Fluorescence in situ hybridization was used to identify the chromosomal location of the human and murine GHS-R genes (Fig. 6). To assure the accuracy of the assignment, two distinct clonal isolates from a human PAC library encoding the GHS-R were utilized for the in situ hybridization. Location of the human GHS-R gene relied on the analysis
of 80 metaphase cells for each clone, with ~ 75% of the cells exhibiting specific labeling to both sister chromatids of chromosome 3. Measurement of 10 specifically labeled chromosomes demonstrated that the positive signals correspond to region 3q26.2 at 74% distance from the centromere of the long arm of chromosome 3 (3q). Genes whose defects can result in GH deficiencies did not map to this region. However, this location is in the vicinity of the possible map position for the Brachmann-de Lange syndrome, which is characterized by prenatal and postnatal growth deficiencies, with developmental delay and dysmorphic features (21). The latter mapping data is based on chromosome duplication and translocation mutants, which always included region 3q26. However, recently a cell line with a translocation was identified, indicating that the defect could be telomeric to 3q26 (interval 3q26.31-q27.3). Given the possible proximity for the presumed Brachmann-de Lange location and the GHS-R gene, it will be of interest to determine whether Brachmann-de Lange patients have GHS-R gene deficiencies. The mouse GHS-R localized to the telomere of chromosome 3, band A3.
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