SECURITIES AND EXCHANGE COMMISSION
                             Washington, D. C. 20549

                                  SCHEDULE 13G

                    Under the Securities Exchange Act of 1934

                          ALNYLAM PHARMACEUTICALS, INC.
                          -----------------------------
                                (Name of Issuer)

                     Common Stock, $.01 par value per share
                     --------------------------------------
                         (Title and Class of Securities)

                                    02043Q107
                                    ---------   
                                 (CUSIP Number)

                                 April 12, 2007
                                 --------------
             (Date of Event which Requires Filing of this Statement)

Check the  appropriate box to designate the rule pursuant to which this schedule
is filed:

      [x] Rule 13d-1(b)
      [ ] Rule 13d-1(c)
      [ ] Rule 13d-1(d)

* The remainder of this cover page shall be filled out for a reporting  person's
initial filing on this form with respect to the subject class of securities, and
for any  subsequent  amendment  containing  information  which  would  alter the
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the  Securities  Exchange  Act of
1934 (the "Act") or otherwise  subject to the liabilities of that section of the
Act but shall be subject to all other  provisions of the Act  (however,  see the
Notes).


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CUSIP No. 02043Q107                                            Page 2 of 6 Pages
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      1     NAMES OF REPORTING PERSONS
            S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

            ALETHEIA RESEARCH AND MANAGEMENT, INC., IRS number 95-4647814, as
            general partner of various limited partnerships and on behalf of
            various managed accounts.

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      2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP          (a) [ ]
                                                                      (b) [ ]

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      3     SEC USE ONLY

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      4     CITIZENSHIP OR PLACE OF ORGANIZATION

            California

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                                    5     SOLE VOTING POWER

                                          2,443,996

        NUMBER OF         ------------------------------------------------------
         SHARES                     6     SHARED VOTING POWER
      BENEFICIALLY
        OWNED BY                          0
          EACH    
        REPORTING         ------------------------------------------------------
         PERSON                     7     SOLE DISPOSITIVE POWER
          WITH    
                                          2,443,996

                          ------------------------------------------------------
                                    8     SHARED DISPOSITIVE POWER

                                          0

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      9     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

            2,443,996

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      10    CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN
            SHARES*                                                       [ ] 

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      11    PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

            6.51%

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      12    TYPE OF REPORTING PERSON*

            Aletheia Research and Management, Inc.- IA

--------------------------------------------------------------------------------

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CUSIP No. 02043Q107                                            Page 3 of 6 Pages
-------------------                                            -----------------

Item 1(a).     Name of Issuer:

               Alnylam Pharmaceuticals, Inc.

Item 1(b).     Address of Issuer's Principal Executive Offices:

               300 Third Street, Cambridge, MA 02142

Item 2(a).     Name of Person Filing:

               Aletheia Research and Management, Inc.

Item 2(b).     Address of Principal Business Office or, if None, Residence:

               100 Wilshire Boulevard, Suite 1960, Santa Monica, CA 90401

Item 2(c).     Citizenship:

               Not Applicable.

Item 2(d).     Title of Class of Securities:

               Common Stock, $.01 par value.

Item 2(e).     CUSIP Number:

               02043Q107

Item 3.        If this statement is filed pursuant to Rule 13d-1(b), or 13d-2(b)
               or (c), check whether the person filing is a:

           (a) [ ] Broker or Dealer registered under Section 15 of the Act.

           (b) [ ] Bank as defined in Section 3(a)(6) of the Act.

           (c) [ ] Insurance Company as defined in Section 3(a)(19) of the Act.

           (d) [ ] Investment Company registered under Section 8 of the
                   Investment Company Act.

           (e) [X] Investment Adviser registered in accordance with Rule
                   13d-1(b)(1)(ii)(E).

                                        3


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CUSIP No. 02043Q107                                            Page 4 of 6 Pages
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           (f) [ ] Employee Benefit Plan or Endowment Fund in accordance with
                   Rule 13d-1(b)(1)(ii)(F).

           (g) [ ] Parent Holding Company or control person in accordance with
                   Rule 13d-1(b)(1)(ii)(G).

           (h) [ ] A savings association as defined in Section 3(b) of the
                   Federal Deposit Insurance Act.

           (i) [ ] A church plan that is excluded from the definition of an
                   investment company under Section 3(c) (14) of the Investment 
                   Company Act of 1940.

           (j) [ ] Group, in accordance with Rule 13d-1(b)(1)(ii)(J).

                   If this Statement is filed pursuant to Rule 13d-1(c), check 
                   this box [ ].

Item 4.        Ownership.

                   (a) Amount beneficially owned: 2,443,996*

                   (b) Percent of Class:          6.51%

                   (c) Number of Shares as to which the person has:

                         (i)   Sole power to vote or to direct the vote: 
                               2,443,996

                         (ii)  Shared power to vote or to direct the vote: 0

                         (iii) Sole power to dispose or to direct the
                               disposition of: 2,443,996

                         (iv)  Shared Power to dispose or to direct the
                               disposition of: 0

                   * See Disclaimer of Beneficial Ownership

Item 5.        Ownership of Five Percent or Less of a Class.

            If this statement is being filed to report the fact that as of the
date hereof the reporting person has ceased to be the beneficial owner of more
than five percent of the class of securities, check the following. [ ].

Item 6         Ownership of More than Five Percent on Behalf of Another Person.

               Various accounts and funds managed by the reporting person have
               the right to receive or the power to direct the receipt of
               dividends from, or the proceeds from the sale of, the securities
               held in their respective accounts. To the knowledge of the
               reporting person, the interest of any one such account does not
               exceed 5% of the class of securities.

Item 7.        Identification and Classification of the Subsidiary Which
               Acquired the Security Being Reported on by the Parent Holding
               Company.

               Not Applicable.

                                        4


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CUSIP No. 02043Q107                                            Page 5 of 6 Pages
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Item 8.        Identification and Classification of Members of the Group.

               Not Applicable

Item 9.        Notice of Dissolution of Group.

               Not Applicable.

Item 10.       Certification.

               By signing below, I certify that, to the best of my knowledge and
               belief, the securities referred to above were not acquired and
               are not held for the purpose of or with the effect of changing or
               influencing the control of the issuer of the securities and were
               not acquired and are not held in connection with or as a
               participant in any transaction having that purpose or effect.

                                    SIGNATURE

Date: June 6, 2007           ALETHEIA RESEARCH AND MANAGEMENT, INC.,

                                        By: /s/ Roger Peikin
                                            ----------------
                                            Name: Roger Peikin
                                            Title: Executive Vice-President

                                        5


<PAGE>

                                                                       EXHIBIT A

                       DISCLAIMER OF BENEFICIAL OWNERSHIP

Alnylam Pharmaceuticals, Inc.
Common Stock
2,443,996 shares

Aletheia  Research and Management,  Inc.  ("Aletheia") is an investment  advisor
registered  under Section 203 of the Investment  Advisors Act of 1940 and serves
in such capacity for a number of managed  accounts and funds.  In its role as an
investment advisor or manager, Aletheia possesses investment and/or voting power
over the securities of the Issuer discussed in this schedule. Aletheia disclaims
beneficial  ownership  of such  securities.  In  addition,  the  filing  of this
Schedule 13G shall not be construed as an admission that the reporting person or
any of its affiliates is the beneficial owner of any securities  covered by this
Schedule  13G for any  purposes  other  than  Section  13(a)  of the  Securities
Exchange Act of 1934.

                                        6