In an interview with the UK Guardian, Michael Douglas revealed that his 10 year old son, Dylan, has dyslexia and that it "runs in the family" (Michael's brother has it). Michael and his family recently relocated to New York so Dylan could attend a special school to assist him.
Dyslexia can produce any number of challenges that are mostly focused around reading, writing, and speaking, so it tends to be Mercury's terrain. The condition of Mercury in a natal chart indicates how we'll think and process information, communicate, and the way our mind works in general, both symbolically and literally to some extent.
Dylan's Mercury is in Leo in the 7th house of his chart, not necessarily indicative of any learning disabilities. Any planet in a sign or house alone can manifest a number of ways. Aspects between planets typically show more of the action and dynamic qualities of a chart, so any tension or difficulty a planet is under is often more easily seen in its connections to other planets.
In Dylan's case, his Mercury is conjunct Mars, indicating that a lot of passion, fire, and energy is running through his mental circuits. He may find himself wanting to respond quickly or off the cuff, almost as if his mind and mouth are running faster than he is. Someone with this configuration might simply talk very quickly, so we wouldn't see dyslexia in even the majority of the cases, but where we know it's present, we might suspect that the nature of the Mercurial challenge in Dylan's case is an issue of speed, as in, too much of it. Mars can also illustrate where people hold their stress and anxiety in general, where burnout or overwhelm can happen if stress levels get too high, and it's said that both stress and anxiety can exacerbate dyslexia symptoms (although there's precious little in this world that stress and anxiety don't worsen!)
Dylan also has Neptune in Aquarius opposed his Mercury and Mars. Dyslexia has no bearing on intelligence or vice versa: it is simply a matter of how information is processed and communicated, not whether it's understood on a conceptual level. Neptune has an 'other-worldly' quality to it; it represents the part of us that is least attached to the logical, 3-dimensional, shared 'reality' world and more connected to things like the dream world (waking or sleeping), intuition, imagination, and the part of us that understands symbols and metaphors. Neptune is often thought to have a 'foggy' influence on life, but that is only when we are trying to rigidly define our world. In our imagination or our dream world, we would have no problem saying 2+2=22 if it made a kind of creative sense to us, for instance. With Neptune in a difficult relationship to Mercury, he processes messages in a way that is outside the rigid rules of '2+2=4 and nothing else' thinking. His mind is free, for better and worse, to process information outside of typical constraints.
Something that can help him master and manage symptoms of dyslexia is his Saturn in Taurus, in a sextile relationship to Mercury, indicating that Saturn and Mercury can work well together. Slowing it down (Taurus) and steady practice (Saturn) are his best tools, but he'll also benefit from finding ways to incorporate the imagination and symbolism of his Neptune into his mental processes in a way that doesn't just lead to confusion, but a new way of looking at things entirely! Inventive and imaginative greats such as Leonardo da Vinci, Thomas Edison, and Mozart were all said to have some form of dyslexia.