Exome Sequencing Identifies WDR35 Variants Involved in Sensenbrenner Syndrome

Abstract

Sensenbrenner syndrome/cranioectodermal dysplasia (CED) is an autosomal-recessive disease that is characterized by craniosynostosis and ectodermal and skeletal abnormalities. We sequenced the exomes of two unrelated CED patients and identified compound heterozygous mutations in WDR35 as the cause of the disease in each of the two patients independently, showing that it is possible to find the causative gene by sequencing the exome of a single sporadic patient. With RT-PCR, we demonstrate that a splice-site mutation in exon 2 of WDR35 alters splicing of RNA on the affected allele, introducing a premature stop codon. WDR35 is homologous to TULP4 (from the Tubby superfamily) and has previously been characterized as an intraflagellar transport component, confirming that Sensenbrenner syndrome is a ciliary disorder.

Sensenbrenner syndrome (Cranioectodermal dysplasia): Clinical and molecular analyses of 39 patients including two new patients

“…Patient 2 with the novel compound heterozygous variants of WDR35 had a unique multisutural craniosynostosis. Although the first two patients reported with WDR35 mutations lacked renal and liver disease [Gilissen et al, 2010], one-third (2/6) in the current series have liver involvement, which increases if one includes the 3 additional sibs reported by Bacino et al [2012] who had the distinctive ciliopathy phenotype of malformation of the ductal plate, bile duct proliferation, fibrosis, cholestasis, and cirrhosis. Similarly, Bacino et al [2012] and Hoffer et al [2013] also describe patients with WDR35 mutations with cystic kidney disease.…”

“…WES identified compound heterozygous variants in the WDR35 gene (RefSeq NM_001006657) at c.3091C>T (p.H1031Y) in exon 26 and c3203A>G (p.Y1068C) in exon 27. These variants are likely the cause of disease as mutations in this gene have previously been detected in Sensenbrenner syndrome [Gilissen et al, 2010;Bacino et al, 2012;Hoffer et al, 2013]. The two variants were indeed novel and never reported in any known mutation database.…”

“…Because of the skeletal and ectodermal anomalies, it has been referred to as cranioectodermal dysplasia (CED) [Gellis and Feingold, 1979;Savill et al, 1997;Tamai et al, 2002;Obikane et al, 2006;Fry et al, 2009;Konstantinidou et al, 2009], but for this study, we use the eponym Sensenbrenner syndrome. There is significant phenotypic variability and dramatic advances using microarray analysis and targeted-and whole-exome sequencing (WES) have demonstrated molecular heterogeneity [Gilissen et al, 2010;Walczak-Sztulpa et al, 2010;Arts et al, 2011;Bredrup et al, 2011;Hoffer et al, 2013], and showed that this syndrome is probably due to cilia dysfunction [Baker and Beales, 2009;Konstantinidou et al, 2009;Walczak-Sztulpa et al, 2010;Hildebrandt et al, 2011]. OMIM currently lists four molecular subtypes as CED1 (#218330, chr 3q221.3-q22.1, IFT122), CED2 (#613610, chr 2p24.1, WDR35), CED3 (#614099, chr 14q24.3, IFT43), and CED4 (#614378, chr 4p14, WDR19).…”

Disease gene identification strategies for exome sequencing

“…After this, typically between 150 and 500 private non-synonymous or splicesite variants are prioritized as potential pathogenic variants (see Figures 1 and 2). 4,[28][29][30][31][32][33][34] It is important to emphasize that prioritization may discard the pathogenic variant. A variant that is present at low frequency in a heterozygous state in the normal population may be removed even though it causes disease if present in a homozygous state.…”

A compound heterozygous mutation in DPAGT1 results in a congenital disorder of glycosylation with a relatively mild phenotype

“…We then applied a prioritization scheme similar, as described earlier, in order to identify the pathogenic mutation. 12 To this end, we excluded variants known in dbSNPv132, as well as variants from our inhouse database. The latter consisted of 369 exome samples from healthy individuals and patients with other rare diseases.…”