recessive mutations in pthr1 cause contrasting skeletal dysplasias in eiken and blomstrand syndromes eiken syndrome is a rare autosomal recessive skeletal dysplasia we identified a truncation mutation in the cterminal cytoplasmic tail of the parathyroid hormone pthpthrelated peptide pthrp type 1 receptor pthr1 gene as the cause of this syndrome eiken syndrome differs from jansen and blomstrand chondrodysplasia and from enchondromatosis which are all syndromes caused by pthr1 mutations notably the skeletal features are opposite to those in blomstrand chondrodysplasia which is caused by inactivating recessive mutations in pthr1 to our knowledge this is the first description of opposite manifestations resulting from distinct recessive mutations in the same gene