REPORT Ciliary Abnormalities Due to Defects in the Retrograde Transport Protein DYNC2H1 in Short-Rib Polydactyly Syndrome Amy E. Merrill, 1,2 Barry Merriman, 3 Claire Farrington-Rock, 1 Natalia Camacho, 2 Eiman T. Sebald, 1 Vincent A. Funari, 1,4 Matthew J. Schibler, 7,8 Marc H. Firestein, 2 Zachary A. Cohn, 1 Mary Ann Priore, 1 Alicia K. Thompson, 9 David L. Rimoin, 1,3,4,5 Stanley F. Nelson, 3 Daniel H. Cohn, 1,3,4 and Deborah Krakow 1,2,3,6, * The short-rib polydactyly (SRP) syndromes are a heterogenous group of perinatal lethal skeletal disorders with polydactyly and multisystem organ abnormalities. Homozygosity by descent mapping in a consanguineous SRP family identified a genomic region that contained DYNC2H1, a cytoplasmic dynein involved in retrograde transport in the cilium. Affected individuals in the family were homozygous for an exon 12 missense mutation that predicted the amino acid substitution R587C. Compound heterozygosity for one missense and one null mutation was identified in two additional nonconsanguineous SRP families. Cultured chondrocytes from affected individuals showed morphologically abnormal, shortened cilia. In addition, the chondrocytes showed abnormal cytoskel- etal microtubule architecture, implicating an altered microtubule network as part of the disease process. These findings establish SRP as a cilia disorder and demonstrate that DYNC2H1 is essential for skeletogenesis and growth. Cilia are highly conserved microtubule-based organelles that project from the cell surface into the extracellular environment and play diverse roles in cellular motility, sensory transduction, and signaling. Cilia consist of a microtubule-based axoneme made of nine peripheral microtubule doublets arranged around a central core; motile cilia contain two central microtubules (9 þ 2), whereas nonmotile or primary cilia do not (9 þ 0). 1,2 During early stages of cilia formation, the centriolar vesicle docks at the plasma membrane to form the axonemal shaft and basal body. Further elongation and maintenance of the cilia is dependent on the dynamic process of intrafla- gellular transport (IFT). IFT bidirectionally transports ciliary cargo with the help of motors along the outer micro- tubules of the axoneme. Anterograde movement of axonemal precursors from the basal body to the distal tip is driven by the heterotrimeric kinesin-II motor. Retrograde transport from the distal tip to the basal body is accom- plished by the cytoplasmic dynein 2 complex. In humans and mice, ciliary dysfunction is associated with a large spectrum of disorders, 3–5 including defects in a variety of proteins necessary for IFT as well as in compo- nents of the primary cilia, basal body, and centrosome. Many of these phenotypes include polydactyly, and some include abnormal skeletogenesis. In particular, some cases of asphyxiating thoracic dystrophy (ATD [MIM 208500]) result from mutations in the gene encod- ing the anterograde transport protein IFT80 6 (MIM 611177). About two-thirds of patients with Ellis-van Cre- veld (EVC [MIM 225500]) syndrome have mutations in either EVC1 (MIM 604831) or EVC2 7–9 (MIM 607261), and the Evc1 gene product has been localized to the ciliary basal body in mouse chondrocytes, where it participates in hedgehog signal transduction. 10 The short-rib polydactyly syndromes are among the most frequent autosomal-recessive osteochondrodyspla- sias. 11 Four distinct types (SRP I [Saldino-Noonan type (MIM 263530)]; SRP II [Majweski type (MIM 263520)]; SRP III [Verma-Neumoff type (MIM 263510)]; and SRP IV [Beemer type (MIM 269860)]) are recognized, and the current nosology of the osteochondrodysplasias classifies types I and III together. 12 However, many cases defy classi- fication and demonstrate transitional findings between the types, suggesting that SRP could be considered a single group of disorders with a spectrum of variable phenotypic expression. 13–16 SRPs manifest extremely shortened long bones, a small, narrow thorax, and frequent pre- and post- axial polydactyly. Other multisystem anomalies, including brain and cardiac malformations (including situs inversus), polycystic kidneys, gastrointestinal and genitourinary atresia, and occasional sex reversal, are also observed. Although genetically distinct in some instances, 17 the SRPs share phenotypic and radiographic findings with ATD and EVC, supporting the hypothesis that these diseases comprise a family of disorders that may be func- tionally related. Under an IRB-approved protocol for human subjects, we ascertained a consanguineous family (International Skel- etal Dysplasia Registry reference number R01-314) with first-cousin parents and four affected offspring. Although 1 Medical Genetics Research Institute, Cedars-Sinai Medical Center, Los Angeles, CA, 90048; 2 Department of Orthopedic Surgery, 3 Department of Human Genetics, 4 Department of Pediatrics, 5 Department of Medicine, 6 Department of Obstetrics and Gynecology, 7 Brain Research Institute, 8 UCLA California NanoSystems Institute, David Geffen School of Medicine at UCLA, Los Angeles, CA, 90024; 9 Center for Electron Microscopy, University of Southern California, Los Angeles, CA, 90089 *Correspondence: dkrakow@mednet.ucla.edu DOI 10.1016/j.ajhg.2009.03.015. ª2009 by The American Society of Human Genetics. All rights reserved. 542 The American Journal of Human Genetics 84, 542–549, April 10, 2009