A new lysosomal storage disorder resembling Morquio syndrome in sibs

We report two male sibs, born from unrelated French Caribbean parents, presenting with an unclassifiable storage disorder. Pregnancy and delivery were uneventful. Stunted growth was noted during the first year of life. Both children have short stature (below - 4SD) with short trunk, barrel chest, micromelia with rhizomelic shortening, severe kyphoscoliosis, pectus carinatum, short hands and feet with metatarsus adductus, and excessive joint laxity of the small joints. Learning difficulties with borderline intelligence quotient (IQ) were noted in one of them. They had no hepatomegaly, no splenomegaly, and no dysmorphism. Skeletal X-rays survey demonstrated generalized platyspondyly with tongue-like deformity of the anterior part of the vertebral bodies, hypoplasia of the odontoid process, generalized epiphyseal dysplasia and abnormally shaped metaphyses. The acetabular roofs had a trident aspect. Ophthalmologic and cardiac examinations were normal. Spine deformity required surgical correction in one of the patient at age 4 years. Lysosomal enzymes assays including N-acetylgalactosamine-6-sulfate sulfatase and β-galactosidase were normal, excluding mucopolysaccharidoses type IV A and IV B (Morquio syndrome), respectively. Qualitative analysis found traces of dermatan and chondroitin-sulfates in urine, but quantitative glycosaminoglycan excretion fell within normal limits. They were no vacuolated lymphocytes. Abnormal coarse inclusions were present in eosinophils. Mild Alder anomaly was observed in polymorphonuclears. Granulations were discretely metachromatic with toluidine blue. Those morphological anomalies are in favor of a lysosomal storage disease. No inclusions were found in skin fibroblasts. We hypothesize that these two boys have a distinct autosomal recessive or X-linked lysosomal storage disorder of unknown origin that shares clinical and radiological features with Morquio disease.