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Mucolipidosis III alpha/beta
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Mucolipidosis III alpha/beta

Mucolipidosis III alpha/beta is a rare lysosomal storage disorder caused by mutations in the GNPTAB gene, leading to progressive skeletal, cardiac, and developmental abnormalities.

Overview

Mucolipidosis III alpha/beta is a disorder that affects many parts of the body. Signs and symptoms of this condition typically appear around age 3 and worsen slowly over time.

Individuals with mucolipidosis III alpha/beta grow slowly and have short stature. They also have stiff joints and dysostosis multiplex, which refers to multiple skeletal abnormalities seen on x‑ray. Many affected individuals develop low bone mineral density, which weakens the bones and makes them prone to fracture. Osteoporosis and progressive joint problems also cause bone pain that becomes more severe over time in people with mucolipidosis III alpha/beta.

People with mucolipidosis III alpha/beta often have heart valve abnormalities and mild clouding of the clear covering of the eye. Their facial features become slightly thickened or “over time.” Affected individuals may also develop frequent ear and respiratory infections. About half of people with this condition have mild intellectual disability or learning problems. Individuals with mucolipidosis III alpha/beta generally survive into adulthood, but they may have a shortened lifespan.

Frequency

Mucolipidosis III alpha/beta is a rare disorder, although its exact prevalence is unknown. It is estimated to occur in about 1 in 100,000 to 400,000 individuals worldwide.

Causes

Mutations in the GNPTAB gene cause mucolipidosis III alpha/beta. This gene provides instructions for making a part (subunit) of an enzyme called GlcNAc-1-phosphotransferase. This enzyme helps prepare certain newly made enzymes for transport to lysosomes. Lysosomes are compartments within the cell that use digestive enzymes to break down large molecules into smaller ones that can be reused by cells. GlcNAc-1-phosphotransferase is involved in the process of attaching a molecule called mannose‑6‑phosphate (M6P) to specific digestive enzymes. Just as luggage is tagged at the airport to direct it to the correct destination, enzymes are often “tagged” after they are made so they get to where they are needed in the cell. M6P acts as a tag that indicates a digestive enzyme should be transported to the lysosome.

Mutations in the GNPTAB gene that cause mucolipidosis III alpha/beta result in reduced activity of GlcNAc-1-phosphotransferase. These mutations disrupt the tagging of digestive enzymes with M6P, which prevents many enzymes from reaching the lysosomes. Digestive enzymes that do not receive the M6P tag end up outside the cell, where they have increased activity. The shortage of digestive enzymes within lysosomes causes large molecules to accumulate there. Conditions that cause molecules to build up inside lysosomes, including mucolipidosis III alpha/beta, are called lysosomal storage disorders. The signs and symptoms of mucolipidosis III alpha/beta are most likely due to the shortage of digestive enzymes inside lysosomes and the effects these enzymes have outside the cell.

Mutations in the GNPTAB gene can also cause a similar but more severe disorder called mucolipidosis II alpha/beta. These mutations completely eliminate the function of GlcNAc-1-phosphotransferase. Mucolipidosis III alpha/beta and mucolipidosis II alpha/beta represent two ends of a spectrum of disease severity.

Learn more about the gene associated with Mucolipidosis III alpha/beta

  • GNPTAB

Inheritance

This condition is inherited in an autosomal recessive manner, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Other Names for This Condition

  • ML III
  • ML IIIA
  • Mucolipidosis III
  • Mucolipidosis III, variant
  • Mucolipidosis IIIA
  • Pseudo‑Hurler polydystrophy

Additional Information & Resources

Genetic Testing Information

  • Genetic Testing Registry: Pseudo‑Hurler polydystrophy

Patient Support and Advocacy Resources

  • National Organization for Rare Disorders (NORD)

Clinical Trials

  • ClinicalTrials.gov

Catalog of Genes and Diseases from OMIM

  • MUCOLIPIDOSIS III ALPHA/BETA

Scientific Articles on PubMed

  • Bargal R, Zeigler M, Abu‑Libdeh B, Zuri V, Mandel H, Ben Neriah Z, Stewart F, Elcioglu N, Hindi T, Le Merrer M, Bach G, Raas‑Rothschild A. When Mucolipidosis III meets Mucolipidosis II: GNPTA gene mutations in 24 patients. Mol Genet Metab. 2006 Aug;88(4):359‑63. doi: 10.1016/j.ymgme.2006.03.003. Epub 2006 Apr 21. Citation on PubMed
  • Cathey SS, Kudo M, Tiede S, Raas‑Rothschild A, Braulke T, Beck M, Taylor HA, Canfield WM, Leroy JG, Neufeld EF, McKusick VA. Molecular order in mucolipidosis II and III nomenclature. Am J Med Genet A. 2008 Feb 15;146A(4):512‑3. doi: 10.1002/ajmg.a.32193. No abstract available. Citation on PubMed
  • Cathey SS, Leroy JG, Wood T, Eaves K, Simensen RJ, Kudo M, Stevenson RE, Friez MJ. Phenotype and genotype in mucolipidoses II and III alpha/beta: a study of 61 probands. J Med Genet. 2010 Jan;47(1):38‑48. doi: 10.1136/jmg.2009.067736. Epub 2009 Jul 16. Citation on PubMed or Free article on PubMed Central
  • Kudo M, Brem MS, Canfield WM. Mucolipidosis II (I‑cell disease) and mucolipidosis IIIA (classical pseudo‑hurler polydystrophy) are caused by mutations in the GlcNAc‑phosphotransferase alpha / beta‑subunits precursor gene. Am J Hum Genet. 2006 Mar;78(3):451‑63. doi: 10.1086/500849. Epub 2006 Jan 24. Citation on PubMed or Free article on PubMed Central
  • Otomo T, Muramatsu T, Yorifuji T, Okuyama T, Nakabayashi H, Fukao T, Ohura T, Yoshino M, Tanaka A, Okamoto N, Inui K, Ozono K, Sakai N. Mucolipidosis II and III alpha/beta: mutation analysis of 40 Japanese patients showed genotype‑phenotype correlation. J Hum Genet. 2009 Mar;54(3):145‑51. doi: 10.1038/jhg.2009.3. Epub 2009 Feb 6. Citation on PubMed
  • Steet RA, Hullin R, Kudo M, Martinelli M, Bosshard NU, Schaffner T, Kornfeld S, Steinmann B. A splicing mutation in the alpha/beta GlcNAc‑1‑phosphotransferase gene results in an adult onset form of mucolipidosis III associated with sensory neuropathy and cardiomyopathy. Am J Med Genet A. 2005 Feb 1;132A(4):369‑75. doi: 10.1002/ajmg.a.30498. Citation on PubMed
  • Tiede S, Muschol N, Reutter G, Cantz M, Ullrich K, Braulke T. Missense mutations in N‑acetylglucosamine‑1‑phosphotransferase alpha/beta subunit gene in a patient with mucolipidosis III and a mild clinical phenotype. Am J Med Genet A. 2005 Sep 1;137A(3):235‑40. doi: 10.1002/ajmg.a.30868. Citation on PubMed
  • Tylki‑Szymanska A, Czartoryska B, Groener JE, Lugowska A. Clinical variability in mucolipidosis III (pseudo‑Hurler polydystrophy). Am J Med Genet. 2002 Mar 15;108(3):214‑8. doi: 10.1002/ajmg.10224. Citation on PubMed
  • van Meel E, Qian Y, Kornfeld SA. Mislocalization of phosphotransferase as a cause of mucolipidosis III alpha/beta. Proc Natl Acad Sci U S A. 2014 Mar 4;111(9):3532‑7. doi: 10.1073/pnas.1401417111. Epub 2014 Feb 18. Citation on PubMed or Free article on PubMed Central

MedlinePlus Links

  • Cloudy cornea
  • Genetics
  • Heart Valves (Image)

Understanding Genetics

  • What is the prognosis of a genetic condition?
  • How can gene variants affect health and development?
  • What does it mean if a disorder seems to run in my family?
  • What are the different ways a genetic condition can be inherited?
  • How are genetic conditions treated or managed?

Frequently Asked Questions

Because individuals with this condition often have stiff joints and low bone mineral density, high-impact activities like running or jumping should be avoided to prevent fractures. Instead, low-impact exercises such as swimming, water aerobics, or gentle stationary cycling are generally recommended to maintain muscle strength and joint flexibility without placing excessive stress on the bones. Physical therapists can design specific stretching and strengthening programs tailored to the individual's current range of motion and pain levels, which should be performed consistently to slow the progression of joint contractures.
multidisciplinary care plan is essential for managing the progressive nature of the disease. This typically includes regular orthopedic evaluations to monitor bone density and joint health, often involving DEXA scans and x-rays. Cardiac monitoring is necessary to track valve abnormalities, which may require echocardiograms every few years. Ophthalmologic exams are needed to check for corneal clouding and vision changes. Additionally, a neurologist or developmental specialist may be involved to manage any cognitive or learning challenges, while a dietitian ensures adequate nutrition to support bone health and overall energy levels.
Mucolipidosis III alpha/beta follows an autosomal recessive inheritance pattern, meaning a person must inherit two mutated copies of the GNPTAB gene, one from each parent, to develop the condition. Parents who are carriers typically do not show symptoms but have a 25 percent chance with each pregnancy of having a child with the disorder, a 50 percent chance of having a child who is a carrier, and a 25 percent chance of having a child with neither the condition nor the carrier status. Genetic counseling is recommended for families with a history of the disease to assess risks and discuss testing options.
Preventing infections involves a combination of hygiene practices and medical monitoring. Regular hand washing and avoiding close contact with individuals who are sick can reduce the risk of respiratory viruses. For ear infections, which are common due to anatomical changes, prompt treatment by an ENT specialist is crucial to prevent hearing loss. Keeping vaccinations up to date, particularly for influenza and pneumonia, is also important. If respiratory infections become recurrent or severe, a pulmonologist may recommend specific breathing exercises or monitoring for underlying structural issues that complicate lung function.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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