Mucolipidosis I: A type of mucolipidosis that is characterized by deficiency of the enzyme neuraminidase (sialidase). There are two forms of the disease. One form is characterized by cherry red spots in the eyes, gradual loss of vision, progressive debilitating myoclonus (muscle spasms), and normal intelligence. The other form of the disease, in addition to featuring the symptoms of the first form, causes a coarse face, bony abnormalities, and sometimes early death. Also known as sialidosis.