Background: Isolated gonadotropin-releasing hormone (GnRH) deficiency (IGD) is caused by a deficiency in GnRH production, secretion or action and a highly heterogeneous disorder with wide phenotypic spectrum including Kallmann syndrome (KS) with anosmia and normosmic idiopathic hypogonadotropic hypogonadism (nIHH). More than 30 different causative genes have been identified in several studies. FGFR1 mutations have been identified in about 310% of patients with Kallmann syndrome or nIHH. This study was performed to investigate the clinical phenotypes and to assess functional characteristics of FGFR1 mutations in patients with IGD.
Methods: Mutation analysis of FGFR1 was performed in 49 subjects with IGD using targeted gene panel for 69 genes (n = 34) or whole exome sequencing (n = 15). The impact of the identified mutations on FGFR1 function was assessed using in vitro studies.
Results: Six novel heterozygous mutations in FGFR1 were identified in 6 unrelated patients (12.2%): p.Y210*, p.Y339H, p.S681I, c.1855-1G>A, c.1663+2T>G, and c.551dup (p.N185Kfs*16). They exhibited a wide clinical spectrum with altered pubertal development, ranging from KS (n = 1), nIHH (n = 4), and a prepubertal male with anosmia. Four adult males manifested delayed puberty or micropenis, while a female subject presented with primary amenorrhea at age 19 years. A 7-year-old male presented with anosmia and absence of olfactory bulbs. Patients with p.Y339H and c.1855-1G>A revealed osteoporosis and finger syndactyly, respectively. Wild-type (WT) and FGFR1 mutants (p.Y339H and p.N185Kfs*16) were transiently transfected into L6 myoblasts with an FGFR1-responsive osteocalcin promoter luciferase construct. FGF8 treatment of WT FGFR1 induced an increase in LUC reporter gene expression. Total RNA was extracted from peripheral blood using a PAXgene blood RNA kit and RT-PCR was performed in the patients with a c.1663+2T>G mutation, resulting a skipping of exon 11.
Conclusions: This study identified six novel mutations in FGFR1 mutations in 12.2% of subjects with KS and nIHH. Inactivating mutations in FGFR1 occur at a high frequency in IGD patients. Probands carrying an FGFR1 mutation displayed a wide phenotypic spectrum ranging from KS to anosmia. A prepubertal male with anosmia should be followed up to assess pubertal development.
19 Sep 2019 - 21 Sep 2019