Long-Read Sequencing

Massive Tandem Repeat Panel (dmTGS)

Pioneers in Reaching Repeat Expansion Disorders

LRS Opens New Frontiers in Repeat Expansion Disorders

Advances in LRS have revolutionized the discovery of repeat expansion disorders. Nearly half of these disorders were discovered in the last decade, overcoming the limitations of older methods.

Apart from NGS (short-read lengths and GC bias) or limited routine PCR assays, LRS offers a clear advantage. It generates reads that span entire repeat regions. This allows for precise, simultaneous detection of repeat counts, unit sizes, and sequence interruptions for a group of genes in a single test.

Timeline of repeat expansion discovery in human disorders

Figure from reference¹

dmTGS: A Comprehensive Tandem Repeat Panel

Diagnosing tandem repeat disorders is clinically challenging due to high phenotypic variability, often requiring molecular testing to aid in diagnosis. The dmTGS test provides a precise molecular solution using SMRT sequencing technology.

Covers 68 disorders associated with 63 genes in one assay
Replaces multiple single-gene tests, significantly shortening the diagnostic time
Ideal for undiagnosed cases of ataxia, neuromuscular and neurodevelopmental disorders

Technology Comparison: dmTGS vs. PCR and NGS

Items

PCR methods

Southern Blot

NGS

dmTGS

Repeat count accuracy

Low

Limited to count

Limited to length <150bp

High

Gene per assay

1-10

10-30

(Most up to date)

Large repeat units (VNTR)

✔

Interruptive motifs

✔

Extrene GC

✔

Features

High Resolution

Precisely distinguishes pathogenic from non-pathogenic repeat counts (down to single-repeat accuracy). This reduces uncertainty in borderline cases.

High Sensitivity to Mosaicism

Detects low-level mosaicism (e.g. 1% for FMR1 CGG premutations and 5% for full mutations²)

Accurate Interruptive Motif Detection

Identifies interruptions within repetitive sequences that impact genetic stability and disease severity.

Characterization of Polymorphic Sequences

Unlike Nanopore sequencing (which has higher error rates) or PCR (limited by size), dmTGS with SMRT sequencing resolves complex VNTRs spanning dozens of kilobases.

Proven Clinical Performance

Superior resolution compared to RP-PCR, AL-PCR, and Sanger sequencing²
Accurately characterizes complex 99-mer VNTRs (e.g., PLIN4)²
Corrects false-negatives from NGS and PCR by identifying 3′-end interrupting motifs that block PCR primer²

Send-out Testing

When considering our send-out sequencing services:

Consultation: Contact our team for the most current test specifications.
Sample Preparation: Check sample types and shipment requirements to ensure high-quality results. Please check your local export regulations and logistics partners.
Submission: Contact Xcelom when placing an order. Include the completed Test Request and Consent Form, along with any required documents.

Sample Requirements

Peripheral Blood: 2 mL in EDTA tube

Long-fragment gDNA

Transport Conditions

2-8℃, arrive within 72 hours
Dry ice transportation, arrive within 5 calendar days

Testing Scope

Detection of abnormal repeat numbers across 63 genes associated with 68 diseases

Turnaround Time (TAT)

29 working days

End-to-End Technology Transfer

Berry Genomics and Xcelom provide dedicated turnkey solution to bring this capability into your laboratory. We offer end-to-end support, including:

Lab Setup: Consultation on workflow, equipment, and customized kits.
Training: Comprehensive wet-lab training for your staff.
Bioinformatics Support: Our tailored software solutions streamline variant annotation and interpretation, automatically integrating public databases to assist with ACMG analysis.

Resources

dmTGS Brochure

References:

1. Depienne C, Mandel JL. 30 years of repeat expansion disorders: What have we learned and what are the remaining challenges?. Am J Hum Genet. 2021;108(5):764-785.

2. Yang K, Liu Y, Zhang J, et al. dmTGS: Precise Targeted Enrichment Long-Read Sequencing Panel for Tandem Repeat Detection. Clin Chem. 2025;71(2):319-331.