Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2016
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements of the Company and its subsidiaries have been prepared in conformity with accounting principles generally accepted in the United States of America ("GAAP"). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification ("ASC") and Accounting Standards Update ("ASU") of the Financial Accounting Standards Board ("FASB"). These consolidated financial statements are presented in U.S. Dollars.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the valuation of common stock, stock warrants and restricted stock, and the grant date fair value of stock options. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from such estimates.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company generally invests its cash equivalents in checking accounts and money market funds held at mid-sized financial institutions. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist of cash, deposits with banks and short term highly liquid money market instruments with remaining maturities at the date of purchase of 90 days or less.
Property and Equipment	Property and Equipment Property and equipment consists of construction in progress associated with the Company's investment in its manufacturing facility, office furniture and equipment and is recorded at cost less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred. Upon disposal, retirement or sale, the related cost and accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the results of operations. Property and equipment are depreciated on a straight-line basis over their estimated useful lives. The Company uses a life of five to ten years for office furniture and equipment.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. The Company did not record an impairment during the year ended December 31, 2016.
Segment Information	Segment Information The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company's singular focus is on developing and commercializing gene therapy treatments for patients suffering from rare and life-threatening neurological genetic diseases. All of the Company's tangible assets are held in the United States.
Revenue Recognition	Revenue Recognition To date, the Company has not generated any revenues from the commercial sale of its gene therapy product candidate.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries, stock-based compensation and benefits, third party license fees, and external costs of outside vendors engaged to conduct manufacturing and preclinical development activities and clinical trials. Upfront and milestone payments made to third parties who perform research and development services on the Company's behalf are expensed as services are rendered or when they no longer have alternative future use. Costs incurred in obtaining technology licenses are charged to research and development expense as acquired in-process research and development if the technology licensed has not reached technological feasibility and has no alternative future use.
Patent Costs	Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for its stock-based compensation awards in accordance with FASB ASC Topic 718, Compensation—Stock Compensation ("ASC 718"). ASC 718 requires all stock-based payments to employees, including grants of employee stock options and restricted stock units, to be recognized in the consolidated statements of operations based on their fair values. The Company's stock-based awards are subject to service and performance-based vesting conditions. Compensation expense related to awards to employees with only service-based vesting conditions is recognized on a straight-line basis over the requisite service period for each separately vesting portion of the award as if the award was, in substance, multiple awards (the "Graded Vesting Attribution Method"), based on the estimated grant date fair value for each separately vesting tranche. Compensation expense related to awards to non-employees with only service-based vesting conditions is recognized based on the then-current fair value at each financial reporting date prior to the measurement date over the associated service period of the award, which is generally the vesting term, using the Graded Vesting Attribution Method. Compensation expense related to awards to employees with only performance-based vesting conditions is recognized based on the estimated grant date fair value over the requisite service period using the Graded Vesting Attribution Method to the extent achievement of the performance condition is probable. Compensation expense related to awards to non-employees only with performance-based vesting conditions is recognized based on the then-current fair value at each financial reporting date prior to the measurement date over the requisite service period using the Graded Vesting Attribution Method to the extent achievement of the performance condition is probable. The Company estimates the fair value of its option awards to employees and directors using the Black-Scholes option-pricing model, which requires the input of and use of subjective assumptions, including (i) the fair value of the underlying common stock, (ii) the expected stock price volatility, (iii) the calculation of expected term of the award, (iv) the risk-free interest rate, and (v) expected dividends. Due to the lack of company-specific historical and implied volatility data of its common stock, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. When selecting these public companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected term of the stock-based awards. The Company computes historical volatility data using the daily closing prices for the selected companies' shares during the equivalent period of the calculated expected term of the stock-based awards. The Company's estimates of expected term used in the Black-Scholes option pricing model were based on the estimated time from the grant date to the date of exercise. The risk-free interest rates for periods within the expected term of the option are based on the U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The Company has never paid dividends, and does not expect to pay dividends in the foreseeable future. The Company is also required to estimate forfeitures at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from its estimates. To date, a forfeiture rate of zero has been used to calculate stock-based compensation expense due to the Company's lack of historical experience. To the extent that actual forfeitures differ from the Company's estimates, the differences are recorded as a cumulative adjustment in the period the estimates were revised. Stock-based compensation expense recognized in the consolidated financial statements is based on awards that are ultimately expected to vest. Stock-based awards issued to non-employees, consisting of stock warrants and restricted common shares, are accounted for using the fair value method in accordance with ASC 505-50, Equity-Based Payments to Non-Employees. These stock warrants and restricted common shares have been granted in exchange for consulting services to be rendered, and vest according to certain service or performance conditions. In accordance with authoritative guidance, the fair value of non-employee stock-based awards is estimated on the date of grant, and subsequently revalued at each reporting period until the award vests or a measurement date has occurred using the Black-Scholes option-pricing model.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders' equity (deficit) that result from transactions and economic events other than those with stockholders. There was no difference between net loss and comprehensive loss for each of the periods presented in the accompanying consolidated financial statements.
Income Taxes	Income Taxes The Company is a C corporation for federal and state income tax purposes. The Company recognizes deferred tax assets and liabilities for temporary differences between the financial reporting basis and the tax basis of its assets and liabilities and the expected benefits of net operating loss carryforwards. The impact of changes in tax rates and laws on deferred taxes, if any, is applied during the years in which temporary differences are expected to be settled and is reflected in the consolidated financial statements in the period of enactment. The measurement of deferred tax assets is reduced, if necessary, if, based on weight of the evidence, it is more likely than not that some, or all, of the deferred tax assets will not be realized. At December 31, 2016, 2015 and 2014, the Company has concluded that as a result of the accumulated losses to date and no near-term prospects for recognizing net income, a full valuation allowance is necessary for its deferred tax assets.
Fourth Amended and Restated Certificate of Incorporation	Fourth Amended and Restated Certificate of Incorporation On February 1, 2016, the Company amended its certificate of incorporation such that the total authorized capital stock of the Company consisted of 30,000,000 shares of common stock, $0.0001 par value per share, 3,278,938 shares of Class B-1 preferred stock, $0.0001 par value per share, 326,557 shares of Class B-2 preferred stock, $0.0001 par value per share, 2,365,020 shares of Class C preferred stock, $0.0001 par value per share, 3,105,000 shares of Class D preferred stock, $0.0001 par value per share and 1,000,000 shares of preferred stock, $0.0001 par value per share. Additionally, the Company effected a stock split whereby each outstanding share of common stock and Class B-1, B-2, C and D preferred stock was converted into 1.38 shares of common stock and Class B-1, B-2, C and D preferred stock, respectively. All share and per share information presented in these condensed consolidated financial statements and accompanying footnotes has been retroactively adjusted to reflect the stock split.
Fifth Amended and Restated Certificate of Incorporation	Fifth Amended and Restated Certificate of Incorporation On February 17, 2016, the Company amended its certificate of incorporation such that the total authorized capital stock of the Company consisted of 100,000,000 shares of common stock, $0.0001 par value per share, and 10,000,000 shares of preferred stock, $0.0001 par value per share.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the FASB and the International Accounting Standards Board (IASB) issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606). The standard's core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under previous guidance. Early adoption is permitted after December 15, 2016, and the standard is effective for public entities for annual reporting periods beginning after December 15, 2017 and interim periods therein. The Company has not recognized revenue through December 31, 2016. The Company will evaluate the adoption of ASU 2014-09 when the Company begins to recognize revenue and determine the effects it may have on the Company's consolidated financial statements. In June 2014, the FASB issued ASU No. 2014-12, Compensation—Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could be Achieved after the Requisite Service Period ("ASU 2014-12"), which requires the Company to assess share-based awards with performance targets that could be achieved after the requisite service period for potential treatment as performance conditions. Under ASU 2014-12, compensation expense is to be recognized when the performance target is deemed probable and should represent the compensation expense attributable to the periods for which service has already been rendered. If the performance target is reached prior to achievement of the service period, the remaining unrecognized compensation cost should be recognized over the remaining service period. ASU 2014-12 is effective for annual and interim periods beginning after December 15, 2015, with early adoption permitted. The Company has adopted ASU 2014-12, which did not have a material effect on the Company's consolidated financial statements. In August 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standard Update ("ASU") No. 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern ("ASU 2014-15"), requiring management to evaluate whether events or conditions could impact an entity's ability to continue as a going concern for at least one year after the date that the financial statements are issued and to provide disclosures if necessary. Disclosures will be required if conditions give rise to substantial doubt and the type of disclosure will be determined based on whether management's plans will be able to alleviate the substantial doubt. ASU 2014-15 is effective for the Company beginning for annual periods ending after December 15, 2016, and for interim periods within annual periods ending after December 15, 2016. The Company has adopted ASU 2014-15, which did not have a material effect on the Company's consolidated financial statements. In November 2015, the FASB issued ASU No. 2015-17, Balance Sheet Classification of Deferred Taxes ("ASU 2015-17"). To simplify presentation, the new guidance requires that all deferred tax assets and liabilities, along with any related valuation allowance, be classified as noncurrent on the balance sheet. As a result, each jurisdiction will now only have one net noncurrent deferred tax asset or liability. ASU 2015-17 is effective for public business entities in fiscal years beginning after December 15, 2016, including interim periods within those years. Early adoption is permitted for all entities as of the beginning of an interim or annual reporting period. The Company is evaluating the adoption of ASU 2015-17, but has not determined the effects it may have on the Company's consolidated financial statements. In February 2016, the FASB issued Accounting Standards Codification ("ASC") No. 2016-02, Leases ("ASC 842"). The guidance requires lessees to recognize almost all leases on their balance sheet as a right-of-use asset and a lease liability. For income statement purposes, the FASB retained a dual model, requiring leases to be classified as either operating or finance. Lessor accounting is similar to the current model, but updated to align with certain changes to the lessee model and the new revenue recognition standard. Existing sale-leaseback guidance, including guidance for real estate, is replaced with a new model applicable to both lessees and lessors. ASC 842 is effective for fiscal years beginning after December 15, 2018. The Company is evaluating the adoption of ASC 842, but has not determined the effects it may have on the Company's consolidated financial statements. In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting ("ASU 2016-09"), which requires the Company to recognize the income tax effects of awards in the income statement when the awards vest or are settled. ASU 2016-09 is effective for annual and interim periods beginning after December 15, 2016, with early adoption permitted. The Company has adopted ASU 2016-09, which did not have a material effect on the Company's consolidated financial statements. In August 2016, the FASB issued Accounting Standards Update, or ASU, 2016-15, Statement of Cash Flows (Topic 230). ASU 2016-15 is intended to reduce the diversity in practice regarding how certain transactions are classified within the statement of cash flows. ASU 2016-15 is effective for public business entities for annual periods beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted with retrospective application. The Company is evaluating the adoption of ASU 2016-15, but has not determined the effects it may have on the Company's consolidated financial statements.
Deferred Initial Public Offering Costs	Deferred Initial Public Offering Costs Deferred initial public offering costs, which primarily consist of direct, incremental legal, accounting and other professional fees relating to the IPO, are included in other long-term assets in the consolidated balance sheet as of December 31, 2015. These deferred costs were offset against the IPO proceeds upon the consummation of the offering. As of December 31, 2016 and 2015, the Company deferred $0 and $1,624,040 of IPO-related costs.