Kallmann Syndrome: Mutations in the Genes Encoding Prokineticin-2 and Prokineticin Receptor-2

Kallmann syndrome combines anosmia, related to defective olfactory bulb morphogenesis, and hypogonadism due to gonadotropin-releasing hormone deficiency. Loss-of-function mutations in KAL1 and FGFR1 underlie the X chromosome-linked form and an autosomal dominant form of the disease, respectively. Mutations in these genes, however, only account for approximately 20% of all Kallmann syndrome cases. In a cohort of 192 patients we took a candidate gene strategy and identified ten and four different point mutations in the genes encoding the G protein-coupled prokineticin receptor-2 (PROKR2) and one of its ligands, prokineticin-2 (PROK2), respectively. The mutations in PROK2 were detected in the heterozygous state, whereas PROKR2 mutations were found in the heterozygous, homozygous, or compound heterozygous state. In addition, one of the patients heterozygous for a PROKR2 mutation was also carrying a missense mutation in KAL1, thus indicating a possible digenic inheritance of the disease in this individual. These findings reveal that insufficient prokineticin-signaling through PROKR2 leads to abnormal development of the olfactory system and reproductive axis in man. They also shed new light on the complex genetic transmission of Kallmann syndrome

Segregation of Kallmann Syndrome and the <i>PROKR2</i> or <i>PROK2</i> Mutations in Affected Families

<p>Filled symbols denote clinically affected individuals with both hypogonadism and anosmia (or hyposmia). Half-filled symbols denote individuals with either anosmia only (right black part) or hypogonadism only (left black part). Genotypes, if available, are indicated below. The symbol + denotes normal allele, and fs stands for frameshift mutation. In several pedigrees the mutation is associated with varying phenotypes. Notably, in family A the disease apparently segregates according to a semi-dominant mode of transmission. The schematic representation of PROKR2 shows the locations of the nine missense mutations found in familial and non-familial KS cases, with respect to the putative N-terminal (N ter), C-terminal (C ter), extracellular loop (e1-e3), intracellular loop (i1-i3), and transmembrane (T1–T7) domains [<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.0020175#pgen-0020175-b013" target="_blank">13</a>] of this G protein-coupled receptor.</p