Genetics of Chiari I Malformation. Syringomyelia is most often associated with Chiari I malformation. Chiari I malformation develops by an unknown process. Ectopia of the cerebellar tonsils (through the foramen magnum at the base of the skull), the defining characteristic of the Chiari I malformation, may result from abnormal development of the posterior fossa. In a clinical study of families with multiple members affected by the Chiari I malformation, we are using magnetic resonance imaging of the brain to evaluate for Chiari I malformation and measure the size of the osseous structures and volume of the posterior fossa. After phenotyping family members as being affected or unaffected by these traits, we collect DNA specimens from them for genotyping. In collaboration with our Associate Investigator Joan Bailey-Wilson, M.D., Ph.D., we submitted DNA samples of affected and control individuals for Whole Exome Sequence (WES) under the NHGRI NISC-funded flagship project. The samples originated from families in Russia and the United States with multiple members affected by Chiari I malformation. This data set consisted of whole exome data from 10 extended families with a total of 132 individuals (including samples that were previously sequenced). Preliminary filtering was performed by removing markers with a depth of less than 10, a quality score of less than 10, or a ratio of quality score to depth of less than 0.5 using Golden Helix software. Further filtering was performed using p-link; markers that were only genotyped in two people or less were removed, as were monomorphic markers. Sib-pair was used to remove any markers with Mendelian errors. All cleaning resulted in a total of 560,134 markers. Several dummy individuals were added to connect disjointed pedigrees. To perform multi-point analyses, the markers were mapped onto the Rutgers Map, version 3. Two point linkage analyses were performed using the program TwoPointLods. The genetic model used for the program was a disease allele frequency of 0.01 with a penetrance of 0.01/0.01/0.0 (meaning no phenocopies). This year we published our findings of a genome-wide significant signal on chromosome 1q43-44 (HLOD = 3.5) and 12q23 (HLOD = 3.3) in both sets of linkage analyses (1). Most interesting was that both signals were driven by a single (different) family. Both regions contain several linked exonic variants, including rare variants located in good candidate genes. The two significantly linked regions for small posterior fossa are the respective driving signal in two families and are potentially causal. Further laboratory work is needed to confirm the causality of the signals. Sanger sequencing will be performed by laboratories at the Surgical Neurology Branch to confirm the variant identified on WES. We then anticipate performing functional studies of the protein of interest to further elucidate if it is the causative variant. Finding one or more genetic loci that are associated with the Chiari I malformation would lead to a better understanding of the etiology of the Chiari I malformation. We recently co-authored an epidemiologic study with colleagues in Russia confirming increased prevalence of Chiari I malformation in a region of Tatarstan, Russia (2) We also co-authored a study that found an association of EPAS1-associate syndrome and Chiari I malformation (3), commenting on the role of abnormal posterior fossa development in the development of Chiari I malformation in that syndrome. We also explored the mechanism of neuraxial dysraphism in EPAS1-associated syndrome and suggested that it is related to improper mesenchymal transition (4). Treatment of Syringomyelia. A natural history study of patients with syringomyelia was initiated 10 years ago in which patients will be monitored annually for 5 years with neurological examinations, standard scales of pain and function, and MRI of the brain and spine. Patients receive specialized care for their condition, including surgery if necessary. This study will better define the outcome of patients with syringomyelia and will provide preliminary data to generate hypotheses for future hypothesis-driven studies. This study was amended to increase the protocol enrollment ceiling to 180 from the previous 120 subjects. Additional subjects were necessary because 17 of 120 subjects had withdrawn from the study and needed to be replaced and because more patients were needed to evaluate the natural history of various subgroups in the study, which now include: a) Chiari I malformation alone, observation subgroup; b) Chiari I malformation alone, surgical treatment subgroup; c) Chiari I malformation with syringomyelia, observation subgroup; d) Chiari I malformation with syringomyelia, surgery subgroup; e) non-Chiari related syringomyelia, observation subgroup; and f) non-Chiari related syringomyelia, surgery subgroup. The study finished enrollment last year and will be completed when all subjects finish 5 years of follow-up. This year we were part of a working group that established common data elements for use in Chiari I malformation clinical research (5). We also collaborated on a project describing the surgical significance of variations in tentorial venous anatomy (6). Pathophysiology of Syringomyelia We previously reported a study evaluating the morphologic features of the cerebellum and medulla oblongata before and 3-6 months after surgery in patients with Chiari I malformation and syringomyelia. After surgically expanding the posterior fossa, the abnormal shape of the cerebellum and medulla oblongata characteristic of the Chiari I malformation changed to a more normal appearance. These findings support the concept that the Chiari I malformation arises from lack of development of the posterior fossa rather than a primary neural abnormality. We subsequently published a paper with Linge et al. describing the physiologic changes in CSF flow at the foramen magnum that occur after surgical treatment in patients with Chiari I malformation. We also published a clinical study of the pathophysiology of primary spinal syringomyelia, a type of syringomyelia not associated with Chiari I malformation. A preliminary finding was that obstruction of the spinal subarachnoid space in primary spinal syringomyelia was associated with enlarged cerebrospinal fluid (CSF) pressure waves superior to the obstruction. Successful surgery for primary spinal syringomyelia opened CSF pathways, reduced CSF pressure waves to normal and resolved syringomyelia, as had successful surgery in our studies of Chiari I-type syringomyelia. This association suggests that primary spinal syringomyelia and Chiari I-type syringomyelia arise from a similar mechanism. We recently published a clinical study of CT-myelography that showed that syringes associated with obstruction of the spinal subarachnoid space had greater accumulation of myelography dye than syringes associated with intramedullary tumors, supporting greater communication of the subarachnoid space with the syrinx when the subarachnoid is obstructed than when an intramedullary tumor is present (7). This study supported the concept that syrinx fluid originates from the spinal subarachnoid space in syringes associated with spinal subarachnoid space obstruction.