A case of mucolipidosis II presenting with prenatal skeletal dysplasia and severe secondary hyperparathyroidism at birth

Heo, Ju Sun; Choi, Ka Young; Sohn, Se Hyoung; Kim, Curie; Kim, Yoon Joo; Shin, Seung Han; Lee, Jae Myung; Lee, Juyoung; Sohn, Jin A; Lim, Byung Chan; Lee, Jin A; Choi, Chang Won; Kim, Ee-Kyung; Kim, Han-Suk; Kim, Beyong Il; Choi, Jung-Hwan

Several reports have described cases of ML II that expressed skeletal dysplasia prenatally 28, 29) . In Lachman's study 29) , the most common disorders associated with fetal skeletal dysplasia were osteogenesis imperfect (18%), thanatophoric dysplasia (14%), campomelic dysplasia (6%), and achondrogenesis type II (5%). In that report, 8 patients were diagnosed with ML II. Their sonographic findings showed short long bones, and 4 cases were detected during the second trimester. In the present case, prenatal ultrasonographic findings included rhizomelia in the upper extremities and micromelia in the lower extremities. Our patient exhibited severe skeletal changes from multiple frac tures, diffuse diaphyseal cloaking in the long bones, marked osteopenia, underossification of the calvarium, and resorption of the mandible with loss of the lamina dura. The distal metaphyses of long tubular bones showed irregular demineralization, which is seen in rickets. These signs suggest the presence of hyperparathyroidism, which was confirmed by the high levels of ALP and PTH. However, in contrast to neonatal severe primary hyperparathyroidism, her total Ca level was normal. These observations are consistent with severe secondary neonatal hyperparathyroidism. The etiology of severe secondary hyperparathyroidism in fetuses and newborns with ML II is uncertain. However, it is speculated that the enzyme-targeting defect in ML II involves trophoblasts and syncytiotrophoblasts in the placenta; this interferes with transplacental Ca transport and leads to Ca starvation of the fetus and activation of the parathyroid response to maintain extracellular Ca 18) . This hypothesis is supported by the findings of foamy vacuolar changes in trophoblasts and syncytiotrophoblasts in the present case.