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Test Code Myoto Dyst Myotonic Dystrophy DNA

Clinical System Name

Myotonic dystrophy DNA


Myotonic Dystrophy Type 1




Myotonic dystrophy type 1 (DM1) is a multisystem disorder that affects skeletal and smooth muscle as well as the eye, heart, endocrine system, and central nervous system. The clinical findings, which span a continuum from mild to severe, have been categorized into three somewhat overlapping phenotypes: mild, classic, and congenital.  DM1 is caused by expansion of a CTG trinucleotide repeat in the non-coding region of DMPK. The diagnosis of DM1 is suspected in individuals with characteristic muscle weakness and is confirmed by molecular genetic testing of DMPK. CTG repeat length exceeding 34 repeats is abnormal. Molecular genetic testing detects mutations in nearly 100% of affected individuals.

Sample Requirements

Specimen: Whole Blood

Container(s): Lavender Top/EDTA, Yellow Top/ACD

Preferred Vol: 5.0 mL

Minimum Vol: 3.0 mL


Specimen: DNA

Container(s): Sterile Plastic Tube

Preferred Vol: 15 micrograms, concentration: at least 1 microgram/microliter

Minimum Vol:

Processing Instructions

Reject due to:

Spin: N

Aliquot: N

Temp: RT

Storage location: Affix large Cerner labels to tubes and place in room temperature Send Outs rack.


Off-site collection: Send whole blood refrigerated.


Specimen Type Temperature Time
Whole Blood Room temp 3 d
Whole Blood Refrigerated 7 d
Whole Blood Frozen N
Extracted DNA Room temp 3-4 d
Extracted DNA Refrigerated 1 y
Extracted DNA Frozen Indefinitely



No 21 days


Performing Laboratory

Baylor College of Medicine

Baylor Genetics Laboratories

2450 Holcombe - Grand Blvd Dock

Houston, TX 77021-2024


Phone: (800) 411-4363



Department: Send Outs

Phone Number: (206) 987-2563

Reference Range

DMPK alleles with >49 repeats are abnormal; alleles with <35 repeats are normal. individuals with 35-49 repeats (premutation alleles) do not have symptoms but their children are at increased risk of inheriting larger repeats and having symptoms.


Method: PCR-amplification, Southern Blot with densitometry

Analytical Volume:


CPT Codes

81401 (x1)

Clinical Utility

Indications for testing include:
- Confirm a clinical diagnosis of myotonic dystrophy
- Evaluate suspected myotonic dystrophy
- Presymptomatic testing of adults at-risk for myotonic dystrophy (in conjunction with genetic counseling)
- Prenatal diagnosis of an at-risk pregnancy
- Differential diagnosis of neonates with unexplained hypotonia and/or respiratory distress

Send Out Instructions

Reference Test Name: Myotonic Dystrophy Type 1 Repeat Expansion Analysis
Reference Test Number: 6041
Instructions: Ship at room temperature, avoid freezing sample. Send overnight via FedEx.