Figure 1.
Targeted long-read sequencing simultaneously detects repeat expansion and methylation status
Expansion and methylation of a GGC repeat in the 5′ UTR of XYLT1 is a common cause of Baratela-Scott syndrome.
(A) Southern blot of family 04 reported by LaCroix and colleagues26 demonstrates that the proband (04-01) carries an expansion (1) of a region defined by two KpnI restriction enzyme sites containing a GGC repeat, the mother (04-02) carries one premutation (2) and one wild-type allele (3), and the father (04-03) carries two wild-type alleles (4). Both panels are from the same Southern blot on day 6 of exposure.
(B) T-LRS of the trio revealed that the length of fragments from single reads spanning both KpnI cut sites used in (A) was consistent with the results from the Southern blot. Colored dots in (B) correspond to methylated (red) and non-methylated (blue) reads shown in (C); gray represents reads where methylation status was not determined.
(C) Expansion of the GGC repeat in the proband results in methylation of the 5′ UTR and exon 1. Two reads in the mother are methylated (red), one of which spans the region between the KpnI cut sites and whose length is consistent with a premutation allele as shown in (B). The second methylated read terminates within the repeat and the length cannot be assayed.