The Arg778Leu and 2299ins-C mutations were previously reported. The Arg778Leu has been reported as the most common mutation of the WD gene in East Asian populations(3-5). However, the authors identified Arg778Leu mutation in only 5% of the studied chromosomes. Thai WD patients appear to have the lowest prevalence of Arg778Leu mutation compared to previous reports from other East Asian countries. The third mutation, 2299ins-C mutation, was a frameshift mutation, which is also one of the common mutations in various ethnic groups(2,4). All identified mutations in exon 8 accounts for 10% of the studied WD chromosomes. Therefore, analysis of Arg778Leu or exon 8 sequencing is not sufficient for routine genetic testing in the presented population. Other approaches, such as those using polymorphic dinucleotide markers or intragenic single nucleotide polymorphism markers as genetic testing may be helpful to identify pre- symptomatic siblings of the affected individuals(4,9).