A top executive who helped build Theranos Inc. into a major blood-testing laboratory is leaving the company amid regulatory probes of the embattled Silicon Valley firm.

The departure of Sunny Balwani as Theranos president and chief operating officer comes amid a broader board reorganization announced by the Palo Alto, Calif., firm. In a release late Wednesday, Theranos said it is expanding its board, adding three members to beef up its scientific and medical expertise.

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