Genomic DNA of 41 unrelated patients affected with the classical severe form of Menkes disease was investigated for point mutations in the A TP7A gene (previously designated as the ''MNK'' gene). Using SSCP analysis and direct sequencing of the exons amplified by PCR, we identified 41 different mutations, including 19 insertions/deletions, 10 nonsense mutations, 4 missense mutations, and 8 splice-site alterations. Approximately 90% of the mutations were predicted to result in the truncation of the protein (ATP7A). In 20 patients the mutations were within exons 7-10, and half of these mutations affected exon 8. Furthermore, five alterations were observed within the 6-bp sequence at the splice-donor site of intron 8, which would be predicted to affect the efficiency of splicing of exon 8. Although a specific function has not been attributed to the protein region encoded by this exon, this region may be important in serving as a ''stalk'' joining the metal-binding domains and the ATPase core. The present findings not only help us in understanding the underlying genetic defect but are invaluable data especially for carrier detection and prenatal diagnosis of this lethal disorder.