Experts say early diagnosis is the beginning of a cure, but the reality of rare diseases is not so simple.

Rare diseases are often delayed in diagnosis because their early symptoms are often mistaken for typical developmental delays or behavioral problems. Many inherited rare diseases, in particular, are characterized by normal development for the first few years of life, followed by progressively degenerative symptoms. Hence, it's not uncommon for a diagnosis to take years on average.

Mucopolysaccharidosis is one of the most common conditions to go undiagnosed because it may initially look like simple speech delays, attention deficits, or hyperactivity. However, even a year or two earlier diagnosis can have real benefits in preserving physical function, slowing disease progression, and potentially participating in clinical trials.

Mucopolysaccharidosis is a type of lysosomal storage disease in which certain enzymes required for normal metabolism are deficient. This causes glycosaminoglycans (GAGs) to accumulate in tissues and lead to dysfunction in various organs.

Depending on the deficient enzyme, there are seven recognized types of mucopolysaccharidosis, numbered 1 through 7. The common symptoms of mucopolysaccharidosis include facial changes (such as broad, flat noses and thick lips), growth retardation, and joint stiffness, but each type has different symptoms and progression rates.

Notably, type 3 is characterized by an early decline in intelligence and behavioral problems compared to other types, while types 4 and 6 may retain intelligence but have severe physical deformities. In Korea, Hunter syndrome, type 2, is the most frequent, followed by Sanfilippo syndrome, type 3.

There are three types of mucopolysaccharidoses for which treatments are available: 1, 2, and 4A, and 6 and 7. It is recommended that anyone suspected of having mucopolysaccharidosis be tested as soon as possible. Attention to development is key to accessing early treatment.

Mucopolysaccharidosis can be diagnosed using urine and blood tests to measure GAG accumulation and enzyme activity, and imaging tests, such as X-rays, ultrasounds, and MRIs, can be used to look for abnormalities in the spine, organs, and more.

Sanfilippo syndrome is a mucopolysaccharidosis type 3, which is divided into four types (types A through D), with type A being the most advanced and severe form. It is difficult to diagnose early because children do not show any apparent symptoms immediately after birth and appear to develop normally.

However, language delays and developmental stagnation usually appear between the ages of two and five, accompanied by symptoms including hyperactivity, attention deficit, and sleep disturbances. Over time, cognitive decline, motor weakness, spasticity, and respiratory problems also occur, eventually leading to the need for assistance with daily activities, such as eating, mobility, and communication.

The rate of progression varies, but in most cases, severe and life-threatening complications occur in adolescence or early adulthood.

There is no cure, but public and rehabilitative care is provided through physical therapy, speech therapy, and special education to alleviate symptoms. Clinical trials of various approaches, including gene therapy and enzyme replacement therapy (ERT), are underway, raising hopes for future treatments.

Although Sanfilippo syndrome type A is a very rare and fatal genetic disorder, early diagnosis and consistent management can slow the progression of symptoms and improve the quality of life of your child. If your child has delayed language development, hyperactivity, or sleep problems, the best first step is to visit your local rare disease center or university hospital for a consultation with a specialist rather than dismissing it as a simple developmental delay.

"With Sanfilippo syndrome type A, time is of the essence. In cases of rapid progression, delayed diagnosis can be fatal to a child's health, so it is crucial to get tested early if you suspect symptoms,” said Professor Cho Sung-yoon of the Department of Pediatrics at Samsung Medical Center, stressing the importance of early diagnosis. “In addition, it has recently become possible to diagnose mucopolysaccharidosis type 1 in early screening tests for newborns, and we look forward to including more types of mucopolysaccharidosis tests in the future."

Information on clinical trials underway in Korea for Sanfilippo syndrome type A can be checked in real-time through the Ministry of Food and Drug Safety's (MFDS) drug info site.