‣ Study participants must meet all of the following inclusion criteria:

• Caregiver's written or electronic informed consent after the nature of the study has been explained, and prior to any research-related procedures, per International Conference on Harmonisation (ICH) Good Clinical Practice (GCP)

• Study participant's assent in accordance with local regulations

• A confirmed postnatal molecular genetic diagnosis of ENPP1 Deficiency with biallelic mutations (ie, homozygous or compound heterozygous) performed by a College of American Pathologists/Clinical Laboratory Improvement Amendments (CAP/CLIA) certified laboratory or regional equivalent

• Males and females ≥1 year and \<13 years of age at Study Day 1

• Open growth plates of the distal femur and proximal tibia in both legs

• Plasma PPi concentration of \<1400 nM at Screening

• 25-hydroxyvitamin D (25\[OH\]D) levels of ≥12 ng/mL at Screening

• Radiographic evidence of skeletal abnormalities based on an RSS ≥2

• Female participants of childbearing potential must have a negative serum pregnancy test at Screening and must not be breastfeeding

⁃ Study participants of childbearing potential who are sexually active must agree to use a highly effective form of contraception in accordance with Clinical Trials Facilitation and Coordination Group (CTFG) guidance and local guidelines for the duration of the study

⁃ In the opinion of the Investigator, able to complete all aspects of the study