Hyperosmia, ectrodactyly, mild intellectual disability, and other defects in a male patient with an X-linked partial microduplication and overexpression of the KAL1 gene

Loss-of-function mutations of the KAL1 gene are a known cause of Kallmann syndrome, a disorder characterized by the coexistence of hypogonadotropic hypogonadism and anosmia/hiposmia. On the other hand, neither complete nor partial duplications of KAL1 have been reported in the literature; thus, clinical symptoms associated with such alterations remain unknown. Ectrodactyly is a clinically and genetically heterogeneous abnormality presenting with hypoplasia of the central rays of the extremity, which, in around 68 % of cases, has unknown underlying molecular defect. In this paper, we report on a sporadic male patient manifesting hyperosmia and ectrodactyly accompanied by additional symptoms involving mild intellectual disability, unilateral hearing loss, genital anomalies, stocky build, and facial dysmorphism. Using a combination of high-resolution array comparative genomic hybridization (array CGH) and breakpoint analysis, we detected a hemizygous tandem duplication of 110,967 bp on Xp22.31, encompassing the promoter region and the first two exons of KAL1. In order to confirm pathogenicity of the duplication, we tested the level of KAL1 transcript in blood lymphocytes, showing 79 times higher expression in the proband compared to controls. We, therefore, hypothesize that olfactory hypersensitivity in our proband directly results from KAL1 overproduction. Additionally, a literature review allowed us to conclude that KAL1 protein at high levels may interfere with FGFR1 signaling activity, most probably indirectly giving rise to ectrodactyly, intellectual disability, and genital anomalies. Noteworthy, those symptoms overlap with Hartsfield syndrome caused by FGFR1 loss-of-function mutations. To conclude, our paper highlights the role of KAL1 in embryogenesis and provides data on the contribution of KAL1 overexpression to human pathology.