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    Agenesis of the corpus callosum with Probst bundles owing to haploinsufficiency for a gene in an 8 cM region of 6q25

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    Agenesis of the corpus callosum (ACC) is a relatively common brain abnormality resulting from developmental defects either limited to the structures leading to the proper formation of the corpus callosum or involving the embryo forebrain more generally. ACC is genetically heterogeneous with autosomal dominant, autosomal recessive, and X linked inheritance and has also been reported in subjects with aneuploidies involving several chromosomes. Among them, distal 6q deletions have been consistently reported in association with ACC, suggesting that there is a gene in the deleted region whose haploinsufficiency impairs normal corpus callosum development. We have studied a child with ACC with Probst bundles and a deletion at 6q25 of about 8 cM, from D6S1496 to D6S437. Probst bundles are the axons that should have formed the corpus callosum but, unable to cross the midline owing to absence of the massa commissuralis, they run longitudinally along the medial walls of the lateral ventricles from the frontal to the occipital lobes. Thus, their presence suggests that a gene located in the 6q deleted region is specifically involved in the formation of the massa commissuralis and that its haploinsufficiency leads to primary ACC

    Going Beyond Counting First Authors in Author Co-citation Analysis

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    The present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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