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Mucolipidosis II.


GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2016.
2008 Aug 26 [updated 2012 May 10].



Mucolipidosis II (ML II, I-cell disease) is a slowly progressive inborn error of metabolism with clinical onset at birth and fatal outcome most often in early childhood. Postnatal growth is limited and often ceases in the second year of life; contractures develop in all large joints. The skin is thickened, facial features are coarse, and gingiva are hypertrophic. Orthopedic abnormalities present at birth may include thoracic deformity, kyphosis, clubfeet, deformed long bones, and/or dislocation of the hip(s). Already in infancy skeletal radiographs reveal dysostosis multiplex. All children appear to have cardiac involvement, most commonly thickening and insufficiency of the mitral valve and, less frequently, the aortic valve. Progressive mucosal thickening narrows the airways and gradual stiffening of the thoracic cage contributes to respiratory insufficiency, the most common cause of death.


Activity of nearly all lysosomal hydrolases is five- to 20-fold higher in plasma and other body fluids than in normal controls because of improper targeting of lysosomal acid hydrolases to lysosomes in ML II. Urinary excretion of oligosaccharides (OSs) is excessive. GNPTAB is the only gene in which pathogenic variants are known to cause ML II. Bidirectional sequencing of the entire GNPTAB coding region detects two pathogenic variants in more than 95% of persons with ML II.


Treatment of manifestations: “Low-impact” therapies to avoid joint and tendon strain, including aqua therapy, are usually well tolerated; cognitive stimulation through interactive programs; gingivectomy as needed for oral health; myringotomy tube placement as needed for recurrent ear infections. Prevention of secondary complications: Because of concerns about airway management, surgical intervention should be avoided as much as possible and undertaken only in tertiary care settings. Surveillance: Outpatient follow-up visits approximately every three months for infants and toddlers; outpatient visits approximately every six months for older children until cardiac and respiratory monitoring need to be more frequent.


ML II is inherited in an autosomal recessive manner. At conception, each sib of an affected person has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk relatives and prenatal testing for pregnancies at increased risk are possible if the pathogenic variants in the family are known.

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