RAB18 deficiency causes two disorders with similar signs and symptoms; Warburg micro syndrome and Martsolf syndrome. Both of these diseases are considered to be part of the same disease spectrum because of similar features and shared genetic cause. Manifestations include eye problems from birth including cataracts, microphthalmia and microcornea, intellectual disability, delayed development hypotonia, spasticity and joint contractures. Martsolf syndrome affects the same body systems as Warburg micro syndrome but is usually less severe. RAB18 deficiency is caused by mutations in the RAB3GAP1, RAB3GAP2, RAB18, or TBC1D20 gene.