A 6-year-old girl diagnosed with mevalonate kinase deficiency who had hydrops fetalis and neonatal-onset cholestasis.

We experienced a 6-year-old girl diagnosed with mevalonate kinase deficiency (MKD) who had cholestasis, anemia, and elevated inflammatory markers in neonatal period. She was admitted to our hospital because of fever and elevated inflammatory markers at 5 years 11months of age. Without using antibiotics, the fever and the inflammatory markers were spontaneously resolved. MKD was suspected from elevated serum IgD level and the recurrent febrile attacks. The genetic test revealed heterozygous mutation of p.Leu51Phe known as causative gene of MKD and p.Met 282Thr which is the novel mutation. In addition, urinary mevalonate levels increased both in afebrile and febrile periods, and mevalonate kinase activity level was very low. Prednisolone was administered on each attack, and her febrile attack has been controlled well since she was diagnosed with MKD. Fetal edema, cholestasis, anemia, elevation of inflammatory markers in her neonatal period are considered to be complications of MKD. Recurrent fever attacks compromise quality of life in patients with MKD. Children with unexplained cholestasis and anemia in neonatal period, or recurrent fever attacks with elevated inflammatory markers should be examined for MKD.