Endocrine Abstracts

Introduction: KAL1 is essential for GnRH neuronal migration and olfactory bulb development, and mutations within this gene have been implicated in 5% of Kallmann syndrome (KS) cases, a disorder characterized by the association of hypogonadotrophic hypogonadism with anosmia. It is the only identified X-linked form of the disorder and as a result only KS males had been screened for mutations until recently, when females exhibiting KS phenotypes were screened and subsequently tested positive for KAL1 variations.

Objective: Given apparent overlaps in phenotypes and genotypes between KS and hypopituitarism disorders including SOD and craniofacial defects, we aimed to screen such patients (n=421, M:F; 1.1:1) for mutations in KAL1.

Methods: Direct sequencing analysis was used to screen the coding region of KAL1. Any variants identified were tested using appropriate functional assays. These included investigation of mutational effects on protein secretion analysed qualitatively by immunocytochemistry (ICC) using GFP-labelled KAL1 in Cos7 cells, and western blot analysis.

Results: Three female patients with SOD tested positive for novel mutations in KAL1, absent from 480 controls, at highly conserved residues; p.K185N (n=1) and p.P291T (n=2 (sisters)). All children had optic nerve hypoplasia and GHD, with the p.K185N mutation also being associated with TSHD and an ectopic posterior pituitary. The p.P291T mutation is located between the first two fibronectin domains and we observed a qualitative decrease in secretion of the resultant protein as shown by its retention in Cos7 cells by ICC and western blot analysis. No change in secretion was observed for p.K185N. The p.K185N mutation is located between the WAP and first fibronectin domains of KAL1 and is predicted to affect the binding of the protein to FGFR1 and heparin sulfate. Binding studies are currently ongoing. Both mutations were transmitted by the unaffected mothers. This may reflect variable penetrance or skewed X-inactivation in the affected patients.

Conclusion: We implicate KAL1 in females with hypopituitarism/SOD for the first time to our knowledge, reflecting an overlap between KS and SOD that has also been observed with FGF8, FGFR1 and PROKR2 mutations.