In an attempt to explore the molecular mechanisms for protein S deficiency, a patient with such a deficiency was examined at the DNA, RNA and protein levels. Nucleotide analyses revealed that the proband, the mother and the grandmother had a G → C substitution in the invariant AG dinucleotide at the splicing acceptor site of intron A/exon 2. This patient was heterozygous for this substitution and the mutant allele was inherited from the proband's mother and grandmother. Reverse transcription-polymerase chain reaction analysis demonstrated several kinds of splicing abnormalities such as exon skipping and cryptic splicing, in addition to correct splicing. Semiquantitation of mRNA for the protein S gene revealed that the amount of the proband's mRNA was reduced to 60% of normal. Thus, this mutation impaired the normal processing of mRNA for the protein S gene, resulting in the subject's severe protein S deficiency.
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