Anhidrotic ectodermal dysplasia (EDA) is caused by mutations in the EDA gene encoding ectodysplasin A, a member of the TNF ligand superfamily involved in the communication between the cells. The structure of the EDA gene was investigated in three patients exhibiting clinical symptoms of EDA in an attempt to correlate the molecular findings with the phenotype of the patients. Genomic DNA was analyzed by single stranded conformation polymorphism (SSCP) followed by direct sequencing. In one of the patients, as well as in his heterozygous mother and sister, a single T insertion was evidenced in exon 3 between nucleotides 713 and 714 that changed Lys codon (AAA) into a termination codon TAA (Lys158Ter). In the other patient, A1321T transversion was demonstrated. The same mutation was found in his heterozygous mother and resulted in a change of Ileu360Asn that might generate an additional glycosylation site. In the third patient an A1285G transition was revealed. This mutation that originated de novo was localized in a region that is highly conserved in TNF ligand family and caused substitution of Ala349Thr. Localization of the mutations in the extracellular domain of ectodysplasin A suggested that the primary cause of EDA is a defect in communication between the cells responsible for the development of skin appendages. Despite a different character and localization of the mutations, no apparent correlation between phenotype and genotype of the patients was evidenced. Some differences in the patients' phenotype were observed. © 2001 Wiley-Liss, Inc.