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

Abstract

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 proteincoupled 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.

European Consensus Statement on congenital hypogonadotropic hypogonadism—pathogenesis, diagnosis and treatment

“…Genes encoding fibroblast growth factor 8 (FGF8) signalling pathway proteins, [17][18][19][20][21][22] chromodomain helicase DNA-binding protein 7 (CHD7) [23][24][25][26][27] and sex determining region Y-Box 10 (SOX10) 28,29 affect the neurogenic niche in the nasal area and craniofacial development. Conversely, Kallmann syndrome protein, which is now officially known as anosmin 1 (encoded by KAL1; following nomenclature change, the gene is now denoted as ANOS1), 2 prokineticin-2 and prokineticin receptor 2 (encoded by PROK2 and PROKR2, respectively), [30][31][32][33] WD repeat domain 11 (encoded by WDR11), 34,35 semaphorin 3A (encoded by SEMA3A) [36][37][38] and FEZ family zinc finger 1 (encoded by FEZF1) 39 influence migration of GnRH neurons.…”

“…117,118 To date, >25 different genes have been implicated in Kallmann syndrome and/or CHH, which accounts for ~50% of cases. 21 Causative genes for Kallmann syndrome include: KAL1 (ANOS1) in the X-linked form; FGFR1 (encoding fibroblast growth factor receptor 1), 17,18 FGF8, 19,119 CHD7, [23][24][25][26][27] HS6ST1 (encoding heparan-sulphate 6-O-sulphotransferase 1), 20 SOX10, 28,29 SEMA3A (encoding semaphorin-3A), [36][37][38] WDR11 (encoding WD repeat-containing protein 11) 34,35 and IL17RD (encoding interleukin-17 receptor D) 21 in the autosomal dominant form; and PROKR2 and/or PROK2, [30][31][32][33] and FEZF1 39 in the autosomal recessive form, even though it should be noted that most patients carrying mutations in PROKR2 or PROK2 carry these mutations in the heterozygous state. 120,121 Genes involved in CHH that are associated with a normal sense of smell include GNRHR (encoding gonadotropinreleasing hormone receptor), 122,123 GNRH1 (encoding gonadotropin-releasing hormone 1), 124,125 KISS1R, 41,42 KISS1, 40,126 TACR3 and TAC3.…”

“…Such an observation led to the hypothesis that multiple gene defects could synergize to produce a more severe CHH phenotype (that is, oligo genicity). 30,128 Studies in large CHH cohorts indicate that at least 20% of cases are oligogenic 11,21 (Table 1). …”

Kallmann syndrome

“…15,16 In some families, both typical KS phenotypes and dissociated phenotypes with either hypogonadism or anosmia have been described. 7,10,13,14,17 In addition, apparent reversal of the hypogonadism after discontinuation of hormonal treatment has been reported in a few KS patients. 9,18,19 Finally, a variety of non-reproductive non-olfactory additional anomalies are present in only a fraction of KS patients.…”

“…In the autosomal dominant form, incomplete penetrance has been emphasized. 5,61 Five causal genes have been identified to date, namely, by chronological order of discovery, KAL1, 62 -64 FGFR1, 7 PROKR2 and PROK2, 10 and FGF8. 65 Various loss-of-function mutations in KAL1, encoding the extracellular matrix glycoprotein anosmin-1, and in FGFR1 or FGF8, encoding fibroblast growth factor receptor-1 and fibroblast growth factor-8, underlie the X chromosome-linked form (KAL1) and an autosomal dominant form (KAL2) of KS, respectively (see Supplementary Tables S1, S2 and S3 for a list of the mutations).…”