What Your Test Results Mean:

Carriers typically show no symptoms of ML IV; however, carriers are at an increased risk of having a child with ML IV. Risk for the current or future pregnancies is dependent on your partner’s carrier status.

Disease Explained:

ML IV is an inherited metabolic disorder in which harmful amounts of fats and proteins accumulate within the lysosomes, or recycling compartments, of cells in the body. Individuals with ML IV do not produce enough of one of the proteins, mucolipin-1, which is needed to properly dispose of fats and proteins in the body. Over time, this excessive build-up of fats and lipids within the lysosomes causes developmental delay, visual impairment, and other signs of the disease.

There are two forms of ML IV. In the most common form, typical ML IV, developmental delays are noted in the first year of life. Maximal developmental level achieved is typically 18 months of age. Neurodegeneration is seen in approximately 15% of individuals with typical ML IV. By the teens, severe vision loss or blindness caused by corneal clouding or progressive retinal degeneration is present in most individuals. Additional characteristics of the disease include impaired stomach acid production causing elevated gastrin in the blood as well as iron deficiency that can lead to anemia. Individuals with the more mild form, atypical ML IV, have milder delays and eye abnormalities than those with typical ML IV.

Treatment of individuals with ML IV typically includes supportive therapies and iron supplementation for iron deficiency anemia. Life expectancy is may be shortened but individuals with ML IV typically live into adulthood.

How the Genetics Works:

The clinical features of ML IV can be explained by pathogenic variants in the MCOLN1 gene. In general, individuals have two copies of the MCOLN1 gene. Carriers of ML IV have a single variant in one copy of the MCOLN1 gene while individuals with ML IV have variants in both copies of their genes, one inherited from each parent.