Mucolipidosis type IV is an inherited recessive disorder characterized by delayed development and progressive vision loss. Approximately 95 % of individuals with this condition have the severe from, typical mucolipidosis IV, and the remaininding 5% have the milder form, atypical mucolipidosis IV. People with typical mucolipidosis IV have psychomotor delay (delayed development of mental and motor skills). Patients with mucolipidosis IV show progressive visual impairment during the first decade as a result of a combination of corneal clouding and retinal degeneration. Mucolipidosis type IV is estimated to occur in 1 in 40,000 people.  About 70 percent of affected individuals have Ashkenazi Jewish ancestry. The MCOLN1 gene is the only gene known to be associated with mucolipidosis IV. Mutations in the MCOLN1 gene cause mucolipidosis type IV and mostly result in the production of a nonfunctional mucolipin-1protein or prevent the protein from being produced. A lack of functional mucolipin-1 impairs transport of lipids and proteins, causing these substances to build up inside lysosomes. Two mutations the MCOLN1 gene, c.406-2A>G and g.511_6944del (also known as 511del6434), account for 95% of mutations in individuals of Ashkenazi Jewish heritage.