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Myotonic Dystrophy
Short Description : Myotonic dystrophy genetic testing

Test performed by: LabPLUS - Dept. Diagnostic Genetics - Molecular Genetics

Referral Requirements

Important Note:

Diagnostic testing requires referral through Neurology, Paediatrics or Genetic Services.

Predictive testing only through Genetic Services.


Genetic Health Service NZ can be contacted on 0800 476 123.

Neurology can be contacted on (09) 307 4949 ext. 25662.

General Paediatrics can be contacted on (09) 307 4949 ext. 22559.

Specimen Collection
EDTA4 mL Paediatric EDTA Blood (Preferred)


For paediatric samples a minimum of 0.5ml blood EDTA can be processed. (Microcollect)

Transport all bloods at room temperature within 24-48 hours. If necessary specimens can be refrigerated overnight for transport at room temperature the following day.

For testing of other sample types please contact the laboratory prior to sending.

EDTA8 mL Adult EDTA Blood
Turnaround Time: Within 6 weeks
Contact Information

Contact Molecular Genetics via:

Lablink                                                     ext 22000

Mark Greenslade (Technical Head)   ext 22010

Pippa Grainger (Section leader)              ext 22014

Email: DGen@adhb.govt.nz

Background Information

Myotonic dystrophy type 1 (DM1) is suspected in adults with the following:  Muscle weakness, especially of the distal leg, hand, neck, and face Myotonia (sustained muscle contraction), which often manifests as the inability to quickly release a hand grip (grip myotonia) and which can be demonstrated by tapping a muscle (such as the thenar muscles) with a reflex hammer (percussion myotonia). Posterior subcapsular cataracts detectable as red and green iridescent opacities on slit lamp examination. DM1 is suspected in neonates with some combination of hypotonia, facial muscle weakness, generalized weakness, positional malformations including club foot, and respiratory insufficiency.

DM1 is caused by expansion of a CTG trinucleotide repeat in the gene DMPK . The diagnosis of DM1 is suspected in individuals with characteristic muscle weakness and is confirmed by molecular genetic testing of DMPK. Molecular genetic testing detects mutations in nearly 100% of affected individuals.

For more information about the Molecular Genetics service:

Molecular Genetics information page

Last updated at 15:49:04 22/03/2021