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  1. Mucolipidosis type IV (MLIV) is an autosomal recessive inborn error of intracellular membrane trafficking that is associated with lysosomal inclusions in a variety of cell types. An alteration in mucolipin-1, a transmembrane protein of the transient receptor potential channel family, causes MLIV.

  2. Most of the patients with MLIV have severe motor developmental delay, corneal clouding, progressive retinal degeneration, and achlorhydria. A few patients are less severely affected and exhibit variable general developmental delay, ataxia, and dysarthria together with the characteristic corneal clouding and retinal dystrophy. Notably absent are dysplastic bone abnormalities and enlargement of organs such as the liver and the spleen.

  3. MLIV is pan-ethnic, but most patients are of Ashkenazi-Jewish ancestry, in which the most prevalent mutation occurs at a frequency of approximately 1/100.

  4. The mucolipidosis type IV gene, MCOLN1, spans 12,300 base pairs on chromosome 19p13.3 and contains 14 exons. The product of this gene is called mucolipin-1, a 580-amino-acid protein with 6 transmembrane domains. This protein is thought to be a nonselective cation channel or a calcium channel, but its exact function is not yet completely understood.

  5. Two mutations, g.5534A→G and g.511-6944del, are present in 95% of all Ashkenazi-Jewish patients. Population-based screening for these mutations is useful for the identification and counseling of MLIV carriers. Identification of mutations in MCOLN1 should be used for prenatal diagnosis.

  6. The diagnosis of patients suspected of having MLIV can be strengthened by the finding of elevated blood gastrin. A skin biopsy showing lysosomal inclusions in almost every cell type can assist in the diagnosis. Identifying mutations in the MCOLN1 gene makes the definitive diagnosis.

  7. There is no specific treatment for patients with MLIV. A comprehensive rehabilitative approach can significantly improve quality of life.

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