HPGD and skeletal system disorder: Autosomal recessive PHO 1 (PHOAR1, MIM: #259100) is characterized by childhood-onset primary digital clubbing, osteoarthropathy, and acro-osteolysis, with variable features of pachydermia, delayed closure of the fontanels, and congenital heart disease due to biallelic HPGD mutations in some patients.