KNOW IT ALL: Monday's Top Stories at NBC News

In this Tuesday, April 26, 2016 photo, an Aedes aegypti mosquito is seen through a microscope at Colombia's National Institute of Health in Bogota, Colombia. Margaret Honein, of the Centers for Disease Control and Prevention, CDC, said that apart from microcephaly, babies whose mothers have had Zika during pregnancy may eventually acquire impaired hearing or vision.Fernando Vergara / AP

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Good morning. Here are some of the stories we're following today:

1. Zika Virus Birth Defects May Be 'Tip of the Iceberg'

The explosion of cases of birth defects caused by Zika virus may be the "tip of the iceberg," experts said Sunday. Many cases have probably been missed because babies looked normal when they were born. But hidden birth defects are almost certain to turn up as the babies grow, they told a meeting of pediatricians Sunday in Baltimore. Read more in HEALTH.

2. Sanders Insists He Can Still Win Nomination

Facing a large delegate deficit, tough odds and just 10 remaining state contests, Senator Bernie Sanders made it clear Sunday that he intends to fight on to become the Democratic presidential nominee. Sanders' stated path relies on primary opponent Hillary Clinton not reaching a majority of pledged delegates and on superdelegates switching their allegiances. Read more in POLITICS.

3. Seattle May Day March Turned Violent

At least nine protesters were arrested and five police officers injured during May Day clashes in Seattle where flares, bricks and Molotov cocktails were thrown, authorities said. The anti-capitalist disorder followed a peaceful march earlier in the day by advocates for workers and immigrants — one of several nationwide events Sunday calling for better wages for workers and work permits for undocumented migrants. Read more in NEWS.

4. Puerto Rico to Default on $422 Million Debt Payment

Crushed by rampant joblessness and poverty and hemorrhaging educated residents, Puerto Rico will default on $422 million in debt payments due Monday, Gov. Alejandro García Padilla said Sunday. García said in a televised address that the failure of negotiations to reach a last-minute deal to avoid a third default forced his hand. Read more in NEWS.

5. No Water, No Teachers for Detroit

A year and a half after the city emerged from the largest municipal bankruptcy in U.S. history, Detroit 2.0 is still beset by crippling bugs in the system. As early as Monday, the city's Department of Water and Sewerage is prepared to begin shutting off the water to 23,000 commercial and residential customers who've defaulted on their payments. Meanwhile, the school system is running out of money and will have to stop paying teachers and staff on June 30. Read more in NEWS.

6. L.A. Sheriff's Official Resigns Over Racist Emails

Tom Angel resigned from his position as the Los Angeles County sheriff's chief of staff Sunday after it was discovered he sent racist emails while he was an assistant police chief elsewhere. The emails, sent in 2012 and 2013, made offensive references to blacks, Muslims, Latinos and others. Read more at NBC LOS ANGELES.

7. Malia Obama to Attend Harvard University

President Barack Obama's oldest daughter is going to Harvard. Malia Obama will attend the elite Ivy League school in the fall of 2017, the president and first lady said in a statement on Sunday. The 17-year-old will be taking a "gap year" before attending the university, the White House statement said. It was unclear what Malia will be doing in her year off. "Gap years" are often used to travel the world and/or do humanitarian work. Read more in NEWS.

Nightly Spotlight: The Sweet Taste of Success Running an Ice Cream Parlor

A lawyer who worked in the Obama administration but also likes making ice cream is finding success with her new business venture.