Income taxes	6 Months Ended
Jun. 30, 2018
Income taxes
Income taxes	9. Income taxes Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, including its net operating losses. Based on its history of operating losses, the Company believes that it is more likely than not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of June 30, 2018 and December 31, 2017. On December 22, 2017, the President of the United States signed into law the Tax Cuts and Jobs Act (“TCJA”). The TCJA makes significant changes in U.S. tax law including a reduction in the corporate tax rates, changes to net operating loss carryforwards and carrybacks, and a reduction of the amount of the orphan drug credit. As a result of the TCJA, the Company remeasured its ending deferred tax assets and liabilities at December 31, 2017 to the newly enacted U.S. federal corporate tax rate of 21%. The Company recognized the provisional tax impacts related to the remeasurement of the deferred tax assets and liabilities pursuant to SEC Staff Accounting Bulletin No. 118 and included these amounts in its financial statements for the year ended December 31, 2017. The Company did not record any adjustments to this provisional amount during the period ended June 30, 2018 and will continue to analyze and refine its calculations related to the remeasurement as the impact of TCJA is finalized.

9. Income taxes

Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, including its net operating losses. Based on its history of operating losses, the Company believes that it is more likely than not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of June 30, 2018 and December 31, 2017.

On December 22, 2017, the President of the United States signed into law the Tax Cuts and Jobs Act (“TCJA”). The TCJA makes significant changes in U.S. tax law including a reduction in the corporate tax rates, changes to net operating loss carryforwards and carrybacks, and a reduction of the amount of the orphan drug credit. As a result of the TCJA, the Company remeasured its ending deferred tax assets and liabilities at December 31, 2017 to the newly enacted U.S. federal corporate tax rate of 21%. The Company recognized the provisional tax impacts related to the remeasurement of the deferred tax assets and liabilities pursuant to SEC Staff Accounting Bulletin No. 118 and included these amounts in its financial statements for the year ended December 31, 2017. The Company did not record any adjustments to this provisional amount during the period ended June 30, 2018 and will continue to analyze and refine its calculations related to the remeasurement as the impact of TCJA is finalized.