Apple shares slide on news of Steve Jobs&39' medical leave of absence.

Apple's shares are trading lower this morning as investors start to come to grips with the news of Steve Jobs taking his second medical leave of absence in two years.

An hour and a half into morning activity on the Nasdaq exchange, Apple shares were down approximately $13 to just over $335 per share, representing a nearly 4 percent slide.

Apple released word of Jobs' medical leave early yesterday on the federal holiday honoring Martin Luther King Jr., meaning that the stock market was closed. That extra day to process the news likely softened the reaction on Wall Street over worries about how Apple will fare in the day-to-day absence of its CEO, a pancreatic cancer survivor.

The reaction also may be tempered by expectation of more favorable news later today when Apple is scheduled to announce its fiscal first-quarter earnings, which includes the holiday sales period. Financial analysts are expecting a strong showing, with average forecast for revenue coming in at $24.38 billion and earnings per share at $5.38.

Apple gave no date for Jobs' return, but said that Jobs would continue to have a say in strategic decisions. In his absence, day-to-day operations will be handled by Chief Operating Officer Tim Cook, who also filled in during Jobs' 2009 medical leave.