Urofacial syndrome (UFS; MIM# 236730) is a rare autosomal recessive condition characterised by urinary bladder and bowel voiding dysfunction with a pathognomonic abnormality of facial movement with expression. UFS can be caused by biallelic putative loss-of-function mutations in HPSE2, which encodes heparanase 2. Failure to discover HPSE2 mutations in all cases of UFS suggests genetic heterogeneity. The urinary tract features of UFS overlap those seen in the spectrum of non-syndromic non-neurogenic voiding dysfunction and vesicoureteric reflux (VUR). This overlap suggests there may be some aspects of pathogenesis in common. The project aimed to define the genotypic and phenotypic spectrum associated with mutations in HPSE2 by Sanger sequencing and multiplex ligation-dependent probe amplification (MPLA) in newly referred cases of UFS and making comparison to a review of mutations and phenotypes seen in the literature. This work discovered five further families with HPSE2 associated UFS increasing known mutations whilst, reinforced that this is an under-recognised condition and emphasised the previously under-reported feature of facial weakness. The failure to discover HPSE2 mutations in all cases referred provided further evidence of genetic heterogeneity. The project also aimed to discover further genes associated with UFS. Autozygosity mapping and whole exome sequencing was carried out in cases of UFS without mutations in HPSE2. This led to the recognition that UFS is also caused by biallelic putative loss-of-function mutations in LRIG2 encoding the leucine-rich repeats and immunoglobulin-like domains 2 (LRIG2) protein in three families. Failure to identify LRIG2 mutations in all HPSE2 negative families suggests further genetic heterogeneity. To address the question of whether the pathogenesis of UFS overlaps more common conditions with a similar spectrum of urinary tract abnormalities I aimed to examine whether pathogenic variants in HPSE2 and LRIG2 were seen in these phenotypes. Unexpectedly this led to the discovering of further families affected by UFS but failed to show an association of variants in UFS genes with non-syndromic urinary tract abnormalities. However, variants of potential interest were discovered. As part of work toward understanding the pathogenesis of UFS and designing a model to test the pathogenesis of sequence variants expression studies in a Xenopus tropicalis hpse2 knock-down model of UFS were carried out. The knock-down model provided valuable insight in to the likely pathogenesis of UFS with evidence pointing towards a congenital peripheral neuropathy with failure of correct nerve path finding. Understanding the pathogenesis of UFS has the potential to direct further research in to therapeutic intervention.

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