SNP Shot: Genomic Insights

Mucolipidosis type IV is a genetic condition that causes developmental delays and progressive vision loss. It exists in two forms: a severe form, called typical mucolipidosis type IV, and a milder form, called atypical mucolipidosis type IV.

The severe form, typical mucolipidosis type IV, affects about 95% of individuals with the condition. Individuals with this form experience delays in mental and motor skill development (psychomotor delay), usually noticeable in the first year of life. These motor skills include abilities like sitting, standing, walking, grasping, and writing. The psychomotor delay can range from moderate to severe. Affected individuals often have intellectual disability, limited or absent speech, difficulty with chewing and swallowing, low muscle tone (hypotonia) that progresses to stiffness (spasticity), and problems with hand coordination. Most are unable to walk without assistance. In approximately 15% of cases, these psychomotor problems worsen over time.

While vision may be normal at birth for those with typical mucolipidosis type IV, it deteriorates during their first decade. They develop clouding of the cornea and progressive degeneration of the retina. By early adolescence, individuals with typical mucolipidosis type IV usually experience significant vision loss or blindness.

Individuals with typical mucolipidosis type IV also have impaired stomach acid production (achlorhydria). Though achlorhydria itself doesn't cause symptoms, it leads to elevated levels of gastrin, a hormone that regulates stomach acid production, in the blood. Iron deficiency and anemia are also possible. While people with severe mucolipidosis type IV often live into adulthood, their lifespan may be shorter.

About 5% of individuals have the milder form, atypical mucolipidosis type IV. These individuals generally have mild psychomotor delays and may learn to walk. They also tend to have less severe eye problems compared to those with the severe form. Achlorhydria may also be present in individuals with the atypical form.

Inheritance:

Mucolipidosis type IV follows an autosomal recessive inheritance pattern. This means that an affected individual must inherit a mutated copy of the responsible gene from both parents. The parents, who each carry one copy of the mutated gene, typically do not exhibit symptoms of the condition.