New insights in mucopolysaccharidosis type VI: Neurological perspective

Objective: Mucopolysaccharidosis type VI is a rare autosomal recessive storage disorder, caused by deficiency of arylsulfatase B. Data on neurological involvement in mucopolysaccharidosis type VI patients under enzyme-replacement therapy are limited. This study explores the neurological and magnetic resonance imaging findings in a sample of mucopolysaccharidosis type VI patients receiving enzyme-replacement therapy. Methods: We performed a cross-sectional study including six patients with biochemical confirmation of mucopolysaccharidosis type VI and at least 105 consecutive weeks (two years) receiving intravenous enzyme-replacement therapy. The protocol included a comprehensive clinical examination, brain and spinal cord magnetic resonance imaging for all subjects. Results: Overall, cognition was spared, while we found presence of hearing impairment, increasing in deep tendon reflexes and deep sensation reduction in three patients. In addition to the classical abnormalities related to other types of mucopolysaccharidosis, imaging studies demonstrated morphological changes in anatomy of middle cranial fossa and sella shape. Even in asymptomatic or mild compromised patients, spinal cord compression was found. In four patients we noticed atlantoaxial joint subluxation and three had cervical spinal stenosis. Degenerative processes involving vertebral column, including discal protrusion and axis abnormalities, were present in all patients. Conclusions: Neuroaxis involvement was a universal finding and neurological examination might not predict the severity of the disease in course. Image studies should not be performed according exclusively clinical parameters for these patients, once we have demonstrated that neurological involvement may be silent in these patients.