Mucolipidosis II Alpha/Beta

Alternative Names

  • Mucolipidosis II
  • ML II Alpha/Beta
  • ML II
  • I-Cell Disease
  • ICD
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WHO-ICD-10 version:2010

Endocrine, nutritional and metabolic diseases

Metabolic disorders

OMIM Number

252500

Mode of Inheritance

Autosomal recessive

Gene Map Locus

12q23.3

Description

Mucolipidosis II (MLII) is a rare lysosomal storage disease due to the deficiency of N-acetylglucosaminyl 1-phosphotransferase which results in the defective lysosomal targeting of several lysosomal enzymes. The multiple enzyme deficiencies cause accumulation of fatty substances (mucolipids) and complex carbohydrates (mucopolysaccharides) within the cells of many tissues of the body leading to abnormal cell architecture. However, the most affected system is the skeletal system that has abnormal trabeculation of bone and cartilage. The disease onset is during the first months of life, or sometimes even during the intrauterine period. The main features of MLII are hypertrophic gingiva and enlarged tongue, coarse facies, hirsutism, hernias, cutaneous infiltration, limited joint mobility, dysostosis multiplex, hepatosplenomegaly, corneal opacities, deafness, mental and motor retardation, and dwarfism. Mostly, the patients die in the childhood due to cardiorespiratory complications. The lysosomal enzyme activities show an unusual increase in the serum and urine, while they are decreased in cultured fibroblasts. The patients' fibroblasts have phase-dense intracytoplasmic inclusions, therefore, these cells are termed inclusion cells (I-cells) and MLII is also known as I-cell disease.

Mucolipidosis II (MLII) is caused by a mutation in the N-acetylglucosamine-1-phosphate transferase, alpha and beta subunits (GNPTAB) gene that leads to a deficiency in the enzyme N-acetylglucosaminyl 1-phosphotransferase. The normal enzyme is composed of three polypeptide subunits (alpha, beta, and gamma) which are encoded by two different genes. In MLII, the alpha and beta subunits are altered due to mutations in the GNPTAB gene.

Epidemiology in the Arab World

View Map
Subject IDCountrySexFamily HistoryParental ConsanguinityHPO TermsVariantZygosityMode of InheritanceReferenceRemarks
252500.1United Arab EmiratesUnknownNM_024312.4:c.3503_3504delHomozygousAutosomal, RecessiveAli et al. 2011
252500.2United Arab EmiratesNM_024312.4:c.3503_3504delHomozygousAutosomal, RecessiveAl-Jasmi et al. 2013 Infantile onset
252500.3Saudi ArabiaMaleYesYes Skeletal dysplasia; Proptosis; Short nec...NM_024312.4:c.3503_3504delHomozygousAutosomal, RecessiveMaddirevula et al. 2018
252500.4Saudi ArabiaFemaleYes Recurrent fractures; Neonatal hypotonia;...NM_024312.5:c.3653delHomozygousAutosomal, RecessiveMaddirevula et al. 2018

Other Reports

Palestine

Benson et al. (1988) reported a Palestinian patient in Sharjah in the United Arab Emirates with I-cell disease. Because of the presence of another Arab patient with I-cell disease, Benson et al. (1988) concluded that there was an ethnic predisposition to I-cell disease amongst Arabs.

Saudi Arabia

Benson et al. (1988) reported a Saudi patient with I-cell disease [Benson PF, Fahmy NA, Fenson AH. Is there an ethnic Arab predisposition to mucolipidosis type II? Saudi Med J. 1988; 4:381-8].

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