Rare-Disease Gene Therapy Research

What published trials and FDA records show for gene therapies in rare inherited diseases such as spinal muscular atrophy, inherited retinal disease and hemophilia B, and where the limits are.

Content last updated October 22, 2026. This page has not been medically reviewed.

Quick answer

Rare inherited diseases are where gene therapy has its clearest human results so far. Several products are FDA-approved for specific conditions, and some trials show large effects. But each result belongs to one product, one disease and one population. This page is information only, not medical advice. Anyone considering a gene therapy should talk with a specialist at a treatment center.

What "gene therapy" means here

The FDA describes human gene therapy as seeking to modify or manipulate the expression of a gene, or to alter the biological properties of living cells, for therapeutic use. [1] One approach replaces a faulty gene with a working copy. [1] Gene therapy products are regulated by the FDA's Center for Biologics Evaluation and Research, and marketing one requires an approved biologics license application. [1] For the technology itself, see gene addition and gene therapy explained and viral vectors in gene therapy.

Examples with human trial data

These are examples, not a complete list and not recommendations. The FDA keeps a current list of licensed cellular and gene therapy products. [2]

Condition	Product (US status)	What the cited trial measured	Evidence label
Spinal muscular atrophy (SMA)	Zolgensma; FDA indication is pediatric patients under two years old with bi-allelic SMN1 mutations [3]	Sitting and survival without permanent ventilation, single-arm, compared with an outside untreated group	Approved medicine
RPE65-related inherited retinal disease	Luxturna; FDA indication is confirmed biallelic RPE65 mutation-associated retinal dystrophy [4]	Mobility at different light levels, randomized	Approved medicine
Hemophilia B	Hemgenix is on the FDA licensed list [2]	Bleeding rate against the same patients' earlier factor IX prophylaxis	Approved medicine (see trial note)
Metachromatic leukodystrophy	Lenmeldy is on the FDA licensed list [2]	Motor function compared with an untreated history group	Approved medicine (see trial note)

What the trials found

Spinal muscular atrophy. In the STR1VE trial, an open-label, single-arm study, 22 infants with symptomatic type 1 SMA received one infusion. Thirteen (59%) sat independently for 30 seconds or longer at the 18-month visit, compared with 0 of 23 untreated infants in a natural-history group, and 20 (91%) survived without permanent ventilation at 14 months compared with 6 of 23 (26%). [5] Three serious adverse events were related or possibly related to treatment, including raised liver enzymes in two patients and hydrocephalus in one. [5] The comparison group was not randomized, and the trial was funded by the manufacturer. [5]

Inherited retinal disease. In a randomized, open-label phase 3 trial of voretigene neparvovec, 31 people were enrolled. The mean mobility change score was 1.8 light levels in the treated group versus 0.2 in controls after one year, and the trial reported no product-related serious adverse events. [6] A follow-up reported that improvements were maintained up to three to four years, and one treated patient had a retinal detachment at about year four. [7]

Hemophilia B. In the HOPE-B phase 3 study, 54 men received one infusion. The annualized bleeding rate fell from 4.19 in the lead-in period to 1.51 after treatment, with no treatment-related serious adverse events reported. [8] This was a single-group design that compared people with their own earlier period.

Metachromatic leukodystrophy. In a phase 1/2 study with 29 children, 26 were alive at a median follow-up of about 3.2 years, and motor function scores were higher than in matched untreated children. [9] All treated patients had at least one grade 3 or higher adverse event, mostly related to conditioning or the underlying disease. [9]

How to read a rare-disease gene therapy claim

Which exact product, and which exact mutation or disease form?
Was there a randomized control, or only a comparison with outside historical data?
Was the outcome something people notice (sitting, mobility, bleeding) or only a lab level?
How long were people followed, and what were the serious adverse events?
Is the product approved for that use, or only studied in a trial?

Frequently asked questions

Is gene therapy for rare diseases approved?

Some products are, for specific uses. For example, the FDA indication for Zolgensma is pediatric patients under two years old with SMA with bi-allelic SMN1 mutations. [3] Approval for one use does not cover other diseases.

Do gene therapies cure rare diseases?

The trials above measured specific outcomes over specific follow-up periods, such as survival without permanent ventilation or bleeding rate. [5] [8] They do not show a lifetime cure. Follow-up is still ongoing for many products.

Are the results of single-arm trials reliable?

They can show large changes, but without a randomized control the comparison relies on outside groups, which can differ from the treated group. The SMA trial compared treated infants with a natural-history cohort. [5]

What are the main risks?

They depend on the product. Reported risks include liver injury, immune reactions and, for some cell-based products, risks from chemotherapy conditioning. [10] [11] [9]

Where can I find trials?

Registered trials are listed on ClinicalTrials.gov, which the FDA points to for gene therapy trials. [12] See finding and understanding registered clinical trials.

More details: evidence, limits and cautions

The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.

How to read the evidence labels

Labels used on this page: approved medicine means a regulator has approved a named product for a named use. Promising but limited means human results exist but are small, uncontrolled, short or still being followed. Preclinical means cells or animals only. See how we label evidence.

Safety limits to know about

Immune and liver reactions. A review of high-dose systemic AAV gene therapy reports that fatalities have been observed from liver, kidney, heart or lung failure, with immune responses to the vector playing a role. [10] See immune responses to gene therapy.
A specific example. The FDA lists a boxed warning for acute serious liver injury and acute liver failure for Elevidys, and its indication is limited to ambulatory Duchenne muscular dystrophy patients with a confirmed DMD mutation. [11]
Conditioning. Some cell-based gene therapies require chemotherapy-type conditioning first, which brings its own risks. [9]
Follow-up is limited. Many trials are short compared with a lifetime. See off-target effects, durability and long-term monitoring.

Safety note

Results in one rare disease do not carry over to other conditions, and a clinic offering a "gene therapy" is not evidence it is approved. The FDA advises making sure any gene therapy being considered is either FDA-approved or being studied under appropriate regulatory oversight. [12]

References

U.S. Food and Drug Administration. What is Gene Therapy? Read 2026-10-22.
U.S. Food and Drug Administration. Approved Cellular and Gene Therapy Products. Content current as of 09/17/2026. Read 2026-10-22.
U.S. Food and Drug Administration. ZOLGENSMA (product page). Read 2026-10-22.
U.S. Food and Drug Administration. LUXTURNA (product page). Read 2026-10-22.
Day JW, et al. Onasemnogene abeparvovec gene therapy for symptomatic infantile-onset spinal muscular atrophy in patients with two copies of SMN2 (STR1VE). Lancet Neurol. 2021. PMID 33743238. Abstract read 2026-10-22.
Russell S, et al. Efficacy and safety of voretigene neparvovec (AAV2-hRPE65v2) in patients with RPE65-mediated inherited retinal dystrophy: a randomised, controlled, open-label, phase 3 trial. Lancet. 2017. PMID 28712537. Abstract read 2026-10-22.
Maguire AM, et al. Durability of Voretigene Neparvovec for Biallelic RPE65-Mediated Inherited Retinal Disease: Phase 3 Results at 3 and 4 Years. Ophthalmology. 2021. PMID 33798654. Abstract read 2026-10-22.
Pipe SW, et al. Gene Therapy with Etranacogene Dezaparvovec for Hemophilia B. N Engl J Med. 2023. PMID 36812434. Abstract read 2026-10-22.
Fumagalli F, et al. Lentiviral haematopoietic stem-cell gene therapy for early-onset metachromatic leukodystrophy: long-term results from a non-randomised, open-label, phase 1/2 trial and expanded access. Lancet. 2022. PMID 35065785. Abstract read 2026-10-22.
Lethal immunotoxicity in high-dose systemic AAV therapy. Mol Ther. 2023. PMID 37822079. Abstract read 2026-10-22.
U.S. Food and Drug Administration. ELEVIDYS (product page and latest safety information). Read 2026-10-22.
U.S. Food and Drug Administration. Information About Self-Administration of Gene Therapy. Content current as of 11/21/2017. Read 2026-10-22.

Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.