Patient description: A 3-day-old Asian female infant presents with jaundice that started a day ago. She was born at 38w3d of gestation, after an uncomplicated pregnancy. The family history is unremarkable. The baby is breastfed. Vital signs are reported as: axillary temperature: 36.3°C, heart rate: 154 beats/min, respiratory rate: 37 breaths/min, and blood pressure: 65/33 mm Hg. Her weight is 3.2 kg, length is 53 cm, and head circumference 36 cm. Her sclera are yellow and her body is icteric. No murmurs or any other abnormalities are detected in the heart and lung auscultation. Her liver and spleen are normal on palpation. Laboratory results are as follows: Serum total bilirubin: 21.02 mg/dL Direct bilirubin of 2.04 mg/dL AST: 37 U/L ALT: 20 U/L GGT: 745 U/L Alkaline phosphatase: 531 U/L Creatinine: 0.3 mg/dL Urea: 29 mg/dL Na: 147 mEq/L K: 4.5 mEq/L CRP: 3 mg/L Complete blood cell count within the normal range. She is diagnosed with uncomplicated neonatal jaundice that may require phototherapy.

Clinical trial eligibility criteria: eligible ages (years): 18.0-45.0,  Healthy Volunteers Normal Body Mass index (BMI) and weight: BMI[= weight kg/(height m)^2] > 19 kg/m^2 and ≤ 24 kg/m^2, the weight is no less than 50 kg for male and 45 kg for female at screening Female subject must either: Be of non-childbearing potential, postmenopausal (defined as at least 1 year without any menses) prior to screening, or documented surgically sterile. Or, if of childbearing potential: agree not to try to become pregnant during the study and for 60 days after the final study drug administration, must have a negative pregnancy at Screening and Day -1, and if heterosexually active, agree to consistently use 1 form of highly effective birth control starting at Screening and throughout the study period, and for 60 days after the final study drug administration Female subject must agree not to breastfeed starting at Screening and throughout the study period, and for 60 days after the final study drug administration Female subject must not donate ova starting at Screening and throughout the study period, and for 60 days after the final study drug administration Male subject and female spouse/partners who are of childbearing potential must be using 1 form of highly effective birth control starting at Screening and throughout the study period, and for 90 days after the final study drug administration Male subject must not donate sperm starting at Screening and throughout the study period, and for 90 days after the final study drug administration Subject agrees not to participate in another interventional study while participating in the present study, defined as signing the informed consent form until completion of the last study visit  Female subject who has been pregnant within 6 months prior to screening or breast feeding within 3 months prior to screening Subject has a known or suspected hypersensitivity to ASP015K, or any components of the formulation used Subject has any of the liver chemistry tests (aspartate aminotransferase [AST], alanine aminotransferase [ALT], alkaline phosphatase [ALP], gamma-glutamyl transferase [GGT] and total bilirubin [TBL]) above the upper limit of normal on Day -1. In such a case, the assessment may be repeated once Subjects who meet any of the following criterion for laboratory tests on Day -1. Normal ranges of each test specified at the study site or test/assay organization will be used as the normal ranges in this study. In such a case, the assessment may be repeated once Hematology: a deviation of +20% from the upper limit or -20% from the lower limit of the normal range, and clinically significant Blood biochemistry: a deviation from the normal range regarding serum creatinine, serum electrolytes (Na, K, and Cl), or fasting blood glucose; a deviation of +20% from the upper limit or -20% from the lower limit of the normal range regarding laboratory test items other than above, and clinically significant. However, the lower limit of the normal range will not be established for lactate dehydrogenase (LD), creatinine kinase (CK), total cholesterol, triglyceride, urea, serum creatinine, and uric acid, whose deviation from the lower limit is considered not clinically significant Urinalysis: a deviation from the normal range of each urinalysis test item Subject has any clinically significant history of allergic conditions (including drug allergies, asthma, eczema, or anaphylactic reactions, but excluding untreated, asymptomatic, seasonal allergies at time of dosing) Subject has any history or evidence of any clinically significant cardiovascular, gastrointestinal endocrinologic, hematologic, hepatic, immunologic, metabolic, urologic, respiratory,pulmonary, neurologic, cerebrovascular, lymphatic, dermatologic, psychiatric, renal, and/or other major disease or malignancy Subject has/had febrile illness or symptomatic, viral, bacterial (including upper respiratory infection), or fungal (noncutaneous) infection within 1 week prior to Day -1