Oud et al. Cilia (2018) 7:1 https://doi.org/10.1186/s13630-018-0055-2 Cilia SHORT REPORT Open Access Cellular ciliary phenotyping indicates pathogenicity of novel variants in IFT140 and confrms a Mainzer–Saldino syndrome diagnosis Machteld M. Oud1,2* , Brooke L. Latour1,2‡, Zeineb Bakey1,2‡, Stef J. Letteboer1,2, Dorien Lugtenberg1, Ka Man Wu1,2, Elisabeth A. M. Cornelissen3, Helger G. Yntema1,4, Miriam Schmidts1,2,5, Ronald Roepman1,2† and Ernie M. H. F. Bongers1† Abstract Background: Mainzer–Saldino syndrome (MZSDS) is a skeletal ciliopathy and part of the short-rib thoracic dysplasia (SRTD) group of ciliary disorders. The main characteristics of MZSDS are short limbs, mild narrow thorax, blindness, and renal failure. Thus far, variants in two genes are associated with MZSDS: IFT140, and IFT172. In this study, we describe a 1-year-old girl presenting with mild skeletal abnormalities, Leber congenital amaurosis, and bilateral hear- ing difculties. For establishing an accurate diagnosis, we combined clinical, molecular, and functional analyses. Methods: We performed diagnostic whole-exome sequencing (WES) analysis to determine the genetic cause of the disease and analyzed two gene panels, containing all currently known genes in vision disorders, and in hearing impairment. Upon detection of the likely causative variants, ciliary phenotyping was performed in patient urine- derived renal epithelial cells (URECs) and rescue experiments were performed in CRISPR/Cas9-derived Ift140 knock out cells to determine the pathogenicity of the detected variants in vitro. Cilium morphology, cilium length, and intrafa- gellar transport (IFT) were evaluated by immunocytochemistry. Results: Diagnostic WES revealed two novel compound heterozygous variants in IFT140, encoding IFT140. Thor- ough investigation of WES data did not reveal any variants in candidate genes associated with hearing impairment. Patient-derived URECs revealed an accumulation of IFT-B protein IFT88 at the ciliary tip in 41% of the cells indicative of impaired retrograde IFT, while this was absent in cilia from control URECs. Furthermore, transfection of CRISPR/ Cas9-derived Ift140 knock out cells with an IFT140 construct containing the patient mutation p.Tyr923Asp resulted in a signifcantly higher percentage of IFT88 tip accumulation than transfection with the wild-type IFT140 construct. Conclusions: By combining the clinical, genetic, and functional data from this study, we could conclude that the patient has SRTD9, also called Mainzer–Saldino syndrome, caused by variants in IFT140. We suggest the possibility that variants in IFT140 may underlie hearing impairment. Moreover, we show that urine provides an excellent source to obtain patient-derived cells in a non-invasive manner to study the pathogenicity of variants detected by genetic testing. Keywords: Mainzer–Saldino syndrome, MZSDS, SRTD9, UREC, IFT140 *Correspondence: [email protected] †Ronald Roepman and Ernie M. H. F. Bongers Senior authors contributed equally to this work ‡Brooke Latour and Zeinab Bakey contributed equally to this work 1 Department of Human Genetics (855), Radboud University Medical Centre, PO‑Box 9101, 6500 HB Nijmegen, The Netherlands Full list of author information is available at the end of the article © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Oud et al. Cilia (2018) 7:1 Page 2 of 9 Background phenotype. By showing defective retrograde transport in Short-rib thoracic dysplasia (SRTD) refers to a group of patient-derived URECs and mutant IFT140 transfected ciliopathies characterized by skeletal abnormalities, that CRISPR/Cas9-derived Ift140 knockout cells, we confrm are classifed into 18 molecular subclasses; SRTD1-16, the clinical and molecular diagnosis of SRTD9/Mainzer– EVC, and EVC2. Te majority of genes mutated in SRTDs Saldino syndrome in this patient. encode intrafagellar transport (IFT) proteins, while a small subset encode proteins involved in hedgehog sign- Methods aling, ciliogenesis, or DNA damage response signaling Collection of samples [1–9]. IFT is required for cilium assembly, maintenance, Genomic DNA of patient II-3 was isolated from whole and disassembly. Two axonemal transport modules can blood and used for WES. Urine was collected from the be distinguished: the IFT-B complex, powered by the patient, her unafected parents, and three healthy con- kinesin-2 motor, for transport in anterograde direction trols to study the ciliary phenotype. (from ciliary base to tip), and the IFT-A complex, pow- ered by the dynein-2 motor, for retrograde transport Diagnostic whole-exome sequencing (from ciliary tip to base). Variants in genes encoding Diagnostic WES was performed as described previously subunits of the IFT-A particle are associated with SRTD [12]. In brief, we analyzed the vision disorder gene panel types 3–5, 7–9, 11, and 15 [1, 2, 4, 5, 8]. Te character- (version DG 2.3.2) and the hearing impairment gene istic skeletal fndings of SRTDs comprise short ribs and panel (version DG 2.3.2) [13, 14]. Exonic and intronic a narrow thorax and are often combined with short stat- positions − 20 till + 8 variants with a frequency < 5% ure, pelvic deformities, polydactyly, and brachydactyly. in dbSNP, < 1% in in-house database, and < 5% in the In addition to the skeletal abnormalities, other organ Exome Aggregation Consortium (ExAC) were evalu- systems can be involved including the kidneys, the liver, ated and classifed based on the guidelines for variant and the central nervous system [1]. Since the phenotypic classifcation determined by the Association for Clinical overlap between diferent SRTD subclasses is substan- Genetic Science (ACGS) [15]. Te same fltering strategy tial, the classifcation is based on the underlying genetic was used for the analysis of the complete WES dataset. defect and not on the clinical phenotype. Establishing an accurate diagnosis as early as possible is essential to Urine-derived renal epithelial cell isolation and culture provide the best-personalized care for the patient. For Te collection of urine, isolation of cells, and culturing example, monitoring renal function is likely to be more of URECs was performed as described previously [11]. important for patients carrying a pathogenic variant in In brief, midstream urine was collected and refriger- IFT140, TTC21B, or WDR19 than for patients who carry ated for up to 4 h. Cells were retrieved from the urine, DYNC2H1 or IFT80 variants, as the latter two are pri- washed once, and cultured in 1 ml primary UREC culture marily associated with a skeletal phenotype and IFT140, medium consisting of a 1:1 ratio Dulbecco’s Modifed TTC21B, and WDR19 are associated with a skeletal phe- Eagle’s medium (DMEM): Ham’s F12 Nutrient Mix con- notype accompanied by renal insufciency and retinal taining 10% FCS, 0.1 mg/ml Primocin (ant-pm-2, Invivo- degeneration [2, 10]. gen, Toulouse, France), and 1× REGM SingleQuots and Te efect of variants in ciliary genes can be studied at growth factors (CC-4127, Lonza; Basel, Switzerland) in a the protein level by analyzing the ciliary phenotype in 24-well plate. Cells were incubated at 37 °C with 5% CO2 patient-derived cells. Skin biopsies are commonly used and 0.5 ml primary UREC culture medium was added 24, to obtain patient-derived fbroblasts; however, this is an 48, and 72 h after cell isolation. At 96 h after cell isola- invasive and painful procedure. In 2015, Ajzenberg et al. tion, half of the culture medium was replaced by UREC reported on a non-invasive method to obtain patient- proliferation medium consisting of REBM Basal Medium derived cells from urine [11]. Urine-derived renal epi- (CC-3191, Lonza; Basel, Switzerland) containing 1× thelial cells (URECs) can be used to study the ciliary REGM SingleQuots and growth factors, and 0.1 mg/ml phenotype and are an excellent alternative for fbroblasts. Primocin. Every day for up to 14 days, half of the cul- In addition, since the development of cystic kidneys is ture medium was replaced with fresh UREC proliferation one of the hallmarks of ciliopathies, it is benefcial to medium until the URECs were visible and at approxi- study the ciliary phenotype in cells that originate from mately 80% confuence. this afected organ. In this study, we describe the use of URECs and Ciliary phenotyping in URECs CRISPR/Cas9 knockout cell lines to determine the To determine the ciliary phenotype of the patient, pathogenicity of two novel missense variants in IFT140 healthy family members, and controls, URECs were in a 1-year-old girl clinically diagnosed with a SRTD analyzed for cilium morphology, length, and IFT. Oud et al. Cilia (2018) 7:1 Page 3 of 9 Immunocytochemistry was used to visualize the cilia as and genomic DNA was extracted to check for variants described previously [16]. In short, URECs were cultured in Ift140 by Sanger sequencing upon PCR amplifca- on glass coverslips until they reached ~ 80% confuence. tion of the region around the targeted sequence (Addi- After fxation, permeabilization, and blocking, the cov- tional fle 1: Figure S2). Immunoblotting was performed erslips were incubated with primary antibodies targeting to validate the knocking out of IFT140 on protein level. IFT88 at 1:100 dilution (rabbit, 13967-1-AP, Protein- Protein lysates were made from CRISPR/Cas9 negative tech Group, Manchester, UK), IFT140 at 1:100 dilution control cells and CRISPR/Cas9-derived Ift140 knockout (rabbit, 17460-1-AP, Proteintech Group), acetylated-α- cells with or without transfection of the IFT140-Myc- tubulin at 1:1000 (mouse, T6793, Sigma-Aldrich, Zwi- DDK construct (NM_014714, cat# RC207528, OriGene, jndrecht, Netherlands), and RPGRIP1L at 1:500 dilution Herford, Germany).