EXHIBIT 6

Joint Filing Agreement, dated April 11, 2013

PURSUANT TO RULE 13d-1(k)

The undersigned acknowledge and agree that the foregoing statement on Schedule 13D is filed on behalf of each of the undersigned and that all subsequent amendments to this statement on Schedule 13D may be filed on behalf of each of the undersigned without the necessity of filing additional joint filing agreements. The undersigned acknowledge that each shall be responsible for the timely filing of such amendments, and for the completeness and accuracy of the information concerning it contained herein and therein, but shall not be responsible for the completeness and accuracy of the information concerning the others, except to the extent that it knows that such information is inaccurate.

Dated: April 11, 2013.

First manhattan co.

By first manhattan llc, General Partner

By:  /s/ Neal K. Stearns

Name: Neal K. Stearns

Title:   Managing Member

FIRST BIOMED MANAGEMENT ASSOCIATES, LLC

By FIRST MANHATTAN CO., Co-Managing Member

By FIRST MANHATTAN LLC, General Partner

By: /s/ Neal K. Stearns

Name: Neal K. Stearns

Title: Managing Member

By: /s/ Herman Rosenman

Herman Rosenman