ENPP1 and enthesopathy: Sanger sequencing for the variants identified in the first patient was then performed in her two sons (19 years old and 23 years old), both of whom were found to possess heterozygous Y451C ENPP1 pathogenic variants and Achilles tendon enthesopathies at their young age (Figure 3c), further demonstrating the association of enthesopathy and ENPP1 pathogenic variants.