Ideogram of the X chromosome showing the position of the seven known MRX genes, two candidate MRX genes [isolated from X; autosome translocation breakpoints, indicated by an asterisk(*)], and four additional nonoverlapping intervals shown by corresponding MRX family linkage intervals. These data indicate that a minimum number of 11 (or 12 when including the candidate MRX gene DXS6673E) MRX loci exist on the X chromosome. Given the fact that only single families from a particular interval were found to have a mutation in any one of the currently identified MRX genes, the minimal number of MRX genes will at least double, that is, reach 22. The MRX numbers under and above the arrows indicate the individual MRX families with mutations in that particular MRX gene (e.g., MRX19 for RPS6KA3). The vertical bars show minimal linkage intervals of corresponding MRX families with flanking DXS markers indicated.