* Says delays launch of Down Syndrome test

* Cites employee mishandling

* Shares plunge 70 percent after the bell (Adds conference calls details, updates share movement)

April 29 (Reuters) - Sequenom Inc (SQNM.O: Quote, Profile, Research) said employee mishandling of research and development test data and results has forced it to delay the launch of a Down Syndrome test, sending its shares plunging 70 percent.

The maker of genetic analysis products said it is no longer relying on previously announced research and development test data and results related to its SEQureDx technology.

Sequenom's SEQureDx tests the DNA of a foetus from a mother's blood in a non-invasive manner to see if the blood groups of the mother and the child are compatible.

The company said its board has formed a special committee of independent directors to oversee an independent investigation of the employees' activity related to the test data and results.

However, Sequenom also said its SEQureDx technology remained scientifically and technically sound. It said the company has not changed its plans to develop in parallel its RNA- and DNA-based methods for the Down Syndrome test and will endeavor to have a validated test in the fourth quarter of 2009.

"We are not back at square one. We have a lot of information and see virtue in both assay technologies," Sequenom's Chief Executive Harry Stylli said on a conference call.