Sanfilippo syndrome, also known as mucopolysaccharidosis type III (MPS III), is a rare genetic disorder that primarily affects children. It belongs to a group of conditions called lysosomal storage disorders.

To understand what that means, think of the cells in your body as tiny, bustling cities. Each city has a recycling center that breaks down waste and old materials to keep things running smoothly. In our cells, these recycling centers are called lysosomes.

In a lysosomal storage disorder, a specific enzyme inside the lysosome is missing or doesn't work correctly. Without this crucial enzyme, the recycling center gets clogged. Certain materials can't be broken down, so they accumulate, or get "stored," inside the lysosome, eventually causing damage to the cell.

In Sanfilippo syndrome, the substance that builds up is a complex sugar molecule called heparan sulfate. This buildup is especially damaging to cells in the central nervous system, which is why the condition has such a profound impact on the brain.

Sanfilippo syndrome isn't a single disease but rather four different types, labeled A, B, C, and D. The specific type a person has depends on which enzyme is missing.

Children with Sanfilippo syndrome often appear healthy at birth and during early infancy. The first signs usually appear between the ages of two and six and are often behavioral.

The most devastating aspect of the disease is severe and progressive neurodegeneration. As heparan sulfate accumulates in brain cells, children experience a developmental standstill, followed by a gradual loss of skills they had already learned, like speaking and walking. Key clinical features include:

• Behavioral Issues: Hyperactivity, sleep disturbances, and challenging behaviors are common early signs.
• Cognitive Decline: Progressive loss of learning and memory, leading to severe intellectual disability.
• Physical Symptoms: While often less pronounced than in other MPS disorders, some children may have coarse facial features, an enlarged liver or spleen, and joint stiffness.

Over time, the damage leads to seizures, loss of mobility, and increasing dependence on caregivers for all daily needs. The progression is relentless, causing a cascade of neurological and physical problems.