In 1987 a new concept in the X-linked muscular dystrophies was born with the identification of dystrophin, a cytoskeletal protein responsible for several muscular diseases previously grouped as Duchenne's or Becker's muscular dystrophies (DMD and BMD, respectively). Under the new concept these entities are referred to as dystrophinopathies. The discovery of dystrophin was made possible when polymerase chain reaction and reverse genetics opened the door to DNA examination. The DMD/BMD gene was located and sequenced and the protein product, dystrophin, was fully identified. The genetic study of dystrophinopathies was extended in the 1990's to include DNA analysis aimed at 1) discovering points of deletion or mutation that give rise to Xp21 myopathies, as dystrophinopathies are also known; 2) identifying the rules of protein translation (interruption or reading "signals" of the protein's genetic code), and 3) identifying atypical clinical phenotypes that can be diagnosed on a molecular level using anti-dystrophin antibodies or DNA probes.