For readers with dyslexia, a common symptom is the rotation and transposition of letters. A lowercase b is sometimes mistaken as a lowercase d. This problem does not happen when using uppercase versions of the same letters, because an uppercase B does not resemble an uppercase D visually. Lowercase p is sometimes seen as a lowercase q. Also, dyslexics can rotate the letters vertically, so a p can become a d or a b.
In 2014, Dutch designer Christian Boer invented a new typeface for readers with dyslexia called Dyslexie that adapts to the problems listed above by making the letters of the dyslexic alphabet unique. The letters are designed to be heavier at the bottom, to prevent readers with dyslexia and writers with dyslexia from flipping the letters vertically. Since the letters are wider at the bottom, it’s more difficult to misinterpret a letter that is wide at the top–a dyslexic knows immediately that the letter is upside down.
Other tweaks include making letters like i and j (often switched for dyslexics) have been altered so that j appears with a slight tilt while i remains perpendicular. There’s more to the science behind Dyslexie’s design, which Christian Boer covers in detail (with examples and images) in the TED talk below: