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Last updated:
August 11, 2015
Years published: 1986, 1988, 1990, 1995, 1996, 1997, 1998, 1999, 2002, 2014
NORD gratefully acknowledges Abraham Yu, NORD Editorial Intern from the University of Notre Dame, and Ehud Goldin, PhD, Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, for assistance in the preparation of this report.
Mucolipidosis IV is a rare metabolic disorder characterized by intellectual disability; severe impairment in the acquisition of skills requiring the coordination of muscular and mental activities (psychomotor retardation); diminished muscle tone (hypotonia); clouding (opacity) of the clear portion of the eyes through which light passes (cornea); and progressive degeneration of the nerve-rich membrane lining the eyes (retinal degeneration). Mucolipidosis IV is inherited as an autosomal recessive genetic trait and caused by mutations in the MCOLN1 gene.
The severe form of the disease is called typical mucolipidosis IV, and the mild form is called atypical mucolipidosis IV. Approximately 95 percent of individuals diagnosed with this condition have the severe form.
The symptoms and physical findings associated with mucolipidosis IV are usually apparent within three to eight months following birth. The first recognized symptoms are usually clouding (opacity) of the cornea and eye movement abnormalities. In some cases, these symptoms may be overlooked until three to five years of age.
Most affected infants exhibit hypotonia, moderate to severe intellectual disability, delays in reaching developmental milestones, and/or significant psychomotor retardation.
In addition, individuals with mucolipidosis IV may have abnormalities affecting the eyes including crossed eyes (strabismus), puffy eyelids, degeneration of the nerve-rich membrane lining the eyes (retina), and/or visual impairment (amblyopia) in an eye that appears structurally normal. In some cases, such eye abnormalities may result in an abnormal sensitivity to light (photophobia) and/or nearsightedness (myopia).
Individuals with mucolipidosis IV develop iron deficiency anemia because their stomachs do not secrete acid. They do not have enlarged livers or spleens, skeletal involvement, or mucopolysaccharides in the urine.
Patients exhibit accumulation of certain fatty substances (lipids) and certain complex carbohydrates (mucopolysaccharides) within the cells of many tissues of the body. Those appear as large vacuoles and fluorescent vesicles in patient cells.
Mucolipidosis IV is inherited as an autosomal recessive genetic trait. The responsible gene has been isolated and its protein-product, as well as its chromosomal location, determined. The gene, designated MCOLN1, has been tracked to 19p13.3-p13.2 where it encodes for the mucolipin-1 protein. Mutations in this gene result in a deficiency of transport channel receptor protein. The exact function of this protein is still unknown. The effect of mutations on patient and animal model cells indicates a loss of regulation on intracellular traffic which eventually affects various tissue functions.
Chromosomes are found in the nucleus of all body cells. They carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males and two X chromosomes for females. Each chromosome has a short arm designated as p and a long arm identified by the letter q. Chromosomes are further subdivided into bands that are numbered. For example, chromosome 11p15.4 refers to band 15.4 on the short arm of chromosome 11.
Recessive genetic disorders occur when an individual inherits two copies of an abnormal gene for the same trait, one from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
All individuals carry 4-5 abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Mucolipidosis IV is a rare inherited metabolic disorder that affects males and females in equal numbers. The disorder was first identified in 1974 and as of 2010, 70 cases have been reported in the medical literature. The precise incidence is unknown, but is estimated to be approximately 1:40,000. About 70% of those diagnosed are of Ashkenazi Jewish ancestry.
Mucolipidosis IV may be suspected based upon a thorough clinical examination, a detailed patient history, and a variety of specialized tests. Individuals with mucolipidosis IV present with iron deficiency anemia, high serum gastrin levels and characteristic findings on brain MRI examinations. In most cases, an electron microscope is used to visualize characteristic lysosomal storage bodies in fibroblasts obtained from biopsied tissue of the skin and/or the delicate membrane that lines the eyes (conjunctiva). Molecular genetic testing for mutations in the MCOLN1 gene is available to confirm the diagnosis.
Treatment
Treatment of mucolipidosis IV is symptomatic and supportive. Symptoms associated with clouding of the corneas may be treated by the use of contact lenses and/or artificial tears. Intense physical, occupational and speech therapy are also of benefit. Iron replacement is utilized for those with anemia.
Genetic counseling is recommended for affected individuals and their families.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.
For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov
For information about clinical trials sponsored by private sources, contact:
www.centerwatch.com
For information about clinical trials conducted in Europe, contact:
https://www.clinicaltrialsregister.eu/
TEXTBOOKS
Scriver CR, et al., eds. The Metabolic and Molecular Basis of Inherited Disease. 7th Ed. New York, NY; McGraw-Hill Companies, Inc; 1995:36, 374.
Menkes JH, au, Pine JW, et al., eds. Textbook of Child Neurology, 5th ed. Baltimore, MD: Williams & Wilkins; 1995: 86-87.
REVIEW ARTICLES
Bach G. Mucolipidosis type IV. Mol Genet Metab. 2001;73:197-203.
Pshezetsky AV, Ashmarina M. Lysosomal multienzyme complex: biochemistry, genetics, and molecular pathophysiology. Prog Nucleic Acid res Mol Biol. 2001;69:81-114.
Mancini GM, Havelaar AC, Verheijen FW. Lysosomal transport disorders. J inherit Metab Dis. 2000;23:278-92.
JOURNAL ARTICLES
Geer J, Skinner S, Goldin E, Holden K, et al. Mucolipidosis Type IV: A Subtle Pediatric Neurodegenerative Disorder. Pediatr Neurol. 2010; 42(3): 223-2336.
Altarescu G, et al., The neurogenetics of mucolipidosis type IV. Neurology. 2002;59:306-13.
Acierno JS Jr, Kennedy JC, Falardeau JL, et al. A physical and transcript map of the MCOLN1 hene region on human chromosome 19p13.3-p13.2. Genomic. 2001;73:203-10.
Bargal R, Avidan N, Olender T, et al. Mucolipidosis type IV: novel MCOLN1 mutations in Jewish and non-Jewish patients and the frequency of the disease in the Ashkenazi Jewish population. Hum Mutat. 2001;17:397-402.
Wang ZH, Zeng B, Pastores GM, et al. Rapid detection of two common mutations in Ashkenazi Jewish patients with mucolipidosis type IV. Genet Test. 2001;5:87-92.
Bargal R, Avidan N, Ben-Asher E, et al. Identification of the gene causing mucolipidosis type IV. Nature Genet. 2000,26:120-123.
Sun M, Goldin E, Stahl S, et al. Mucolipidosis type IV is caused by mutations in a gene encoding a novel transient receptor potential channel. Hum Mol Genet. 2000;9:2471-78.
Slaugenhaupt SA, et al., Mapping of the mucolipidosis type IV gene to chromosome 19p and definition of founder haplotypes. Am J Med Genet. 1999;65:773-8.
Raas-Rothschild A, Bargal R, Dellapergola S, et al. Mucolipidosis type IV: the origin of the disease in the Ashkenazi-Jewish population. Europ J Hum Henet. 1999;7:496-498.
Chen C-S, Bach G, Pagano RE. Abnormal transport along the lysosomal pathway in mucolipidosis, type IV disease. Proc Nat Acad Sci. 1998;95:6373-78.
Bargal R, Bach G. Mucolipidosis type IV: abnormal transport of lipids to lysosomes. J inherit Metab Dis. 1997;20:625-32.
INTERNET
Schiffmann R, Slaugenhaupt SA, Smith J, et al. Mucolipidosis IV. 2005 Jan 28 [Updated 2010 Jul 20]. In: Pagon RA, Adam MP, Bird TD, et al., editors. GeneReviews[Internet]. Seattle (WA): University of Washington, Seattle; 1993-2014. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1214/ Accessed May 19, 2014.
McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). Baltimore. MD: The Johns Hopkins University; Available at https://omim.org/entry/252650 Entry No: 252650; Last Update:08/06/2010. Accessed May 19, 2014.
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