RAB18 deficiency

RAB18 deficiency causes two conditions with similar signs and symptoms that primarily affect the eyes, brain, and reproductive system. These two conditions, called Warburg micro syndrome and Martsolf syndrome, were once thought to be distinct disorders but are now considered to be part of the same disease spectrum because of their similar features and shared genetic cause.

Warburg micro syndrome is the more severe condition. Individuals with this condition have several eye problems from birth, including clouding of the lenses of the eyes (cataracts), abnormally small eyes (microphthalmia), and small corneas (microcornea). The lens is a structure at the front of the eye that helps focus light, and the cornea is the outer covering of the eye. In addition, the pupils of the eyes may be abnormally small (constricted), and they may not enlarge (dilate) in low light. Individuals with Warburg micro syndrome also have degeneration of the nerves that carry visual information from the eyes to the brain (optic atrophy). The eye problems impair vision in affected individuals.

People with Warburg micro syndrome have severe intellectual disability and other neurological features due to problems with growth and development of the brain. Affected individuals have delayed development and may never be able to sit, stand, walk, or speak. They usually have weak muscle tone (hypotonia) in infancy. By early childhood, they develop muscle stiffness (spasticity) and joint deformities (contractures) that restrict movement in the legs. The muscle problems worsen (progress) to include the arms and lead to paralysis of all four limbs (spastic quadriplegia). Eventually, breathing may be impaired. The brain abnormalities can contribute to vision problems (cortical visual impairment). Individuals with Warburg micro syndrome may also have recurrent seizures (epilepsy).

Some people with Warburg micro syndrome have reduced production of the hormones that direct sexual development (hypogonadotropic hypogonadism). The shortage of these hormones impairs normal development of reproductive organs. Affected males may have a small penis (micropenis) or undescended testes (cryptorchidism). Affected females may have underdeveloped internal genital folds (labia minora) or a small clitoris or vaginal opening (introitus).

Martsolf syndrome affects the same body systems as Warburg micro syndrome but is usually less severe. Individuals with Martsolf syndrome have cataracts, microphthalmia, and small pupils. They have milder optic atrophy and cortical visual impairment than people with Warburg micro syndrome. Intellectual disability is mild to moderate in people with Martsolf syndrome. While language and motor skills, such as sitting and walking, are delayed, affected individuals usually acquire them. Hypotonia is common in infants with Martsolf syndrome, although spasticity worsens more slowly than in individuals with Warburg micro syndrome, and it usually affects only the legs and feet. Hypogonadotropic hypogonadism can also occur in individuals with Martsolf syndrome.

Neither Warburg micro syndrome nor Martsolf syndrome affect the life expectancy of affected individuals.