The simplest analogy I can provide for this is one from medicine. If you showed up at your doctor's office with a broken leg and pneumonia, would the doctor choose to treat the pneumonia but not set the broken leg? Of course not! Both conditions merit treatment, and both dyslexia and giftedness require intervention as well.
Do contact your school about having your youngest child tested. At that time, ask to make an appointment with the psychologist or other professional doing the testing. (In some schools, the counselor coordinates testing.) Share your family history and indicate that you believe this child may be both gifted and dyslexic, and that, if so, you would like to see him receive services for both issues. Once the testing is completed, the school will usually hold a school building-level committee meeting (or other type of team meeting) to decide on the most appropriate interventions for your child. Specialists from gifted education, regular education, and special education should be present, as should you and the person who did the testing. Together, you can develop an effective educational program that addresses both strengths and weaknesses.
Two books you might find interesting are The Gift of Dyslexia: Why Some of the Smartest People Can't Read and How They Can Learn by Ronald D. Davis and Eldon M. Braun, and The Pretenders: Gifted People Who Have Difficulty Learning by Barbara P. Guyer.