4 Rare Diseases Could Get Their First Treatment This September

September 2026 was unlike any stretch in recent rare disease history. 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 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 happen, but not like this. 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 the countries where Ultragenyx expects to sell it and carries a median life expectancy of 15 years. The FDA rejected it in 2025 over manufacturing issues unrelated to whether it works, and the resubmission carries 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.

“The FDA's acceptance of the BLA for UX111 brings us closer to the possibility of a first-ever therapy for Sanfilippo syndrome Type A, a milestone that we recognize cannot come soon enough for families facing this devastating diagnosis.”

Emil D. Kakkis, M.D., Ph.D., CEO of Ultragenyx

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 a leukodystrophy so rare that most neurologists never see a case. In its pivotal study, zilganersen stabilized gait speed at week 61 in a disease defined by steady decline. Approval gave Alexander disease its first disease-modifying therapy.

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, addressing 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 cleared 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 the roughly 300 Americans living with FOP. Mirum expects it to be available in the US in October.

Lirafugratinib for cholangiocarcinoma (approved September 23rd as Lyrfigtu, 2 days early). Elevar's selective FGFR2 inhibitor targets the fusion-driven form of bile duct cancer, where precision in hitting FGFR2 without nearby targets has been the field's persistent challenge. Its action date, set when the FDA granted priority review, was September 25th. 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. Complete response letters frequently concern manufacturing or paperwork rather than the science. On this year's rare disease calendar, UX111 and apitegromab this month and the acromegaly therapy Oclaiz in December were all on their second trip through the process after earlier rejections, 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 Caps the Busiest Rare Disease Approval Year in Memory

The crowded month is not an accident of scheduling. It caps a year in which the FDA has moved through rare disease applications at a remarkable clip: by CheckRare's tracking, more than 35 orphan drug approvals and label expansions have already cleared in 2026, from the first Menkes disease treatment in January to a second FOP treatment, Pasatru, in August. Several arrived ahead of schedule, and the agency's national priority voucher program has produced same-year reviews that once took a decade.

For rare disease families, the pace matters more than any single date. An agency willing to approve a gene therapy early, or to clear 2 first-ever treatments in a single week, is an agency whose posture toward small patient populations has shifted. September is the most visible test of that posture yet.

What Families Should Do Before a Decision Day

Talk with your specialist now, not after the announcement. 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. Most companies open patient support programs within days of the decision; enrolling early usually means earlier treatment.

A rejection does not close every door. Companies with complete response letters often continue expanded access programs, trials for these conditions keep enrolling, and resubmissions typically follow within a year. Our Match Me tool can check a patient's profile against actively enrolling studies for any of the diseases on this month's docket.