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biotech/news//NJ.com
Jason and Justin Leider have mucopolysaccharidosis type II, also known as Hunter syndrome.
The FDA approved Avlayah, the first new Hunter syndrome treatment in nearly 20 years, in March.
KEY POINTS
Avlayah received FDA approval only for patients up to age 16 years, 364 days.
Off-label Avlayah prescriptions for those over 16 are unlikely to be covered by insurance.
In clinical trials, Avlayah reduced cerebrospinal fluid heparan sulfate levels by 91%.
Future expansion of Avlayah approval to older patients could take 5-10 years, risking patient lives.
Jeff and Deena Leider have been in the fight of their lives for the last 15 years, ever since their sons Jason and Justin were diagnosed as toddlers with a rare, progressive disease that causes early death.
The siblings, who grew up in Bergen County, have mucopolysaccharidosis type II, also known as Hunter syndrome. It’s an extremely rare genetic disorder that affects fewer than 500 people in the United States, mostly males, according to the Food and Drug Administration.
People with the condition lack an enzyme that the body needs to digest sugar, causing it to build up in the body. This buildup can cause progressive physical and mental decline, according to the National Organization for Rare Diseases. There’s no cure.
“We have this cloud over us,” said Jeff Leider in a phone interview.
He thought the skies might finally be clearing in March when the FDA approved Avlayah, a new drug developed by Denali Therapeutics to treat the neurologic complications of Hunter syndrome.
“I started crying hysterically,” he said. “I thought our fight was over.”
But the family soon learned the FDA implemented an age cap for the drug: 16 years and 364 days old. Jason turned 19 in August 2025 and Justin turned 17 in February, missing the cutoff by 29 days.
“When is that cloud going to be lifted off of us?” Deena Leider asked aloud.
Deciding who lives and who dies
In family photos, Jason and Justin seem like normal teenagers, wearing Yankee gear and youth baseball T-shirts. But even their physical characteristics are a hallmark sign of Hunter syndrome. People with the disorder often have short stature, a broad chest and distinct facial features.
Hunter syndrome is classified into severe and mild types. Both Leider brothers have severe forms of the illness, but progression of the disease can still vary greatly.
At 19 years old, Jason is nonverbal and has already had 15 surgeries, including a 2024 procedure to reinforce his trachea, which started to collapse as a result of disease progression.
Justin, 17, can shower himself, cook his own food and drive a car. While he’s more independent, his health remains fragile. He’s had a dozen surgeries over the years, including two on his back; spinal deformities and spine stiffness are not uncommon for people with Hunter syndrome.
Despite relocating to Florida in 2024, the family still makes monthly trips to New Jersey, where the brothers receive an enzyme replacement therapy at Hackensack Meridian Health’s Hackensack University Medical Center.
During one of these routine visits in January, Justin sustained a spinal cord injury that caused a temporary loss of movement in his legs. He had to relearn how to walk.
“That’s just the tip of the iceberg of what we’ve been going through the past 15 years,” said Jeff Leider.
Ever since the kids were diagnosed, Jeff Leider has been their tireless advocate. He influenced New Jersey lawmakers to pass the “Let Them Be Little Act” in 2014, which requires screening of newborns for mucopolysaccharidosis type I and II.
Now, he’s advocating for his children to gain access to a potentially life-changing medication.
Avlayah is the first new FDA-approved treatment for Hunter syndrome in nearly 20 years. It offers hope for families facing the grim diagnosis. In a clinical trial, the drug demonstrated a 91% reduction in cerebrospinal fluid heparan sulfate levels — a key indicator of disease severity.
However, the medication is currently only approved for patients up to the age of 16. While it can be prescribed off-label to people above 16, insurance may not cover it.
In an email to NJ.com, the Department of Health and Human Services stated the “FDA bases approval decisions on whether an application” demonstrates “that it is safe and effective for use under the conditions in its proposed labeling.”
“This includes a benefit-risk assessment based on the data presented in each application.”
In a LinkedIn post, the National MPS Society said that while FDA approval is a victory, “we also recognize that our work is far from over. Every child, every family, and every rare disease community deserves access to safe, effective treatments without delay.”
It doesn’t seem fair to the Leider family.
“They are potentially playing God with who gets the meds and who doesn’t,” Jeff Leider said. “No one should be deciding who lives and who dies.”
The medication may eventually be approved for older patients. But by that time, Jeff Leider said it may be too late.
“We’re talking 5-10 years away. These kids don’t have 5-10 years,” said Jeff Leider. “It’s going to be a slow progression. A gruesome, horrible death. That could all be avoided if the FDA would just get rid of this age cap.”