Sanfilippo syndrome, often described as a form of childhood dementia, is a rare genetic disorder that gradually destroys a child's ability to speak, learn, and walk. Children with the condition initially develop normally, but as the disease progresses, they experience behavioural problems such as hyperactivity, anxiety, and difficulty sleeping. Eventually, they lose their speech and mobility, and most die in their teens.
The condition is caused by a genetic mutation that prevents the enzyme sulfamidase from breaking down complex sugar molecules. These molecules accumulate in the brain and nervous system, causing devastating developmental impacts. Sanfilippo affects approximately one in every 70,000 births, though experts believe the true prevalence may be higher.
Two-year-old Leni Forrester from Sevenoaks, Kent, was diagnosed with Sanfilippo syndrome type B before she showed any symptoms. Her parents, Emily and Gus, discovered the condition after routine genetic screening for Emily's sister flagged a rare gene. Despite the odds being incredibly low, both parents were carriers. Subtle early signs in Leni included bushy eyebrows, thick eyelashes, full lips, and talipes (feet turning inward).
Emily explained that because the condition is so rare, most children are only diagnosed after significant loss of cognitive and motor skills, with initial symptoms often misdiagnosed as autism or ADHD. The Cure Sanfilippo Foundation notes that early signs are usually present in the newborn period but may not be recognised until ages one to six. Families are often reassured that the child will “grow out of it.”
There are four subtypes of Sanfilippo – A, B, C, and D – each corresponding to a different enzyme deficiency. Type A is the most common and severe, while type B may progress less rapidly. Leni has type B. Her parents are urgently fundraising for research into potential cures, as two experimental treatments are stuck in clinical trials. They highlight that pharmaceutical companies have little financial incentive to develop treatments for such rare conditions.
