Patricia Duffek

Abstract X-linked hypophosphatemia (XLH) is a rare, genetically determined disorder of phosphate metabolism, most commonly caused by mutations in the PHEX gene. These mutations lead to overexpression of the phosphaturic hormone FGF23, resulting in renal phosphate wasting and impaired bone mineralization. In up to 16% of clinically diagnosed cases, no causative variant can be identified using standard sequencing approaches.

1 Introduction More than 50 short tandem repeat (STR) expansion disorders are known, which are caused by pathogenic expansions of repetitive DNA sequences [1]. These STR expansions are composed of repetitive motifs of up to 9 bp and can encompass in total a size up to 40 kb, such as in the gene CNBP causing myotonic dystrophy [2]. STRs are located in coding regions, intronic, in the 3′ and 5′ UTR region, and in noncoding RNA.