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Molecular genetic testing is a critical procedure used to identify abnormal (expanded) alleles and to characterize specific alleles on the DMPK (DM1 protein kinase) gene, which is associated with myotonic dystrophy type 1. The DMPK 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 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 building block pattern of three amino acids: cysteine, threonine, and glycine (CTG), which typically repeats between 5 to 34 times. However, longer repeats lead to gene instability, resulting in an altered version of messenger RNA that forms clumps within the cells. When the allele contains 35 to 49 CTG repeats, it is classified as a pre-mutation, where individuals remain asymptomatic, but the risk of further expansion increases with each generation. In the mild form, the allele usually has 50 to 100 CTG repeats, while the classic form has 100 to 1000 CTG repeats, and the congenital form has more than 2000 CTG repeats. The CPT® code 81234 is used to report DMP gene analysis for detecting the presence of abnormal, expanded alleles, while CPT® code 81239 is specifically for DMPK gene analysis to determine the characteristics of these expanded alleles, including their size and any similarities or differences.
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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 may warrant this genetic testing:
The procedure for DMPK gene analysis involves several key steps to ensure accurate characterization of alleles. The following procedural steps are typically followed:
After the DMPK gene analysis is completed, the patient may receive counseling regarding the results. If expanded alleles are identified, genetic counseling is recommended to discuss the implications for the patient and their family, including the risk of transmission to future generations. Follow-up appointments may be necessary to address any health concerns related to myotonic dystrophy type 1 and to develop a management plan tailored to the individual's needs. Additionally, healthcare providers may recommend monitoring for symptoms associated with the disease, as well as potential interventions to manage any complications that arise.
| Short Descr | DMPK GENE CHARAC ALLELES | Medium Descr | DMPK GENE ANALYSIS CHARACTERIZATION OF ALLELES | Long Descr | DMPK (DM1 protein kinase) (eg, myotonic dystrophy type 1) gene analysis; characterization of alleles (eg, expanded size) | 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 |
| 90 | 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. | GA | Waiver of liability statement issued as required by payer policy, individual case |
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| 2019-01-01 | Added | Added |
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