POSITIONAL CLONING OF THE CHEDIAK-HIGASHI-SYNDROME GENE - GENETIC-MAPPING OF THE BEIGE LOCUS ON MOUSE CHROMOSOME-13

Background: Chediak-Higashi syndrome (CHS) is a systemic disorder of h uman and mouse (beige, bg) that is characterized by aberrant intracell ular protein kinesis and lysosomal trafficking. Affected individuals e xhibit a severe primary immune deficiency that principally affects the function of granulocytes and cytolytic lymphocytes and partial oculoc utaneous albinism, platelet dysfunction, and neurodegeneration. Chedia k-Higashi syndrome is inherited as an autosomal recessive Mendelian tr ait in human and mouse and maps on proximal mouse Chromosome 13. Metho ds: To clone positionally the defective gene in CHS, we have generated a large number of backcross mice who segregate for beige, Genomic DNA from these mice was genotyped for 26 genetic markers known to map on proximal mouse Chromosome 13. Results: By segregation analysis, bg was localized to a 0.24 centiMorgan interval and was shown to cosegregate with 6 genetic markers (Nid, Estm9, D13Mit56, D13Mit162, D13Mit237, a nd D13Mit240). Two of these loci, Nid and Estm9, are genes and represe nt candidates for bg, Nidogen (Nid) encodes an extracellular matrix pr otein that is a component of basement membranes. Estm9 is a sequence t hat is transcribed ubiquitously in mouse embryos and encodes a protein of unknown function. Mutation analysis of Nid and Estm9 was undertake n in 6 bg alleles; no differences were observed between bg and coisoge nic controls by analysis of Northern blots, Southern blots, or by quan titative reverse transcription and polymerase chain reaction. Conclusi ons: These studies indicate that a genomic rearrangement affecting Nid or Estm9 does not underlie bg, The bg locus has been localized on mou se Chromosome 13 with sufficient precision to enable rapid cloning of the bg nonrecombinant interval and eventual identification of the gene for Chediak-Higashi syndrome among sequences within the interval.