REPORT Exome Sequencing Identifies Autosomal-Dominant SRP72 Mutations Associated with Familial Aplasia and Myelodysplasia Michael Kirwan, 1,2,6, * Amanda J. Walne, 1,2,6 Vincent Plagnol, 3 Mark Velangi, 4 Aloysius Ho, 5 Upal Hossain, 1,2 Tom Vulliamy, 1,2,7 and Inderjeet Dokal 1,2,7 Aplastic anemia (AA) and myelodysplasia (MDS) are forms of bone marrow failure that are often part of the same progressive underlying disorder. While most cases are simplex and idiopathic, some show a clear pattern of inheritance; therefore, elucidating the underlying genetic cause could lead to a greater understanding of this spectrum of disorders. We used a combination of exome sequencing and SNP haplotype analysis to identify causative mutations in a family with a history of autosomal-dominant AA/MDS. We identified a hetero- zygous mutation in SRP72, a component of the signal recognition particle (SRP) that is responsible for the translocation of nascent membrane-bound and excreted proteins to the endoplasmic reticulum. A subsequent screen revealed another autosomal-dominant family with an inherited heterozygous SRP72 mutation. Transfection of these sequences into mammalian cells suggested that these proteins localize incorrectly within the cell. Furthermore, coimmunoprecipitation of epitope-tagged SRP72 indicated that the essential RNA component of the SRP did not fully associate with one of the SRP72 variants. These results suggest that inherited mutations in a component of the SRP have a role in the pathophysiology of AA/MDS, identifying a third pathway for developing these disorders alongside transcription factor and telomerase mutations. Aplasia, or aplastic anemia (AA [MIM 609135]), is a condition in which bone marrow cells fail to produce a sufficient number of mature cells because of either retarded develop- ment or a cessation of regeneration. Myelodysplasia, or myelodysplastic syndrome (MDS [MIM 614286]), is the description given to a form of bone marrow failure in which immature cells in the bone marrow become malformed and dysfunctional. 1 These disorders are often part of a continuum beginning with AA, progressing through MDS, and in some cases ultimately transforming into acute myeloid leukemia (AML [MIM 601626]). Most cases of AA are simplex and idiopathic and MDS is relatively common in the aged population. However, some cases of AA/MDS (that is, AA and MDS as part of a disease continuum) are shown to be familial by presentation in several members of a family through more than one generation and early onset of disease symptoms. The underlying genetic causes of AA/ MDS are varied, and the genes involved in familial cases include the hematopoietic transcription factors RUNX1 (MIM 151385) 2 and GATA2 (MIM 137295) 3 and the telome- rase components TERC (MIM 602322) 4 and TERT (MIM 187270). 4 A mutation in the transcription factor CEBPA (MIM 116897) has also been identified in several cases of familial AML. 5 Many cases, however, remain uncharacter- ized at the genetic level; hence, we sought to analyze families with a history of AA/MDS for inherited mutations. We initially chose to screen a family (designated family 1) of four individuals affected by bone marrow failure and congenital nerve deafness with an apparent auto- somal-dominant mode of inheritance. The index case (II-1) was diagnosed with aplastic anemia by bone marrow biopsy, and two of her siblings (II-2 and II-3) were shown to be pancytopenic on the basis of full blood counts. One sibling with normal hearing had normal blood counts (II-4). The mother (I-2) had myelodysplasia (Figure 1A). The first analysis performed was a SNP typing approach. Genomic DNA samples, prepared from peripheral blood and extracted from all members of family 1 with the Puregene DNA isolation kit (Gentra, Minneapolis, MN, USA), were analyzed using the Illumina 6K SNP chip (service provided by The Genome Centre, Barts and The London School of Medicine). All samples were obtained with informed consent and the approval of our local ethics committee. Analyzing the data with Genehunter 6 through the use of an autosomal-dominant inheritance pattern over 20 regions within the genome gave a positive maximum LOD score of 0.9, so this family was not power- ful enough to give a unique location without large amounts of follow-up work. With the advent of whole-exome sequencing, the four affected members of the family were reevaluated. Approx- imately 180,000 coding exons from 5 mg of genomic DNA from each affected individual were captured with the NimbleGen SeqCap EZ exome library (Roche NimbleGen, Madison, WI, USA). After cluster generation, the exome DNA library was then sequenced on the Illumina Genome 1 Barts and The London School of Medicine and Dentistry, Queen Mary, University of London, London E1 2AT, UK; 2 Barts and The London Children’s Hospital, The Royal London Hospital, London E1 1BB, UK; 3 University College London Genetics Institute, London WC1E 6BT, UK; 4 Department of Clinical and Laboratory Haematology, Birmingham Children’s Hospital, Birmingham B4 6NH, UK; 5 Department of Haematology, Singapore General Hospital, Singapore 169 608, Singapore 6 These authors contributed equally to this work 7 These authors contributed equally to this work *Correspondence: m.j.kirwan@qmul.ac.uk DOI 10.1016/j.ajhg.2012.03.020. Ó2012 by The American Society of Human Genetics. All rights reserved. 888 The American Journal of Human Genetics 90, 888–892, May 4, 2012