DNA Pairing - Arrow function not working

JavaScript
1

I currently have this answer that works fine

function pairElement(str) {
  let dnaStr = [];
  dnaStr = str.split('').map( function(x) {
    switch(x) {
      case 'A': return ['A','T'];
      break;

      case 'T': return ['T','A'];
      break;

      case 'C': return ['C','G'];
      break;

      case 'G': return ['G','C'];
      break;

    };
  });
  return dnaStr;
}

pairElement("ATCGA");

Why does this not work if i change the function within the map argument to an arrow function format like this:

function pairElement(str) {
  let dnaStr = [];
  dnaStr = str.split('').map( x =>  (
    switch(x) {
      case 'A': return ['A','T'];
      break;

      case 'T': return ['T','A'];
      break;

      case 'C': return ['C','G'];
      break;

      case 'G': return ['G','C'];
      break;

    };
  ));
  return dnaStr;
}

pairElement("ATCGA");

I get a syntax error. Why does the arrow function format not work. Have i written that incorrectly?

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Link to the challenge:
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/dna-pairing