OF ALL THE WRINKLES in the emerging measles crisis and spotlight it has put on families who have caused the outbreak by refusing to vaccinate their children, the most curious has been the leading role of Robert F. Kennedy, Jr.

The third child and namesake of Robert Kennedy has spent years promoting the debunked idea that vaccines can cause autism in children. He has fanned the flames of conspiracy theorists and true-believers of assorted wacky claims to provide justification for the anti-vaxxer movement that shuns immunizations.

While Kennedy has been roundly criticized for years by leading voices in medicine and public health, his views come in for a harsh rebuke today from three people who know him well — two of his siblings and a niece who directs an initiative on global health. Kathleen Kennedy Townsend, Joseph P. Kennedy II, and Maeve Kennedy McKean pen a commentary piece for Politico ripping Robert Kennedy Jr.’s role in stirring the anti-vaccine movement.

The surge of measles cases in the US — over 700 cases so far — and the more than 100,000 annual deaths globally from the disease “are caused by the growing fear and mistrust of vaccines—amplified by internet doomsayers,” they write. Their brother and uncle, write the trio, “is part of this campaign to attack the institutions committed to reducing the tragedy of preventable infectious diseases. He has helped to spread dangerous misinformation over social media and is complicit in sowing distrust of the science behind vaccines.”

Kennedy’s leading role with the anti-vaxxer wing of the tinfoil hat brigade is sharply at odds with his family’s legacy of landmark work on behalf of mainstream medicine and public health, including efforts to bring life-saving vaccines to the most remote parts of the world.

The three family members recount President Kennedy, in 1961, urging Americans to receive the groundbreaking Salk vaccine against polio — “this miraculous drug,” the president proclaimed. Kennedy also signed the order creating the US Agency for International Development, which has spent billions of dollars bringing vaccines to developing countries, and signed the Vaccination Assistance Act in 1962, which helped bring immunizations to all Americans, especially young children. Ted Kennedy, too, they write, left an enormous legacy in support of health care issues, including vaccination efforts.

“On this issue, Bobby is an outlier in the Kennedy family,” they write.

President Trump has been among those who have given credence to the anti-vaccine movement, raising the issue of a link between vaccines and autism in a 2015 debate. After his election, Trump met with Kennedy and there was talk of RFK, Jr. heading a commission to study vaccine safety. But Kennedy said recently that he’s been shut out by the administration, which has not taken any steps to form such a panel.

This 2017 Q&A with STAT offers a revealing look at Kennedy’s views, and the difficulty of even getting him to agree on a basic set of facts on which to base a conversation on vaccine safety. Writer Seth Mnookin, author of a book on “the myth” that vaccines can cause autism, titled his chapter on Kennedy’s efforts, “A Conspiracy of Dunces.”

A Globe editorial today sounds the alarm on measles in Massachusetts, where at least 60 suspected cases have been reported, urging the Legislature to eliminate or narrow religious exemptions from vaccination requirements and allow teenagers to seek vaccines on their own if their families have shunned the practice.

“It’s flabbergasting that a preventable disease like measles is back, and that state legislatures have been as slow as the rest of us to wake up to a threat that shouldn’t be happening at all,” says the editorial. “But it is happening.”