Cystic fibrosis is caused by the inheritance of two copies of a defective gene, one from each parent.

He points to two areas where information is publicly available: heart surgery by the Society of Thoracic Surgeons and cystic fibrosis.

Bar-Or stresses that none of these MS-associated variants is abnormal — they are not 'disease genes' like the mutations that cause cystic fibrosis, for example.