Clinical variability of type II sialidosis by C808T mutation.

Sialidosis (McKusick 256550) is an autosomal recessive disorder resulting from mutations in the NEU gene, located in 6p21.3, which leads to deficiency of alpha-N-acetyl neuraminidase (sialidase) activity, causing an accumulation of its substrates, oligosaccharides, in the lysosomes of various organs and tissues and an increased presence in urine and other organic fluids. We present a clinical report of three patients diagnosed for type II sialidosis. The first patient is a 12-year-old boy with the classic infantile form. His sister had a congenital form of sialidosis and died at 20 months of age. The third, nonrelated patient presented shortly after 1 year of age and had borderline cognitive delay at 9 years. All three patients were homozygous for the C808T mutation of the NEU gene. Their ancestors originated from a small area to the east of the city of Seville (Spain), suggesting the existence of a Seville founder mutation.