting, highly efficient, and safe gene therapy for a wide range of hereditary diseases. Improved viral vectors are now able to evade the preexisting immunity and more efficiently target and transduce therapeutically relevant cells, ensuring genome maintenance and expression of transgenes at the relevant levels. Hematological, ophthalmological, neurodegenerative, and metabolic therapeutic areas have witnessed successful treatment of hemophilia and muscular dystrophy, restoration of immune system in children with immunodeficiencies, and restoration of vision. This review focuses on three leading vector platforms of the past two decades: adeno-associated viruses (AAVs), adenoviruses (AdVs), and lentiviruses (LVs). Special attention is given to successful preclinical and clinical studies that have led to the approval of gene therapies: six AAV-based (Glybera® for lipoprotein lipase deficiency, Luxturna® for retinal dystrophy, Zolgensma® for spinal muscular atrophy, Upstaza® for AADC, Roctavian® for hemophilia A, and Hemgenix® for hemophilia B) and three LV-based (Libmeldy® for infantile metachromatic leukodystrophy, Zynteglo® for β-thalassemia, and Skysona® for ALD). The review also discusses the problems that arise in the development of gene therapy treatments, which, nevertheless, do not overshadow the successes of already developed gene therapies and the hope these treatments give to long-suffering patients and their families.

UNASSIGNED: Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by mutations in the survival motor neuron 1 (SMN1) gene. In clinical studies, gene replacement therapy with onasemnogene abeparvovec (formerly AVXS-101, Zolgensma®, Novartis) was efficacious in improving motor functioning in children with SMA. However, its effects on cognitive and language skills are largely unknown.
UNASSIGNED: This longitudinal observational study evaluated changes in motor and neurocognitive functioning over a 1-year period after administration of onasemnogene abeparvovec in 12 symptomatic SMA type 1 patients with two copies of SMN2 aged 1.7-52.6 months at administration. Motor functioning was measured using the Children\'s Hospital of Philadelphia Infant Test for Neuromuscular Disorders (CHOP-INTEND) while neurocognitive assessment was measured using Griffiths III. Motor milestones and language ability were also assessed at each timepoint.
UNASSIGNED: Statistically significant increases in median CHOP-INTEND scores from baseline were observed at 1, 3, 6, and 12 months after onasemnogene abeparvovec administration (all p ≤ 0.005). Most (91.7%) patients were able to roll over or sit independently for >1 min at 12 months. Significant increases in the Griffiths III Foundations of Learning, Language and Communication, Eye and Hand Coordination, and Personal-Social-Emotional subscale scores were observed at 12-months, but not in the Gross Motor subscale. Speech and language abilities progressed in most patients. Overall, most patients showed some improvement in cognitive and communication performance after treatment with onasemnogene abeparvovec in addition to significant improvement in motor functioning and motor milestones. Evaluation of neurocognitive function should be considered when assessing the global functioning of patients with SMA.

Leber congenital amaurosis (LCA) is the most common genetic cause of congenital visual impairment in infants and children. Patients with LCA who harbor RPE65 mutations exhibit a deficiency in photoreceptor rhodopsin, leading to severe night blindness and visual impairment following birth. Since either gene replacement therapy or anti-apoptosis therapy alone cannot maintain both functional and morphological normality for a long time in the animal model, we propose a robust treatment strategy, that is, gene replacement therapy combined with anti-apoptotic therapy to protect photoreceptors from further degeneration while compensating for lost RPE65 function. Here, rd12 mice were injected subretinally at postnatal day 14 with four vector administrations, respectively. At 6 months after treatment, it was discovered that injection of three vectors, AAV8 (Y733F)-CBA-hRPE65, AAV8(Y733F)-CBA-hRPE65-BCL-2-L10 and mixture of half-dose AAV8(Y733F)-CBA-hRPE65 and half-dose AAV8 (Y733F)-CBA-BCL-2-L10, could partially restore the visual function of rd12 mice. Meanwhile, these treated eyes also exhibited a thicker outer nuclear layer (ONL) structure. However, despite the fact that the eyes of rd12 mice injected with the AAV8 (Y733F)-CBA-BCL-2-L10 vector displayed a slightly thicker ONL structure compared to untreated eyes, the visual function of the treated eyes did not recover. Continuing the observation period to 12 months after treatment, we found that compared to rd12 mice at 6-month post-treatment, rd12 mice injected with AAV8 (Y733F)-CBA-hRPE65 or mixture of half-dose AAV8(Y733F)-CBA-hRPE65 and half-dose AAV8 (Y733F)-CBA-BCL-2-L10 exhibited varying degrees of decline in both visual function and ONL thickness. However, in the case of rd12 mice injected with the AAV8(Y733F)-CBA-hRPE65-BCL-2-L10 vector, the ONL thickness remains consistent at both 6 and 12 months after treatment. These mice continued to maintain a relatively strong visual function and showed restoration in the levels of RPE65 and Rhodopsin protein expression. Our findings illustrate that early postnatal treatment with AAV vectors containing both the hRPE65 gene and the Bcl-2L10 anti-apoptotic gene provide enhanced and sustained retinal protection.

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder that causes muscle atrophy and weakness. While no specific therapies existed until a few years ago, several effective disease-modifying treatments have become available in recent years. However, there are currently no recommendations on the management of therapy sequencing involving these new treatments. A 4-months-old girl with SMA type 1 and two copies of SMN2 was started on treatment with nusinersen resulting in significant improvement in her motor and respiratory function. However, after six doses, treatment was changed to Zolgensma® due to caregiver\'s decision. In the months following the administration, the patient showed significant clinical improvement in motor performance. After 12 months, the child started therapy with risdiplam in another country. One year after the start of therapy with risdiplam further improvements in both motor and bulbar functions were highlighted. This case report raises a question: is a multiple consecutive theraphy more effective than monotherapy in SMA treatment? These results suggest the need to further explore the potential efficacy of a multidrug treatment.

BACKGROUND: X-linked myotubular myopathy (XLMTM) is a rare, life-threatening congenital muscle disease caused by mutations in the MTM1 gene that result in profound muscle weakness, significant respiratory insufficiency, and high infant mortality. There is no approved disease-modifying therapy for XLMTM. Resamirigene bilparvovec (AT132; rAAV8-Des-hMTM1) is an investigational adeno-associated virus (AAV8)-mediated gene replacement therapy designed to deliver MTM1 to skeletal muscle cells and achieve long-term correction of XLMTM-related muscle pathology. The clinical trial ASPIRO (NCT03199469) investigating resamirigene bilparvovec in XLMTM is currently paused while the risk:benefit balance associated with this gene therapy is further investigated.
METHODS: Muscle biopsies were taken before treatment and 24 and 48 weeks after treatment from ten boys with XLMTM in a clinical trial of resamirigene bilparvovec (ASPIRO; NCT03199469). Comprehensive histopathological analysis was performed.
RESULTS: Baseline biopsies uniformly showed findings characteristic of XLMTM, including small myofibres, increased internal or central nucleation, and central aggregates of organelles. Biopsies taken at 24 weeks post-treatment showed marked improvement of organelle localisation, without apparent increases in myofibre size in most participants. Biopsies taken at 48 weeks, however, did show statistically significant increases in myofibre size in all nine biopsies evaluated at this timepoint. Histopathological endpoints that did not demonstrate statistically significant changes with treatment included the degree of internal/central nucleation, numbers of triad structures, fibre type distributions, and numbers of satellite cells. Limited (predominantly mild) treatment-associated inflammatory changes were seen in biopsy specimens from five participants.
CONCLUSIONS: Muscle biopsies from individuals with XLMTM treated with resamirigene bilparvovec display statistically significant improvement in organelle localisation and myofibre size during a period of substantial improvements in muscle strength and respiratory function. This study identifies valuable histological endpoints for tracking treatment-related gains with resamirigene bilparvovec, as well as endpoints that did not show strong correlation with clinical improvement in this human study.
BACKGROUND: Astellas Gene Therapies (formerly Audentes Therapeutics, Inc.).

UNASSIGNED: Spinal muscular atrophy (SMA) is a genetic neurodegenerative disease leading to muscular weakness and premature death. Three therapeutic options are currently available including gene replacement therapy (GRT), which is potentially cardiotoxic. High-sensitive cardiac troponin I (hs-cTnI) is widely used to monitor potential cardiac contraindications or side effects of GRT, but reference data in healthy newborns are limited and lacking in neonates with SMA. The aim of this study is to determine the range of pre-therapeutic hs-cTnI concentrations in neonates with SMA and to provide guidance for the assessment of these values.
UNASSIGNED: Hs-cTnI levels, genetic and clinical data of 30 newborns (age range 2-26 days) with SMA were retrospectively collected from 6 German neuromuscular centers. In addition, hs-cTnI levels were measured in 16 neonates without SMA.
UNASSIGNED: The median hs-cTnI concentration in neonates with SMA was 39.5 ng/L (range: 4-1205). In 16 newborns with SMA, hs-cTnI levels were above the test-specific upper reference limit (URL). Exploratory statistical analysis revealed no relevant correlation between hs-cTnI levels and gender, gestational age, mode of delivery, SMN2 copy number, symptoms of SMA or abnormal cardiac findings.
UNASSIGNED: Our results suggest higher hs-cTnI plasma levels in newborns with and without SMA compared to assay-specific reference values generated in adults. Given the wide range of hs-cTnI values in neonates with SMA, hs-cTnI levels must be determined before treatment in each patient and post-treatment elevations should be interpreted in the context of the course rather than as individual values.

Onasemnogene abeparvovec (OA) is the only gene replacement therapy currently approved for spinal muscular atrophy (SMA) treatment. We sought to assess real-world patient and caregiver outcomes after OA treatment for SMA.
Patients who received OA were identified from the 2021 Cure SMA Membership Survey. Those treated at 6-23 months of age were matched to non-patients treated with OA on the basis of age at the time of survey and survival motor neuron 2 gene copy number. Patient characteristics, motor milestones, and resource and supportive care use, as well as caregiver proxy-reported health-related quality of life (HRQOL), were described. Caregiver unmet needs and HRQOL were also assessed.
Of the 614 patients in the survey, 64 received OA, and 17 were matched with 28 non-OA-treated patients. In general, a greater percentage of OA-treated patients achieved various motor milestones, including 100% sitting without support and 58.8% walking with assistance. OA-treated patients also had numerically lower rates of hospitalization and surgery. None required tracheostomy with a ventilator. The rate of using oxygen or a breathing machine for more than 16 h was also lower for OA-treated patients. OA-treated patients had less frequent trouble swallowing. HRQOL was reported to be similar to non-OA-treated patients. Caregivers of OA-treated patients reported better patient mobility scores and less work impairment.
The study suggests that treatment with OA is associated with greater rates of motor milestone achievements and less resource and supportive care use for patients with SMA treated at 6-23 months of age in the real world. For caregivers, it may also potentially reduce unmet needs, improve HRQOL, and reduce work impairment.

The introduction and development of biologics such as therapeutic proteins, gene-, and cell-based therapy have revolutionized the scope of treatment for many diseases. However, a significant portion of the patients develop unwanted immune reactions against these novel biological modalities, referred to as immunogenicity, and no longer benefit from the treatments. In the current review, using Hemophilia A (HA) therapy as an example, we will discuss the immunogenicity issue of multiple biological modalities. Currently, the number of therapeutic modalities that are approved or recently explored to treat HA, a hereditary bleeding disorder, is increasing rapidly. These include, but are not limited to, recombinant factor VIII proteins, PEGylated FVIII, FVIII Fc fusion protein, bispecific monoclonal antibodies, gene replacement therapy, gene editing therapy, and cell-based therapy. They offer the patients a broader range of more advanced and effective treatment options, yet immunogenicity remains the most critical complication in the management of this disorder. Recent advances in strategies to manage and mitigate immunogenicity will also be reviewed.