In addition to hypogonadotropic hypogonadism, 44.4% (8/18) patients exhibited other clinical deformities, including dental agenesis (3/18, 16.7%), hearing loss (3/18, 16.7%), and hand malformation (2/18, 11.1%). hCG/hMG therapy was effective in promoting sexual development in IHH patients with FGFR1, FGF8, and FGF17 mutations.
Indeed, FGF8 and FGFR1 deficiency severely compromises vertebrate reproduction in mice and humans and is associated with Kallmann Syndrome (KS), a congenital disease characterized by hypogonadotropic hypogonadism associated with anosmia.
The present study provides further evidence that mutations and deletions in the known causative genes play a relatively minor role in the etiology of HH and that submicroscopic rearrangements encompassing FGFR1 can lead to IHH as a sole recognizable clinical feature.
Several themes have emerged as the genetic basis of HH has gradually been uncovered, including the association of some genes such as FGFR1, FGF8, PROK2 and PROKR2, both with HH in association with hyposmia/anosmia (Kallmann syndrome) and with normosmic HH, thus blurring the clinical distinction between ontogenic and purely functional defects in the axis.
One large heterozygous deletion involving all FGFR1 exons was identified in a female patient with sporadic normosmic hypogonadotropic hypogonadism and mild dimorphisms as ogival palate and cavus foot.
This report demonstrates 1) the first genetic cause of the rare variant of reversible KS, 2) the reversal of hypogonadotropic hypogonadism in a proband carrying an FGFR1 mutation suggests a role of FGFR1 beyond embryonic GnRH neuron migration, and 3) a loss of function mutation in the FGFR1 gene causing delayed puberty.
The results suggest the following: 1) KAL1 mutations might be more prevalent in the Japanese patients than previously estimated in the Caucasian patients and can be associated with apparently normal olfactory function; 2) FGFR1 mutations account for approximately 10% of KS patients, as previously reported in the Caucasian patients, and can result in HH and olfactory dysfunction-only phenotype; and 3) renal aplasia, which is characteristic of KAL1 mutations, and cleft palate and dental agenesis, which are characteristic of FGFR1 mutations, can occur in patients without KAL1 and FGFR1 mutations.