Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:3448C T) polymorphism within SCN9A (Single Nucleotide Polymorphisms database [dbSNP] rs6746030) in the affected proband, and in several unaffected family members (father and brother of proband), and reported that this polymorphism is present in 14% of ethnically matched, Caucasian control chromosomes.(8) This polymorphism, in exon 18 of SCN9A, substitutes a nonpolar tryptophan (W) for a positively charged arginine (R) at residue 1150 in the reference NaV1.
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