AbstractRestudy of the original marker‐X family confirmed recent observations that this XLMR disorder is associated with large testes and slightly abnormal ears. However, other aspects of the phenotype were variable and a distinct facies was not evident. Significant differences in marker‐X frequency between two laboratories processing the same samples were observed. Possibly, the combination of more cells and a longer culture time in one laboratory led to a greater depletion of critical nutrients and a higher frequency of the marker‐X, but additional studies are needed. No evidence was found of a diminishing frequency of the marker‐X over a 15 year