This hypothesis was further supported when a patient with Kallmann syndrome was discovered to carry the same PROKR2 heterozygous mutation as our proband, p.R85C, in combination with a second heterozygous mutation in FGFR1, c.1810G>A;p.A604T (NM_023110.2), thereby providing evidence for a digenic basis for the syndrome (22). This evidence concerns the gene PROKR2 and Kallmann syndrome.