CPT® Code 81234

Official Description

DMPK (DM1 protein kinase) (eg, myotonic dystrophy type 1) gene analysis; evaluation to detect abnormal (expanded) alleles

Common Language Description

Molecular genetic testing is a critical procedure used to identify abnormal (expanded) alleles within the DMPK (DM1 protein kinase) gene, which is associated with myotonic dystrophy type 1. This gene is located on the long (q) arm of chromosome 19 at position 13.32 (19q13.32) and plays a vital role in coding a protein that facilitates communication and impulse transmission between cells in various tissues, including the heart, central nervous system, and skeletal muscles. Myotonic dystrophy type 1 manifests through a range of symptoms, including fatigue, muscle pain, difficulty swallowing, cataracts, cardiac conduction defects, respiratory complications, and male balding and infertility. The disease can be classified into three forms: mild, classic, and congenital. The mild form typically allows individuals to maintain a normal lifespan, with muscle weakness primarily affecting the lower legs, hands, face, and neck, usually beginning around the ages of 20 to 30. The classic form is associated with a shortened lifespan and presents with more severe muscle weakness and wasting, prolonged muscle tensing (myotonia), cataracts, and abnormal cardiac function. The congenital form is the most severe, characterized by generalized hypotonia and muscle weakness at birth, respiratory distress, and a high risk of early death. The DMPK gene features a unique DNA allele with a trinucleotide pattern of cysteine, threonine, and glycine (CTG), which typically repeats between 5 to 34 times. However, longer repeats lead to gene instability, resulting in an altered messenger RNA that forms clumps within cells. Alleles with 35 to 49 CTG repeats are classified as pre-mutations, where individuals remain asymptomatic, but the risk of further expansion increases with each generation. In the mild form, the allele usually contains 50 to 100 CTG repeats, while the classic form has 100 to 1000 repeats, and the congenital form exceeds 2000 repeats. The CPT® Code 81234 specifically reports the DMPK gene analysis aimed at detecting the presence of these abnormal, expanded alleles.

1. Indications

The DMPK gene analysis is indicated for the evaluation of individuals suspected of having myotonic dystrophy type 1 based on clinical symptoms or family history. The following conditions warrant this genetic testing:

Myotonic Dystrophy Type 1 Symptoms Symptoms such as fatigue, muscle pain, difficulty swallowing, cataracts, cardiac conduction defects, respiratory complications, and male balding and infertility may indicate the need for testing.
Family History A family history of myotonic dystrophy type 1 or related symptoms may prompt genetic testing to assess the risk of the disease in relatives.
Classification of Disease Individuals presenting with signs of mild, classic, or congenital forms of myotonic dystrophy type 1 may require testing to confirm the diagnosis and understand the genetic basis of their condition.

2. Procedure

The procedure for DMPK gene analysis involves several key steps to ensure accurate detection of abnormal alleles:

Step 1: Sample Collection A biological sample, typically blood or saliva, is collected from the patient. This sample serves as the source of DNA for analysis.
Step 2: DNA Extraction The DNA is extracted from the collected sample using standardized laboratory techniques to isolate the genetic material necessary for testing.
Step 3: PCR Amplification Polymerase chain reaction (PCR) is employed to amplify the specific region of the DMPK gene that contains the CTG repeat sequence. This step is crucial for obtaining sufficient quantities of DNA for analysis.
Step 4: Analysis of CTG Repeats The amplified DNA is analyzed to determine the number of CTG repeats present in the DMPK gene. This analysis helps identify whether the allele is normal, a pre-mutation, or expanded.
Step 5: Interpretation of Results The results are interpreted by a qualified geneticist or laboratory professional, who assesses the presence of abnormal alleles and provides a report detailing the findings.

3. Post-Procedure

After the DMPK gene analysis, patients may receive counseling regarding the results, especially if abnormal alleles are detected. Genetic counseling is essential to discuss the implications of the findings, potential risks for family members, and options for management or further testing. Patients may also be advised on monitoring for symptoms associated with myotonic dystrophy type 1 and the importance of regular follow-up with healthcare providers to manage any emerging complications related to the condition.

Short Descr	DMPK GENE DETC ABNOR ALLELE
Medium Descr	DMPK GENE ANALYSIS EVAL DETECT ABNORMAL ALLELES
Long Descr	DMPK (DM1 protein kinase) (eg, myotonic dystrophy type 1) gene analysis; evaluation to detect abnormal (expanded) alleles
Status Code	Statutory Exclusion (from MPFS, may be paid under other methodologies)
Global Days	XXX - Global Concept Does Not Apply
PC/TC Indicator (26, TC)	9 - Not Applicable
Multiple Procedures (51)	9 - Concept does not apply.
Bilateral Surgery (50)	9 - Concept does not apply.
Physician Supervisions	09 - Concept does not apply.
Assistant Surgeon (80, 82)	9 - Concept does not apply.
Co-Surgeons (62)	9 - Concept does not apply.
Team Surgery (66)	9 - Concept does not apply.
Diagnostic Imaging Family	99 - Concept Does Not Apply
CLIA Waived (QW)	No
APC Status Indicator	Service Paid under Fee Schedule or Payment System other than OPPS
Type of Service (TOS)	5 - Diagnostic Laboratory
Berenson-Eggers TOS (BETOS)	none
MUE	1

Reference (outside) laboratory: when laboratory procedures are performed by a party other than the treating or reporting physician or other qualified health care professional, the procedure may be identified by adding modifier 90 to the usual procedure number.

Repeat clinical diagnostic laboratory test: in the course of treatment of the patient, it may be necessary to repeat the same laboratory test on the same day to obtain subsequent (multiple) test results. under these circumstances, the laboratory test performed can be identified by its usual procedure number and the addition of modifier 91. note: this modifier may not be used when tests are rerun to confirm initial results; due to testing problems with specimens or equipment; or for any other reason when a normal, one-time, reportable result is all that is required. this modifier may not be used when other code(s) describe a series of test results (eg, glucose tolerance tests, evocative/suppression testing). this modifier may only be used for laboratory test(s) performed more than once on the same day on the same patient.