19:I[66739,["/_next/static/chunks/0.3dg.jzl0xwf.js?dpl=dpl_BhmHa8NmNRnoMAUm8Lqp3TPz2qZA","/_next/static/chunks/0qxr~fpya2kw0.js?dpl=dpl_BhmHa8NmNRnoMAUm8Lqp3TPz2qZA","/_next/static/chunks/12wfgjmhh21qu.js?dpl=dpl_BhmHa8NmNRnoMAUm8Lqp3TPz2qZA","/_next/static/chunks/028~snn2srcd-.js?dpl=dpl_BhmHa8NmNRnoMAUm8Lqp3TPz2qZA","/_next/static/chunks/079qbl7l5rd72.js?dpl=dpl_BhmHa8NmNRnoMAUm8Lqp3TPz2qZA","/_next/static/chunks/0hi8o2xq05aig.js?dpl=dpl_BhmHa8NmNRnoMAUm8Lqp3TPz2qZA"],"default"] 1b:I[38632,["/_next/static/chunks/0qqtp3r0h7kah.js?dpl=dpl_BhmHa8NmNRnoMAUm8Lqp3TPz2qZA","/_next/static/chunks/0iukvycbd42rl.js?dpl=dpl_BhmHa8NmNRnoMAUm8Lqp3TPz2qZA"],"IconMark"] 1a:T455,Sam and John Fetters, 19, are identical twins on different ends of the autism spectrum. Sam is a sophomore at Amherst College and runs marathons in his free time. John attends a school for people with special needs and loves to watch Sesame Street in his free time. Identical twins like Sam and John pose an important question for scientists: How can a disorder that is known to be highly genetic look so different in siblings who share the same genome?

Check out more of NPR's series on the Science of Siblings.

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How Autism Can Look Very Different, Even in Identical Twins

Short Wave

How Autism Can Look Very Different, Even in Identical Twins