4 Rare Diseases Could Get Their First Treatment This September

September 2026 was a crowded month for rare disease decisions. The FDA had 8 rare disease decisions due between September 19th and September 30th, and it approved all 8 by the end of the month, 6 of them ahead of their action dates. Of the conditions involved, 4 (Sanfilippo syndrome type A, Alexander disease, ataxia-telangiectasia, and MCT8 deficiency) had never had an approved treatment of any kind, and each one now has its first.

Behind each date is a community that has measured its waiting in decades, not months. Here is what was approved, who each label covers, and what families should know now that the decisions are in.

Why September 2026 Is a Landmark Month for Rare Disease Approvals

A PDUFA date is the deadline by which the FDA has committed to finish reviewing a drug application, set under the Prescription Drug User Fee Act. The agency does not publish these dates. Drug companies usually disclose them when the FDA accepts an application, which is why they arrive scattered across press releases and investor filings rather than in one official list. Trial Friend gathers every rare disease date, with its source, on our FDA decision calendar.

Clusters of decision dates happen, and this one was tight. Applications accepted in early 2026, under priority review or as resubmissions with a 6-month clock, stacked their deadlines into a single 12-day window. The result was that 4 diseases with zero approved treatments each learned their outcome before the month ended, and all 4 got an approval.

UX111 for Sanfilippo syndrome type A (approved September 17th as Fayuvi). Ultragenyx's one-time AAV9 gene therapy became the first approved treatment in the history of a disease that affects an estimated 3,000 to 5,000 patients in Ultragenyx's planned markets, by the company's count, and, according to Ultragenyx, has a median life expectancy of 15 years. Ultragenyx said the FDA's 2025 rejection cited manufacturing and facility issues, not the clinical data, and that the resubmission included up to 8 years of follow-up data. We covered the full UX111 story, and families can find enrolling studies on our Sanfilippo syndrome page.

“cannot come soon enough for families facing this devastating diagnosis”

Emil D. Kakkis, M.D., Ph.D., CEO of Ultragenyx, on the FDA's acceptance of the resubmission, April 2026

Aqneursa for ataxia-telangiectasia (approved September 18th, 1 day early). IntraBio's levacetylleucine, already approved for Niemann-Pick disease type C, became the first approved therapy for ataxia in ataxia-telangiectasia, a genetic disease that combines progressive loss of coordination with immune deficiency and cancer risk. The approval covers adults and children weighing at least 15 kg and rests on a 73-patient placebo-controlled crossover study; the decision page carries the FDA notice.

Zilganersen for Alexander disease (approved September 3rd as Zanvastro, 19 days early). Ionis built an RNA-targeted medicine for Alexander disease, a very rare leukodystrophy. Ionis reported that in its pivotal study, zilganersen held gait speed steady at week 61 compared with the control group. Approval gave Alexander disease its first FDA-approved treatment.

Emcitate for MCT8 deficiency (September 28th). Egetis Therapeutics' tiratricol treats a rare genetic disorder in which thyroid hormone cannot enter the cells that need it, causing severe developmental impairment in boys. The FDA approved it on September 28th, the first treatment for the disease; the approval covers the body's thyroid hormone excess, not the developmental disability.

SMA, FOP, and Cholangiocarcinoma Gained New Treatment Options

Apitegromab for spinal muscular atrophy (approved September 11th as Isembyld, 19 days early). Scholar Rock's muscle-targeted antibody, covered in full here, is designed to work alongside the SMN-directed therapies that transformed SMA care, and Scholar Rock says it targets the muscle weakness those drugs do not fully resolve.

Zilurgisertib for fibrodysplasia ossificans progressiva (approved September 25th as Atebrioz, 1 day early). FOP, in which the body grows a second skeleton of bone through muscle and tendon, received its first antibody treatment in August when the FDA approved Pasatru for adults, 3 years after Sohonos became the first approved FOP drug. Atebrioz, a once-daily oral ALK2 inhibitor from Mirum and Incyte approved for patients 12 and older, is now the third option for people with FOP, estimated at about 280 Americans in a 2021 study whose authors said the true number may be higher. Mirum and Incyte said on September 25th that they expect Atebrioz to be available in the US in October through the Mirum Access Plus program.

Lirafugratinib for cholangiocarcinoma (approved September 23rd as Lyrfigtu, a few days early). Elevar's lirafugratinib is designed to block FGFR2 selectively, and it treats the fusion-driven form of bile duct cancer. Elevar has given both September 25th and September 27th as its action date, set when the FDA granted priority review. Our Lyrfigtu coverage has the trial results and label warnings.

Camzyos for adolescents with obstructive hypertrophic cardiomyopathy (September 30th). Bristol Myers Squibb's mavacamten was already approved for adults; on September 30th the FDA extended it to children who weigh at least 30 kg.

What Happens on a PDUFA Date and What Can Still Go Wrong

Each of these dates can end in 1 of 3 outcomes: an approval, a rejection known as a complete response letter, or an extension if the FDA needs more time to review new information. Decisions also arrive early more often than people expect. This month proved it: 6 of the 8 September decisions came before their action dates, Zanvastro and Isembyld by 19 days each. In August, the FDA approved Lisraya for dermatomyositis on August 27th, more than a month before the end of the third-quarter window its sponsor had given.

A rejection is not an ending. Some complete response letters concern manufacturing rather than the clinical data, according to the companies that received them. On this year's rare disease calendar, UX111 and apitegromab this month and the acromegaly therapy Oclaiz in December had all been rejected before, Oclaiz twice, and both September resubmissions ended in approval. Extensions happen too: Capricor's Duchenne cell therapy Deramiocel saw its date pushed from August to November 22nd this year.

September Capped a Busy Year for Rare Disease FDA Approvals

September followed a year with many rare disease approvals, including Pasatru, a second FOP treatment for adults, in August, and several came ahead of their action dates. The FDA calendar keeps the full list of recent decisions with a source for each one.

What Families Should Do After a Rare Disease FDA Approval

Talk with your specialist about the label itself. Approvals often come with narrower labels than communities hope for. UX111's label covers Sanfilippo type A only, and only children with preserved neurodevelopmental function; Atebrioz's label covers patients 12 and older, Isembyld is only for patients 2 and older already on an SMN2-targeted therapy, and eligibility details like age, disease stage, or prior treatment can determine whether an approval applies to your family at all.

Expect a gap between approval and access. Insurance coverage decisions, specialty pharmacy setup, and, for gene therapies, qualified treatment center designations typically take weeks to months after an approval. Many companies open patient support programs within days of the decision, and enrolling early can help families start sooner.

A rejection does not close every door. After a complete response letter, some companies keep expanded access programs running, trials for these conditions keep enrolling, and many companies resubmit. Our Match Me tool can check a patient's profile against actively enrolling studies for any of the diseases in this roundup.