---

---

Exhibit 10.50a

Certain confidential information
contained in this document, marked by brackets and the word Redacted
([REDACTED]), has been omitted and filed separately with the Securities and Exchange
Commission pursuant to Rule 24b-2 promulgated under the Securities Exchange Act of 1934,
as amended.

December 22, 2004

Dennis A. Rossi
Senior Vice President, General Manager, Genomics Gene Logic Inc.
610 Professional DriveGaithersburg, MD 20879

| | Re: | Letter
Agreement ("Letter Agreement") amending the terms of the Amended and Restated Agreement
entered into by and between Gene Logic Inc. ("Gene Logic") and Affymetrix, Inc.
("Affymetrix") effective January 1, 2002, as amended ("Agreement")
| | --- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Dear Mr. Rossi:

By entering into this Letter
Agreement, Gene Logic and Affymetrix hereby agree to amend the Agreement as follows:

|1. | Revise
section 2.29 to read:
|-- | ----------------------------

| | 2.29
Temporary Period shall mean the period commencing on July 1, 2003 and
continuing through December 31, 2005.
| | ------------------------------------------------------------------------------------------------------------------

|2. | The
Price List attached as Exhibit I-1 to the amendment dated September 23,
               2003, as amended by the letter dated April 4, 2004, shall continue to
apply to                orders placed during the remaining portion of the Temporary
Period. For                convenience, a copy of such Price List is attached hereto as
Exhibit A.
|-- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|3. | After
Section 5.1, insert new sections 5.1.1 through 5.1.4 as follows:
|-- | ----------------------------------------------------------------------

| | 5.1.1.       
 Notwithstanding
Section 5.1 above and in lieu of the annual payment of                     $4,000,000 for
2005 otherwise required thereby, during the period commencing on
                    January 1, 2005, and continuing through December 31, 2005, Gene Logic
shall pay                     to Affymetrix a fee of $500,000, payable in $125,000
increments due at the end                     of each calendar quarter during such
period.
| | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | 5.1.2.       
Gene
Logic agrees to purchase the following products at the following prices,
                    to be shipped to the address set forth above by Affymetrix on or
before December                     31, 2004. Such purchase shall not count toward Gene
Logics 2005 purchase                     commitment described in Section 5.1.3
below.
| | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|Description                      | Quantity   | Unit price*       | Subtotal** 
|-------------------------------- | ---------- | ----------------- | -----------
|Human Genome U133 2.0 Plus array | [REDACTED] | $[REDACTED]/array | $[REDACTED]
|IVT kits                         | [REDACTED] | $[REDACTED]/kit   | $[REDACTED]
|Rat Genome 230 2.0 arrays        | [REDACTED] | $[REDACTED]/array | $[REDACTED]
|TOTAL PRICE**: $500,080         

| | *Theseprices
do not include use for Services or Tox Services; if such products are intended for use,
or are used, for Services or Tox Services, the pricing in Exhibit I-1 (as amended) shall
apply instead.
| | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | **Excludes
freight and handling.
| | --------------------------------

Page 1 of 4

---

---



| | 5.1.3.       
                     Gene
Logic agrees to purchase $9,500,000 worth of Probe Arrays, reagents,
                    services under maintenance and service agreements and/or
instrumentation during                     the period commencing on January 1, 2005, and
continuing through December 31,                     2005, to be shipped (or in the case
of services to be provided) by Affymetrix on                     or before December 31,
2005. Probe Arrays purchased for database                     upgrades/re-runs and priced
at the volume discount upgrade\re-run pricing                     attached hereto as
Exhibit B shall count toward such purchase commitment. If                     Gene Logic
fails to purchase such amount of such products by December 31, 2005
                    (for shipment within 2005), then Gene Logic shall pay upon receipt of
                    Affymetrix invoice the difference between $9,500,000 and the
amount of                     such purchases actually made by Gene Logic in 2005.
| | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | 5.1.4.       
                  Gene
Logic agrees to purchase one GeneChip Array Station for $[REDACTED]and one
                    GeneChipHT array scanner for $[REDACTED] (such prices exclude freight
and                     handling) during the period commencing on January 1, 2005, and
continuing                     through December 31, 2005, for shipment by Affymetrix on
or before December 31,                     2005. Such purchases shall count toward Gene
Logics 2005 purchase                     commitment described in Section 5.1.3
above.
| | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Unless otherwise modified herein, all
capitalized terms used in this letter shall have the meaning ascribed to them in the
Agreement. All other aspects of the Agreement remain unchanged and in full force and
effect.

AGREED AND ACKNOWLEDGED:

|Affymetrix, Inc.BY: /S/ Barbara A Caulfield
Name: Barbara A. CaulfieldTitle: Executive Vice President and General CounselDate: December 22, 2004 | Gene Logic Inc.BY: /S/ Dennis A. Rossi
Name: Dennis RossTitle: Senior Vice President and General           Manager, Genomics Business UnitDate: December 22, 2004
|-------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Page 2 of 4

---

---



Exhibit A Temporary Period Price List Standard Probe ArraysPer array pricing in US Dollars

|                                                             |                                      | A               | B                                   
|------------------------------------------------------------ | ------------------------------------ | --------------- | ------------------------------------
|Part Number                                                  | Array Name                           | StandardPricing | Service Provider Supplemental Charge
|Human Array                                                  |                                      |                 |                                     
|900466,900467900470                                          | Human Genome U133 2.0 Plus           | [REDACTED]      | [REDACTED]                          
|900468, 900469900471                                         | Human Genome U133A 2.0               | [REDACTED]      | [REDACTED]                          
|900366, 900367, 900368,900369, 900370, 900444 510681, 510682 | Human Genome U133A or U133Barray     | [REDACTED]      | [REDACTED]                          
|900303, 900304                                               | Human GenomeU95Av2 Array             | [REDACTED]      | [REDACTED]                          
|900376, 900377                                               | Human Genome Focus Array             | [REDACTED]      | [REDACTED]                          
|                                                             |                                      |                 |                                     
|Rat Array                                                    |                                      |                 |                                     
|900505, 900506, 900507                                       | Rat Genome 230 2.0                   | [REDACTED]      | [REDACTED]                          
|900404, 900405, 900406,900407, 900408, 900442                | Rat Expression Array 230A or 230B    | [REDACTED]      | [REDACTED]                          
|900249, 900286510338                                         | Rat Genome U34A Array                | [REDACTED]      | [REDACTED]                          
|900250, 900251, 900287, 900288510339, 510340                 | Rat Genome U34B or U34CArray         | [REDACTED]      | [REDACTED]                          
|                                                             |                                      |                 |                                     
|Mouse Array                                                  |                                      |                 |                                     
|900495, 900496 900497                                        | Mouse Genome 430 2.0                 | [REDACTED]      | [REDACTED]                          
|900498, 900499900500                                         | Mouse Genome 430A 2.0                | [REDACTED]      | [REDACTED]                          
|900412, 900413, 900414,900415, 900416, 900443                | Mouse Expression Array 430Aor 430B   | [REDACTED]      | [REDACTED]                          
|900343, 900344510568                                         | Murine Genome U74Av2 Array           | [REDACTED]      | [REDACTED]                          
|900357, 900358, 900359, 900360510570, 510571                 | Murine Genome U74Bv2 or U74Cv2 Array | [REDACTED]      | [REDACTED]                          
|                                                             |                                      |                 |                                     
|900489, 900490                                               | Canine                               | [REDACTED]      | [REDACTED]                          
|                                                             |                                      |                 |                                     
|520049                                                       | Human X3P                            | [REDACTED]      | [REDACTED]                          
|                                                             |                                      |                 |                                     
|900487, 900488                                               | Zebrafish                            | [REDACTED]      | [REDACTED]                          
|                                                             |                                      |                 |                                     
|900491, 900492                                               | Xenopus                              | [REDACTED]      | [REDACTED]                          
|                                                             |                                      |                 |                                     
|Customexpress Array                                          |                                      |                 |                                     
|510685                                                       | Canine Array                         | [REDACTED]      | [REDACTED]                          

Page 3 of 4

---

---



Exhibit B
Database upgrade/re-run pricing

|                                               | New Samples | Database Upgrade/Rerun
|---------------------------------------------- | ----------- | ----------------------
|
|
|Cartridge Arrays                               |             |                       
|Human Genome U133 2.0 Plus                     | $[REDACTED] | $[REDACTED]           
|Rat Genome 230 2.0                             | $[REDACTED] | $[REDACTED]           
|Mouse Genome 430 2.0                           | $[REDACTED] | $[REDACTED]           
|HTA Peg Arrays                                 |             |                       
|Total Peg Arrays and Reagents (Price Per Well) | $[REDACTED] | $[REDACTED]           

For accounting purposes, Gene Logic
needs to notify Affymetrix by January 15, 2005, which volume bracket Gene Logic is
committing to for database upgrade/re-runs for 2005. Gene Logic shall indicate on its
purchase orders which Probe Arrays will be used for database upgrades/re-runs.

Page 4 of 4

---

---