Novel FGFR1 sequence variants in Kallmann syndrome, and genetic evidence that the FGFR1c isoform is required in olfactory bulb and palate morphogenesis.

In a new cohort of 141 unrelated patients affected by Kallmann syndrome we identified FGFR1 sequence variants in 17 patients, all in the heterozygous state. The fifteen novel variants consist of 10 missense (p.N77K, p.C101F, p.R250W, p.G270D, p.P283R, p.S332C, p.H621R, p.S685F, p.I693F, p.R822C), two nonsense (p.E324X, p.R661X), a frameshift (p.S439fs), and two splice site (c.1081G>C and c.1977+1G>A) changes. However, the p.N77K and p.R822C changes were also found in two and one out of 150 healthy control individuals, respectively, and therefore, their pathogenic effect is questionable. Notably, three alterations (p.E324X, p.S332C, c.1081G>C) are located in the alternative exon 8B that codes for the FGFR1c isoform, thus indicating that this isoform plays a crucial role in the development of the olfactory system in man. Moreover, the presence of cleft palate in a patient carrying the p.E324X change shows that FGFR1c is important for palate morphogenesis too.

Kallmann syndrome: 14 novel mutations in KAL1 and FGFR1 (KAL2).

Kallmann syndrome (KAL) combines hypogonadotropic hypogonadism and anosmia. Hypogonadism is due to Gonadotropin Releasing Hormone (GnRH) deficiency and anosmia is related to hypoplasia of the olfactory bulbs. Occasional symptoms include renal agenesis, bimanual synkinesia, cleft lip palate, dental agenesis. KAL is genetically heterogeneous and two genes have so far been identified, namely KAL1 (Xp22.3) and FGFR1/KAL2 (8p12), which underlie the X chromosome-linked form and an autosomal dominant form of the disease, respectively. We studied a cohort of 98 unrelated Caucasian KAL patients. We identified KAL1 mutations in 14 patients, of which 7 (c.3G>A (p.M1?), g.IVS1+1G>T, c.570_571insA (p.R191fsX14), c.784G>C (p.R262P), c.958G>T (p.E320X), c.1651_1654delinsAGCT (p.P551_E552delinsSX), c.1711T>A (p.W571R)) have not been previously reported. In addition, we found FGFR1 mutations in 7 patients, namely c.303G>A (p.V102I), C.385A>C (p.D129A), c.810G>A (p.V273M), c.1093_1094delAG (p.R365fsX41), c.1561G>A (p.A520T), c.1836_1837insT (p.Y613fsX42), c.2190C>G (p.Y730X), all of which were novel mutations. In this study, unilateral renal agenesis and bimanual synkinesia were exclusively found associated with KAL1mutations, cleft palate and dental agenesia with FGFR1mutations.