Mucolipidosis IV: novel mutation and diverse ultrastructural spectrum in the skin

Mucolipidosis IV, a severe neurologic and ophthalmologic progressive disorder has a clinical range of onset between early childhood and adolescence entailing clinically severe, moderate, and mild forms, all of them majorly affecting Ashkenazi Jewish patients in an autosomal-recessive fashion owing to mutations in the MCOLN1 gene which encodes a transmembrane protein called mucolipin 1. We report on one of two affected siblings, the older brother having died of ML IV at the age of 33 years, the younger recently at the age of 37 years. Biopsied skin disclosed several types of lysosomal residual bodies, membrane-bound vacuoles, avacuolar lamellar bodies resembling membraneous cytoplasmic bodies, and a diverse spectrum of lipopigments which include curvilinear and fingerprint profiles. Contrary to earlier reports, disease-specific lysosomal residual bodies could not be identified in circulating lymphocytes of our patient. Mutation analysis revealed a homozygous novel mutation of a 34 bp deletion and 3 bp insertion in exon 2 of the MCOLN1 gene, perhaps the reason for this unusual clinical and morphological phenotype.