Report of second case and clinical and molecular characterization of Eiken syndrome.

We report a boy with Eiken syndrome caused by a homozygous missense variant in Parathyroid hormone 1 receptor (PTH1R) c.103G > A [p.(Glu35Lys)]. Eiken syndrome is a very rare skeletal dysplasia due to bi-allelic variants in PTH1R. Only one affected family has been known to-date. The hallmarks include delayed ossification of bone including the epiphyses, pubic symphysis, and primary ossification centers of the short tubular bones, coarse bone trabeculae, and modeling abnormalities. The phenotype being described here recapitulates the delayed ossification and modeling abnormalities of Eiken syndrome. In addition, supernumerary epiphyses of the tubular bones of the hands and primary failure of eruption of teeth were observed in our proband. This report characterizes Eiken syndrome and confirms that bi-allelic hypomorphic variants in PTH1R are probably to cause this condition.