Available Assays

Only a few laboratories in the United States offer clinical molecular genetic testing for OTC deficiency. One method for mutation screening of the OTC gene is singlestrand conformation polymorphism (SSCP or DHPLC) analysis of polymerase chain reaction (PCR)-amplified exons with direct sequencing of any SSCP-positive exons.8 Approximately 230 mutations have been reported (http://www.cnmcresearch.org/OTC/). Most mutations (86%) in the OTC gene are point mutations, with G^A transitions accounting for 34% and C^T transitions accounting for 21% of the total. Approximately one third of all point mutations are at CpG dinucleotides, and 15% are at splice junctions. Although the CpG sites are recurrent mutation sites, none accounts for more than 4% of the total single-base substitutions.

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