Somatic revertant mosaicism of the SAMD9L mutations. (A-B) Quantification of the frequency of the (A) SAMD9L c.2956C>T in family 1 and (B) SAMD9L c.2672T>C in family 2 relative to the wild-type allele in peripheral blood–derived DNA, as assessed by mutation-specific dPCR assay. (C) Additional quantification of the frequency of the SAMD9L c.2956C>T in DNA from a Guthrie card dried blood spot and a buccal swab from F1:III-2. For each sample, values represent the mean of at least 2 chips. Error bars denote 95% confidence levels. (D) Allele frequency of phased heterozygous variants on chromosome 7 of F1:III-2, as calculated from the allelic read-depth from WES data. The variants are color-coded on the basis of the parental origin, as indicated. The gray vertical lines indicate the centromere of chromosome 7, and the dashed line indicates the position of the SAMD9L c.2956C>T mutation. (E) Log R ratio of intensity signal and B-allele frequency for SNP on chromosome 7 of F2:II-1, as determined by SNP array. The dashed vertical line indicates the position of the SAMD9L c.2972T>C mutation. (F) Sanger traces from members of family 2, as indicated, for the SAMD9L c.2302A>T nonsense mutation identified in F2:I-2 (arrow). (G) Schematic representation of the genotype of PCR-derived SAMD9L clones spanning the SAMD9L c.2302A>T and c.2972T>C mutations. Open circles represent wild-type (wt) nucleotide sequence, whereas filled circles represent mutated (mut) nucleotide sequence.