Mucolipidosis: aspectos clínicos y genéticos

Abstract

The concept of the mucolipidoses developed as the result of encounters with patients whose clinical appearance suggested a mucopolysaccharidosis, i.e. coarse facies, short stature, skeletal dysplasia, joint contractures and lysosomal accumulations but did not have an excess of mucopolysaccharides in their urine. This clinical phenotype embraces the early onset forms of sialidosis (mucolipidosis I), as well as I-cell disease (mucolipidosis II) and pseudoHurler polydystrophy (mucolipidosis III). Two disorders that were later added to the mucolipidoses, the Cherry-red Spot Myoclonus Epilepsy Syndrome (sialidosis type I) and mucolipidosis IV differ in that the facial appearance is normal and they do no have skeletal dysmorphism. Enzyme deficiencies have been identified in mucolipidosis I, II and III. The basic molecular cause of mucolipidosis IV is not known but linkage analysis is underway to identify the chromosomal map position of the defective gene. Precise diagnosis of these autosomal recessively inherited diseases depends upon radiographic studies for skeletal dysplasias, analyses of urine for sialyloligosaccharides, morphologic studies of bone marrow and skin biopsy specimens and enzymatic determinations of sialidase and UDP-N-acetylglucosamine: lysosomal enzyme N-acetylglucosamine-1-phosphotransferase. Case descriptions from the author's experience are presented to illustrate the use of a decision tree employing these diagnostic modalities. The existence of naturally-occurring animal models for sialidase deficiency (SM/J mouse) and the phosphotransferase deficiency (mucolipidosis III cat) provide opportunities to develop new therapeutic approaches.