Mutations in fibroblast growth factor receptor 1 cause both Kallmann syndrome and normosmic idiopathic hypogonadotropic hypogonadism

Abstract

Mutations in KAL1 and FGFR1 cause Kallmann syndrome (KS), whereas mutations in the GNRHR and GPR54 genes cause idiopathic hypogonadotropic hypogonadism with normal olfaction (nIHH). Mixed pedigrees containing both KS and nIHH have also been described; however, the genetic cause of these rare cases is unknown. We examined the FGFR1 gene in seven nIHH subjects who either belonged to a mixed pedigree (n = 5) or who had associated midline defects (n = 2). Heterozygous FGFR1 mutations were found in three of seven unrelated nIHH probands with normal MRI of the olfactory system: (i) G237S in an nIHH female and a KS brother; (ii) (P722H and N724K) in an nIHH male missing two teeth and his mother with isolated hyposmia; and (iii) Q680X in a nIHH male with cleft lip/palate and missing teeth, his brother with nIHH, and his father with delayed puberty. We show that these mutations lead to receptor loss-of-function. The Q680X leads to an inactive FGFR1, which lacks a major portion of the tyrosine kinase domain (TKD). The G237S mutation inhibits proper folding of D2 of the FGFR1 and likely leads to the loss of cell-surface expression of FGFR1. In contrast, the (P722H and N724K) double mutation causes structural perturbations in TKD, reducing the catalytic activity of TKD. We conclude that loss-of-function mutations in FGFR1 cause nIHH with normal MRI of the olfactory system. These mutations also account for some of the mixed pedigrees, thus challenging the current idea that KS and nIHH are distinct entities.

Conflict of interest statement

Conflict of interest statement: No conflicts declared.

Figures

Fig. 1.

Detection of FGFR1 mutations in pedigree nos. 2, 4, and 7. Pedigree no. 2 reveals a mixed family, with both the proband and her brother carrying a heterozygous missense mutation in FGFR1 (G237S). Pedigree no. 4 reveals a mixed pedigree, with the proband and his mother carrying a heterozygous double mutation in FGFR1 (P722H and N724K). Pedigree no. 7 is consistent with familial nIHH and an autosomal dominant mode of inheritance. The proband, his brother, and his father carry a heterozygous mutation in FGFR1 (Q680X). The proband is identified by the arrow. Circles denote females; squares denote males. Phenotypes are as described in the text.

Fig. 2.

Mapping of the G237S mutation onto the crystal structure of the extracellular ligand-binding domain of FGFR1 in complex with FGF ligand and heparin oligosaccharide. (A) The G237S substitution maps to the βF–βG turn within D2 in the extracellular ligand binding region of FGFR1. A close-up view of the Gly-237 locus shows that both backbone nitrogen and carbonyl oxygen of Gly-237 engage in intramolecular hydrogen bonds, which play a critical role in shaping the local fold of the βF–βG turn of D2. Dashed lines represent hydrogen bonds. NT and CT, N terminus and C terminus of FGFR, respectively. FGF is colored orange, and receptor D2, D3, and D2–D3 linker are in green, cyan, and gray, respectively. Heparin oligosaccharides are rendered as sticks. Nitrogen, oxygen, and sulfur atoms are colored blue, red, and yellow, respectively. Carbon atoms of heparin oligosaccharides are colored black, and carbon atoms of the receptor are colored according to the subdomains to which they belong. This figure was made by using pymol (PyMOL Molecular Graphics System; DeLano Scientific, San Carlos, CA). (B) Comparison of the amino acid glycine at position 237 (red) across different species and within the FGFR family.

Fig. 3.

Structural and biochemical analysis of the Q680X mutation and the double (P722H and N724K) mutation in the FGFR1 gene. (A) The Q680X nonsense mutation and the (P722H and N724K) missense mutation map to the C-terminal lobe of the TKD. The Q680X mutation will delete a major portion of TKD. The (P722H and N724K) mutation maps to the loop region between αG and αH. These two residues play roles in shaping the conformation of this loop region and effectively preserving the catalytic activity the TKD. Note that the aliphatic side chain of P722 engages in numerous hydrophobic contacts with residues in αF and αH and indirectly contributes to the proper positioning of the residues at the active site of kinase domain. In contrast, Asn-724 is solvent exposed and engages in a single hydrogen bond with S723. Dashed lines represent hydrogen bonds. N-terminal and C-terminal kinase lobes are colored green and cyan, respectively. The hinge region and the regulatory activation loop of the kinase are colored gray and red, respectively. Nitrogen, oxygen, and sulfur atoms are colored blue, red, and yellow, respectively. Dotted spheres represent the van der Waals radius of selected residues. This figure was made by using pymol. (B) Comparison of the amino acid sequences, including arginine at position 680, proline at position 722, and asparagine at position 724 (red) across different species and within the FGFR family. (C) Tyrosine kinase activity of the double mutant FGFR1 (P722H and N724K) as compared with the wild-type FGFR1.

Fig. 4.

Neuroendocrine assessment of the proband with a double mutation (P722H and N724K) (A) and the proband with a nonsense mutation (Q680X) (B). An overnight 10-min sampling study for LH depicts endogenous LH secretion. Arrowheads indicate LH pulses, and the normal range of serum LH is hatched.