Blue cone monochromacy is a rare X-linked disorder of color vision characterized by the absence of both red and green cone sensitivities. In 12 of 12 families carrying this trait, alterations are observed in the red and green visual pigment gene cluster. The alterations fall into two classes. One class arose from the wild type by a two-step pathway consisting of unequal homologous recombination and point mutation. The second class arose by nonhomologous deletion of genomic DNA adjacent to the red and green pigment gene cluster. These deletions define a 579-base pair region that is located 4 kilobases upstream of the red pigment gene and 43 kilobases upstream of the nearest green pigment gene; this 579-base pair region is essential for the activity of both pigment genes.
Virtual reality surgical simulator training mildly shortens the learning curve for the first 50 phacoemulsification cases. The less adept residents appear to benefit most.
Two adolescent boys with Kearns-Sayre syndrome (progressive external ophthalmoplegia, heart block, elevated CSF protein, and ragged-red muscle fibers) developed lethargy, increasing somnolence, polydipsia, polyphagia, and polyuria after a brief course of steroid therapy. Both had hyperglycemia and acidosis. Nonketotic, lactic acidosis was present in one and ketosis in the other. Severe respiratory failure developed, and both patients died. Postmortem revealed fatty infiltration of the pancreas in addition to a diffuse spongiform encephalopathy.
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