A NEW MECHANISM IN BLUE CONE MONOCHROMATISM

Blue cone monochromatism (BCM) is a rare X-linked colour vision disord er characterized by the absence of both red and green cone sensitivity . Most mutations leading to BCM fall into two classes of alterations i n the red and green pigment gene array at Xq28. In one class the red a nd green pigment genes are inactivated by deletion in the locus contro l region. In the second class genetic rearrangements have created an i solated pigment gene that carries an inactivating point mutation. Here we describe a clinical case of BCM caused by a new mutation where exo n 4 of an isolated red pigment gene has been deleted. The finding repr esents the first intragenic deletion yet described among red and green pigment genes.