Novel KAL1 sequence variants associated with septo-optic dysplasia (SOD) in three female patients (#197)
Background and aims: KAL1 is essential for GnRH neuronal migration and olfactory bulb development with mutations implicated in Kallmann syndrome (KS; hypogonadotrophic hypogonadism with anosmia). KAL1 is located in the X-chromosome pseudoautosomal region, which may account for the recent report of female KS patients exhibiting KAL1 variations.
There is increasing evidence of overlapping genotypes/phenotypes between KS and congenital hypopituitarism including septo-optic dysplasia (SOD). Therefore, we aimed to screen 421 patients with the latter for mutations in KAL1.
Methods: The coding region of KAL1 was assessed by direct sequencing. Functional analyses of identified variants included immunocytochemistry and western blot analyses for protein secretion from Cos7 cells as well as a novel quantitative luciferase-reporter assay.
Results: Two variants [p.K185N (n=1) and novel p.P291T (n=2; sisters)], occurring at highly conserved residues and absent from 480 controls, were identified in three female patients with SOD. Each had optic nerve hypoplasia and GH deficiency, with the p.K185N variant also being associated with TSH deficiency and an ectopic posterior pituitary. A qualitative decrease in secretion of mutant p.P291T protein was shown by its retention in some Cos7 cells and a 40% decrease in transcriptional activity (p<0.001). Secretion of p.K185N was unaffected but the variant was associated with a 21% decrease in transcriptional activity (p<0.01). This variant is located between protein-protein interaction domains and may affect the binding of the protein to FGFR1 and heparan sulfate. Both variants were inherited from the unaffected mothers and are suggestive of variable penetrance or digenicity in the affected individuals, none of whom exhibit variations in any of the other known KS genes.
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 variants.