I-Cell Disease (Mucolipidosis Type II) 

  • Author: Karl S Roth, MD; Chief Editor: Bruce Buehler, MD   more...
 
Updated: Sep 1, 2009
 

Background

I-cell disease is an inherited lysosomal storage disorder.[1] It first was described in 1967 by Leroy and DeMars when they reported a patient with clinical and radiographic features similar to those of Hurler syndrome (mucopolysaccharidoses 1H [MPS 1H]) but with an earlier onset of symptoms and no evidence of mucopolysacchariduria.[2] One unique feature of this disease was the presence of phase-dense intracytoplasmic inclusions in the fibroblasts of patients. These cells were termed inclusion cells, or I-cells; thus, the disease was designated I-cell disease. Spranger and Wiedermann subsequently classified this disease as mucolipidosis type II (ML II) because it had clinical characteristics that included mucopolysaccharidoses and sphingolipidoses.[3]

Profile view of 3-year-old with I-cell disease. GrProfile view of 3-year-old with I-cell disease. Growth ceased more than one year earlier. Note small orbits, proptotic eyes, full and prominent mouth caused by gingival hypertrophy, short and broad hands, stiffening of small hand joints, prominent abdomen with umbilical hernia, and limited extension of the hips and knees.
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Pathophysiology

Early enzymologic studies showed that cultured fibroblasts from patients with I-cell disease were deficient in numerous lysosomal enzymes. Furthermore, these enzymes were found to be present in excess in tissue culture media and in extracellular fluids, such as serum and urine. I-cell disease fibroblasts were subsequently discovered to be able to internalize and use lysosomal enzymes produced by normal cells, whereas normal or other lysosomal disease fibroblasts were incapable of internalizing lysosomal enzymes secreted by the I-cell disease fibroblasts.

The above findings suggested that a biochemical marker signal may be required for proper trafficking of the lysosomal enzyme, from the site of its production in the endoplasmic reticulum to the lysosome itself. This marker was later identified as a mannose-6-phosphate residue on the lysosomal enzyme that interacts with a specific receptor on the lysosomal membrane, which then triggers endocytosis into the lysosome. The biochemical defect in I-cell disease involves the first step in the addition of the mannose-6-phosphate moiety. The enzyme that catalyzes this reaction is uridine diphospho (UDP)-N -acetylglucosamine: N -acetylglucosaminyl-1-phosphotransferase.

As in many of the lysosomal storage diseases, the functional deficiency of lysosomal enzymes results in abnormal cell architecture. In I-cell disease, the characteristic finding is abnormal vacuolization or inclusions that appear in the cytoplasm. These are observed in cells of mesenchymal origin, especially fibroblasts. The most severely affected system is the skeletal system, in which trabeculation of bone and cartilage structures are abnormal. Muscular tissue, including cardiac muscle, is relatively spared; however, significant vacuolization is present in the art’s connective tissue cells of the heart valves. This leads to thickening of the valves, which results in clinically significant valvular disease. Other sites of abnormal cell vacuolization include the renal glomerular podocytes and in the fibroblasts of the liver’s periportal spaces. Hepatocytes and Kupffer cells are not affected.

Interestingly, although psychomotor retardation is a major manifestation of this disease, the pathologic findings in CNS tissue are not as striking as in other organs. Among reported findings is the presence of lamellar bodies in spinal ganglia neurons and in anterior horn cells; however, these findings are not consistent in all patients. Vacuolization of peripheral Schwann cells is minimal but not enough to impair normal myelination.

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Epidemiology

Frequency

International

I-cell disease is a rare disorder that has no ethnic predilection. Very little population data are available, but a recent study from the Netherlands reported a frequency of approximately 1 in 640,000 live births.[4]

Mortality/Morbidity

Death from pneumonia or congestive heart failure usually occurs within the first decade of life.

Race

I-cell disease has no racial predilection.

Sex

I-cell disease is inherited as an autosomal-recessive trait. Both sexes are equally affected.

Age

Clinical manifestations can be present at birth or may present in the first few months of life.

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Contributor Information and Disclosures
Author

Karl S Roth, MD  Professor and Chair, Department of Pediatrics, Creighton University School of Medicine

Karl S Roth, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American College of Nutrition, American Pediatric Society, American Society for Clinical Nutrition, American Society of Nephrology, Association of American Medical Colleges, Medical Society of Virginia, New York Academy of Sciences, Sigma Xi, Society for Pediatric Research, and Southern Society for Pediatric Research

Disclosure: MDS Pharma Salary Employment

Coauthor(s)

William B Rizzo, MD  Professor, Department of Pediatrics, University of Nebraska Medical Center

William B Rizzo, MD is a member of the following medical societies: American Society of Human Genetics and Society for Inherited Metabolic Disorders

Disclosure: Nothing to disclose.

Margaret M McGovern, MD, PhD  Professor and Chair of Pediatrics, Stony Brook University, New York

Margaret M McGovern, MD, PhD is a member of the following medical societies: American Academy of Pediatrics and American Society of Human Genetics

Disclosure: Genzyme Grant/research funds PI

Specialty Editor Board

Edward Kaye, MD  Vice President of Clinical Research, Genzyme Corporation

Edward Kaye, MD is a member of the following medical societies: American Academy of Neurology, American Society of Gene Therapy, American Society of Human Genetics, Child Neurology Society, and Society for Inherited Metabolic Disorders

Disclosure: Genzyme Corporation Salary Management position

Mary L Windle, PharmD  Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine

Disclosure: Pfizer Inc Stock Investment from financial planner; Avanir Pharma Stock Investment from financial planner ; WebMD Salary and stock Employment and investment from financial planner

Margaret M McGovern, MD, PhD  Professor and Chair of Pediatrics, Stony Brook University, New York

Margaret M McGovern, MD, PhD is a member of the following medical societies: American Academy of Pediatrics and American Society of Human Genetics

Disclosure: Genzyme Grant/research funds PI

Paul D Petry, DO, FACOP, FAAP  Consulting Staff, Freeman Pediatric Care, Freeman Health System

Paul D Petry, DO, FACOP, FAAP is a member of the following medical societies: American Academy of Osteopathy, American Academy of Pediatrics, American College of Osteopathic Pediatricians, and American Osteopathic Association

Disclosure: Nothing to disclose.

Chief Editor

Bruce Buehler, MD  Professor, Department of Pediatrics, Pathology and Microbiology, Executive Director, Hattie B Munroe Center for Human Genetics, University of Nebraska Medical Center

Bruce Buehler, MD is a member of the following medical societies: American Academy for Cerebral Palsy and Developmental Medicine, American Academy of Pediatrics, American Association on Mental Retardation, American College of Medical Genetics, American College of Physician Executives, American Medical Association, and Nebraska Medical Association

Disclosure: Nothing to disclose.

References
  1. Dierks T, Schlotawa L, Frese MA, Radhakrishnan K, von Figura K, Schmidt B. Molecular basis of multiple sulfatase deficiency, mucolipidosis II/III and Niemann-Pick C1 disease - Lysosomal storage disorders caused by defects of non-lysosomal proteins. Biochim Biophys Acta. Apr 2009;1793(4):710-25. [Medline].

  2. Leroy JG, DeMars RI, Opitz JM. I-cell disease. Birth Defects Orig Artic Ser. 1969;4:174-85.

  3. Spranger JW, Wiedemann HR. The genetic mucolipidoses. Diagnosis and differential diagnosis. Humangenetik. 1970;9(2):113-39. [Medline].

  4. Poorthuis BJ, Wevers RA, Kleijer WJ, et al. The frequency of lysosomal storage diseases in The Netherlands. Hum Genet. Jul-Aug 1999;105(1-2):151-6. [Medline].

  5. Krivan G, Timar L, Goda V, et al. Bone marrow transplantation in non-malignant disorders. Bone Marrow Transplant. Dec 1998;22 Suppl 4:S80-3. [Medline].

  6. Bocca G, Monnens LA. Defective proximal tubular function in a patient with I-cell disease. Pediatr Nephrol. Aug 2003;18(8):830-2. [Medline].

  7. Breningstall GN, Tubman DE. Magnetic resonance imaging in a patient with I-cell disease. Clin Neurol Neurosurg. May 1994;96(2):161-3. [Medline].

  8. Goodman ML, Pang D. Spinal cord injury in I-cell disease. Pediatr Neurosci. 1988;14(6):315-8. [Medline].

  9. Gopaul KP, Crook MA. The inborn errors of sialic acid metabolism and their laboratory investigation. Clin Lab. 2006;52(3-4):155-69. [Medline].

  10. Kawashima I, Ohsawa M, Fukushige et al. Cytochemical analysis of storage materials in cultured skin fibroblasts from patients with I-cell disease. Clin Chim Acta. Mar 2007;378(1-2):142-6. [Medline].

  11. Kornfeld S, Sly WS. I-cell disease and pseudo-Hurler polydystrophy: disorders of lysosomal enzyme phosphorylation and localization. Metab Mol Bases Inherited Dis. 2001;3:3469-82.

  12. 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. Mar 2006;78(3):451-63. [Medline].

  13. Leroy JG, Martin JJ. Mucolipidosis II (I-cell disease): present status of knowledge. Birth Defects Orig Artic Ser. 1975;DA - 19760301(6):283-93. [Medline].

  14. Leroy JG, Spranger JW, Feingold M, Opitz JM, Crocker AC. I-cell disease: a clinical picture. J Pediatr. Sep 1971;79(3):360-5. [Medline].

  15. Tiede S, Storch S, Lubke T, et al. Mucolipidosis II is caused by mutations in GNPTA encoding the alpha/beta GlcNAc-1-phosphotransferase. Nat Med. Oct 2005;11(10):1109-12. [Medline].

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Profile view of 3-year-old with I-cell disease. Growth ceased more than one year earlier. Note small orbits, proptotic eyes, full and prominent mouth caused by gingival hypertrophy, short and broad hands, stiffening of small hand joints, prominent abdomen with umbilical hernia, and limited extension of the hips and knees.
 
 
 
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