To determine if a one-time oral administration of ergocalciferol results in a decline in plasma mucin-1 levels in healthy individuals and individuals with ADTKD-MUC1.

This is a pilot, open-labelled, to determine if oral administration of a single dose of ergocalciferol lowers plasma mucin-1 levels. The study population will include 40 healthy individuals and 40 individuals with ADTKD-MUC1.

The study consists of an initial screening, signing of consent of interested individuals, performance of pregnancy test in women of child-bearing age and screening labs, and administration of 200,000 units of ergocalciferol on Day 0 (On Study). Laboratory studies will be performed at baseline, on Days 3, 7, and 10.

Inclusion Criteria:

• Age > 18 years and <65 years
• Females must be non-pregnant, non-lactating and fulfilling one of the following: a. Post menopausal defined as amenorrhea for at least 12 months following cessation of all exogenous hormonal treatments. b. Status post irreversible surgical sterilization by hysterectomy, bilateral oophorectomy or bilateral salpingectomy but not tubal ligation. c.

Use of acceptable contraceptive method: IUD with spermicide, a female condom with spermicide, contraceptive sponge with spermicide, an intravaginal system(e.g., NuvaRing®), a diaphragm with spermicide, a cervical cap with spermicide, or oral, implantable, transdermal, or injectable contraceptives, sexual abstinence, or a sterile sexual partner.

• Males must agree to avoid fathering a child (or donating sperm), and therefore be either sterile or agree to use, from the time of enrollment until 45 days after end of study, one of the following approved methods of contraception: a male condom with spermicide, a sterile sexual partner, use by female sexual partner of an IUD with spermicide, a female condom with spermicide, contraceptive sponge with spermicide, an intravaginal system (e.g.,NuvaRing®), a diaphragm with spermicide, a cervical cap with spermicide, or oral, implantable, transdermal, or injectable contraceptives.
• No serious health conditions except for estimated glomerular filtration rate <30 ml/min/1.73 m2 (according to the modified MDRD formula) in participants with ADTKD- MUC1.
• Prior established genetic diagnosis of ADTKD-MUC1 in participants recruited with ADTKD-MUC1.
• Able to understand and comply with requirements of the entire study and to communicate with the study team.
• Living in close enough proximity to a local laboratory to obtain labwork for the study.
• Written informed consent using a document that has been approved by the Institutional Review Board.
• The participant has not taken ergocalciferol in the month prior to study initiation. If receiving cholecalciferol, the dose is < 1000/day and has been stopped one month prior to Day 0 (On Study).
• Participants agree NOT to take ergocalciferol or cholecalciferol (except for<500 IU that contained in a daily multi-vitamin) for six months after receiving the one-time dose of ergocalciferol.

Exclusion Criteria:

• Major systemic illness other than chronic kidney disease in individuals with ADTKD- MUC1.
• A history of granulomatous disorders (sarcoidosis, tuberculosis), hyperparathyroidism, or other disorders of calcium metabolism.
• A history of nephrolithiasis.
• A history of osteoporosis or osteopenia.
• A fracture or a fall that did not occur during exercise within the last six months.
• Intolerance or known allergic reaction to ergocalciferol.
• 25 hydroxy Vitamin D level > upper limit of normal.
• Lactating.
• Liver disease.
• Receiving glucocorticoids.