SCHEDULE 13G/A

Alector Inc

Common Stock, $0.0001 par value per share · CUSIP: 014442107

Event date: 2025-09-30

Reporting persons may disclose overlapping interests. Their amounts are shown individually and are not added into a filing total.

Filing-level shares

Unavailable

Percent of class

Unavailable

• Polaris Venture Partners VI, L.P.

  Shares: 498,468 · Class: 0.5%

• Polaris Venture Partners Founders' Fund VI, L.P.

  Shares: 378,403 · Class: 0.3%

• Polaris Venture Partners VI (AIV), L.P.

  Shares: 4,797,563 · Class: 4.4%

• Polaris Venture Partners VI (AIV-B), L.P.

  Shares: 1,179,383 · Class: 1.1%

• Polaris Venture Management Co VI, L.L.C.

  Shares: 6,853,817 · Class: 6.3%

• David Barrett

  Shares: 6,880,071 · Class: 6.3%

• Brian Chee

  Shares: 6,880,084 · Class: 6.3%

• Jonathan A. Flint

  Shares: 6,892,942 · Class: 6.3%

• Terrance G. McGuire

  Shares: 7,095,251 · Class: 6.5%

• Amir Nashat

  Shares: 6,932,617 · Class: 6.4%

• Bryce Youngren

  Shares: 6,945,149 · Class: 6.4%

Amounts are as disclosed in this filing. Schedule type alone does not establish investment intent.