Genetic Testing for Diagnosis of Inherited Peripheral Neuropathies AHS – M2072

Description of Procedure or Service

The inherited peripheral neuropathies are a heterogeneous group of diseases that may be inherited in an autosomal dominant, autosomal recessive or X-linked dominant manner. The inherited peripheral neuropathies can be divided into hereditary motor and sensory neuropathies (CharcotMarie-Tooth disease), hereditary neuropathy with liability to pressure palsies, hereditary sensory and autonomic neuropathies, and other miscellaneous types (e.g., hereditary brachial plexopathy, giant axonal neuropathy). In addition to clinical presentation, nerve conduction studies and family history, genetic testing can be used to diagnose specific inherited peripheral neuropathies (Cruse, 2016).

***Note: This Medical Policy is complex and technical. For questions concerning the technical language and/or specific clinical indications for its use, please consult your physician.

Policy

BCBSNC will provide coverage for genetic testing for diagnosis of inherited peripheral neuropathies when it is determined to be medically necessary because the medical criteria and guidelines shown below are met.

Benefits Application

This medical policy relates only to the services or supplies described herein. Please refer to the Member's Benefit Booklet for availability of benefits. Member's benefits may vary according to benefit design; therefore member benefit language should be reviewed before applying the terms of this medical policy.

When Genetic Testing for Diagnosis of Inherited Peripheral Neuropathies is covered

1. Genetic Counseling is considered medically necessary and recommended for genetic testing of CMT disease. 
2. Genetic Testing for CMT disease is considered medically necessary when the patient displays clinical features of CMT and a definitive diagnosis remains uncertain after history, physical examination, genetic counseling, and completion of conventional diagnostic studies (i.e. nerve conduction studies and/or electromyography). The sequence for genetic testing is as follows: 
   1. If nerve conduction studies indicate demyelinating neuropathy (velocity <38 m/s), test for the most commonly identified CMT subtype: CMT1A (PMP22 duplication). If the result is negative, multi-gene panel testing of genes GJB1 (CMTX1), MPZ (CMT1B), MFN2 (CMT2A2), LITAF (CMT1C), EGR2 (CMT1D), PMP22 sequencing (CMT1E), GARS (CMT2D), NEFL (CMT2E/1F), GDAP1 (CMT2H/2K), and SH3TC2 (CMT4C) is considered medically necessary. 
   2. If nerve conduction studies indicate axonal neuropathy (velocity >38 m/s), multigene panel testing of genes GJB1 (CMTX1), MPZ (CMT1B), LITAF (CMT1C), EGR2 (CMT1D), PMP22 sequencing (CMT1E), MFN2 (CMT2A2), GARS (CMT2D), NEFL (CMT2E/1F), GDAP1 (CMT2H/2K), and SH3TC2 (CMT4C) is considered medically necessary.
3. Genetic testing for CMT is considered medically necessary for prenatal diagnosis of known familial mutation(s) in at-risk pregnancies
4. Peripheral Nerve biopsy is considered medically necessary to diagnose CMT when clinical features are significantly suggestive of CMT and the genetic tests are negative. 
5. Genetic testing for Hereditary Neuropathy with liability to Pressure Palsies (PMP22 deletion) is considered medically necessary when the patient displays clinical features of HNPP and a definitive diagnosis remains uncertain after history, physical examination, genetic counseling, and completion of electrophysiologic studies.

When Genetic Testing for Diagnosis of Inherited Peripheral Neuropathies is not covered

Additional testing for other genes associated with CMT is considered investigational.

Genetic testing for all other inherited peripheral neuropathies is considered investigational.

Policy Guidelines

Background

Charcot-Marie-Tooth (CMT) disease, also known as Hereditary motor sensory neuropathy and peroneal muscular atrophy, is a group of progressive disorders that affect the peripheral nerves. CMT is caused by a mutation in one of several myelin genes that result in defects in myelin structure, maintenance or function. Charcot-Marie-Tooth disease is one of the most common inherited neurological disorders, affecting approximately 1 in 2,500 people in the United States.

Symptoms

The neuropathy of CMT affects both motor and sensory nerves. Symptoms usually start in childhood and have a gradual progression. The severity of symptoms varies greatly among individuals and even among family members with the disease (NINDS, 2007). Typical symptoms include the following:

• Weakness of the foot and lower leg muscles, which may result in foot drop and a highstepped gait with frequent ankle sprains, tripping or falls 
• Foot deformities, such as pes cavus and hammertoes 
• Distal calf muscle atrophy often occurs, causing the stork leg deformity or inverted champagne bottle appearance
• Weakness and muscle atrophy may occur in the hands, resulting in difficulty with carrying out fine motor skills. 
• Sensory loss is gradual and mainly involves proprioception and vibration. 
• Spinal deformities like kyphosis and scoliosis can often develop

Pain can range from mild to severe, and some people may need to rely on foot or leg braces or other orthopedic devices to maintain mobility. Although in rare cases, individuals may have respiratory muscle weakness, CMT is not considered a fatal disease and people with most forms of CMT have a normal life expectancy (NINDS, 2007).

Causes

CMT is caused by mutations in genes that produce proteins involved in the structure and function of either the peripheral nerve axon or the myelin sheath. Although different proteins are abnormal in different forms of CMT disease, all of the mutations affect the normal function of the peripheral nerves.

Pattern of Inheritance

The pattern of inheritance varies with the type of CMT disease. CMT1, most cases of CMT2, and most intermediate forms are inherited in an autosomal dominant pattern. CMT4, a few CMT2 subtypes, and some intermediate forms are inherited in an autosomal recessive pattern. CMTX is inherited in an X-linked pattern. In the X-linked recessive patterns, only males develop the disease, although females who inherit the defective gene can pass the disease onto their sons. In the X-linked dominant pattern, an affected mother can pass on the disorder to both sons and daughters, while an affected father can only pass it onto his daughters.

Some cases of CMT disease result from a new mutation and occur in people with no history of the disorder in their family. In rare cases the gene mutation causing CMT disease is a new mutation which occurs spontaneously in the individual's genetic material and has not been passed down through the family.

Types of Charcot-Marie-Tooth disease

There are many forms of CMT disease, including CMT1, CMT2, CMT3, CMT4, and CMTX.

CMT1 is a demyelinating peripheral neuropathy characterized by distal muscle weakness and atrophy, sensory loss, and slow nerve conduction velocity (typically 5-30 m/sec) (Bird, 2016). The six subtypes of CMT1 shown in Table 1 are clinically indistinguishable and are designated solely on molecular findings (Saporta et al., 2011)

CMT1A

CMT1A is an autosomal dominant disease that results from a duplication of the gene on chromosome 17 that carries the instructions for producing the peripheral myelin protein-22 (PMP-22). Overexpression of this gene causes the structure and function of the myelin sheath to be abnormal. A different neuropathy distinct from CMT1A called hereditary neuropathy with predisposition to pressure palsy (HNPP) is caused by a deletion of one of the PMP-22 genes. In this case, abnormally low levels of the PMP-22 gene result in episodic, recurrent demyelinating neuropathy (NINDS, 2007).

CMT1B

CMT1B is an autosomal dominant disease caused by mutations in the gene that carries the instructions for manufacturing the myelin protein zero (P0), which is another critical component of the myelin sheath. Most of these mutations are point mutations. As a result of abnormalities in P0, CMT1B produces symptoms similar to those found in CMT1A (NINDS, 2007).

The less common CMT1C, CMT1D, and CMT1E, which also have symptoms similar to those found in CMT1A, are caused by mutations in the LITAF, EGR2, and NEFL genes, respectively (NINDS, 2007).

CMT2

CMT2 is an axonal (non-demyelinating) peripheral neuropathy characterized by distal muscle weakness and atrophy. Nerve conduction velocities are usually within the normal range; however, occasionally they fall in the low-normal or mildly abnormal range (35-48 m/sec) (Bird, 2016). In general, individuals with CMT2 tend to be less disabled and have less sensory loss than individuals with CMT1. A threshold of 38 m/sec for median motor nerve conduction is often used clinically to distinguish CMT1 from CMT2 (Bird, 2016). It is less common than CMT1. CMT2A, the most common axonal form of CMT, is caused by mutations in Mitofusin 2, a protein associated with mitochondrial fusion. CMT2A has also been linked to mutations in the gene that codes for the kinesin family member 1B-beta protein, but this has not been replicated in other cases. Other less common forms of CMT2 are associated with various genes: CMT2B (associated with RAB7), CMT2D (GARS). CMT2E (NEFL), CMT2H (HSP27), and CMT2l (HSP22) (NINDS, 2007). 

CMT3

CMT3 or Dejerine-Sottas disease is a severe demyelinating neuropathy that begins in infancy. Infants have severe muscle atrophy, weakness, and sensory problems. This rare disorder can be caused by a specific point mutation in the P0 gene or a point mutation in the PMP-22 gene (NINDS, 2007).

CMT4

CMT4 comprises several different subtypes of autosomal recessive demyelinating motor and sensory axonal neuropathies. Each neuropathy subtype is caused by a different genetic mutation, may affect a particular ethnic population, and produces distinct physiologic or clinical characteristics. Affected individuals have the typical CMT phenotype of distal muscle weakness and atrophy associated with sensory loss and, frequently, pes cavus foot deformity. Several genes have been identified as causing CMT4, including GDAP1 (CMT4A), MTMR13 (CMT4B1), MTMR2 (CMT4B2), SH3TC2 (CMT4C), NDG1 (CMT4D), EGR2 (CMT4E), PRX (CMT4F), FDG4 (CMT4H), and FIG4 (CMT4J) (NINDS, 2007).

CMTX

CMTX is caused by a point mutation in the connexin-32 gene on the X chromosome. The connexin-32 protein is expressed in Schwann cells-cells that wrap around nerve axons, making up a single segment of the myelin sheath (NINDS, 2007). CMTX type 1 is characterized by a moderate to severe motor and sensory neuropathy in affected males and usually mild to no symptoms in carrier females. Sensorineural deafness and central nervous system symptoms also occur in some families (Bird, 2016).

Genetic Testing

Charcot-Marie-Tooth disease is usually diagnosed by an extensive medical history, family history, and physical examination. The clinical diagnosis is then confirmed by electrodiagnostic tests like electromyography and nerve conduction velocity tests, and sometimes by nerve biopsy. Genetic testing is available for some types of CMT and results are usually enough to confirm a diagnosis. Genetic testing can simplify the diagnosis of CMT by avoiding invasive procedures such as nerve biopsy. In addition, early diagnosis can facilitate early interventions such as physical therapy. However, genetic testing often will not affect the management for individual patients with CMT.

Genetic testing for CMT is complicated by the extensive underlying genetic heterogeneity (Cruse, 2017). The CMT spectrum of disorders can be inherited in an autosomal dominant, autosomal recessive, or X-linked manner. The most commonly identified CMT subtypes were CMT1A (PMP22 duplication), CMTX1 (GJB1 mutation), hereditary neuropathy with liability to pressure palsies (PMP22 deletion), CMT1B (MPZ mutation), and CMT2A (MFN2 mutation). Together, these five subtypes accounted for 92 percent of genetically defined CMT cases. All other CMT subtypes and associated mutations each accounted for <1 percent of genetically defined CMT (Cruse, 2017).

Genetic screening for relatives of a patient diagnosed with CMT is an option, but risk assessment depends on several factors, including accuracy of the diagnosis, determination of the mode of inheritance for the individual family, and results of molecular genetic testing (Cruse, 2017).

Clinical Validity and Utility

According to Cruse (2017), genetic testing to diagnose CMT can help patient avoid invasive procedures and facilitate early interventions such as physical therapy. Genetic screening in asymptomatic at-risk relatives of a patient diagnosed with CMT can be considered, but risk assessment depends on several factors, including accuracy of the diagnosis, determination of the mode of inheritance for the individual family, and results of molecular genetic testing. Genetic counseling is recommended prior to prenatal testing for pregnancies at increased risk for CMT. Prenatal testing should be done only if the pathogenic variant in the family is already known (Cruse, 2017).

Bird (1998; updated 2016) recommended testing of asymptomatic adult relatives who are at risk of developing CMT if the specific pathogenic variant has been identified in and affected relative. Genetic counseling should be performed prior to testing. Testing of at-risk asymptomatic children was not recommended. The author also stated that prenatal testing and preimplantation genetic diagnosis for some forms of CMT should be performed only if the disease-causing variant has been already identified in the family.

One potential genetic testing strategy is use of a multi-gene panel that includes genes associated with CMT (Rossor et al, 2013). Panels exist for dominantly and recessively inherited CMTs as well as demyelination and axonal forms. Larger, all-inclusive panels are also available. The genes included and the methods used in multi-gene panels vary by laboratory and over time (Bird, 1998). Another potential testing approach is to first test for pathogenic variant(s) in the single most likely gene that best fits the phenotype. If such testing does not identify the pathogenic variant, then proceed to genetic neuropathy panel testing (Rossor et al, 2015).

According to DiVincenzo et al. (2014), 95% of the positive results involved one of four genes (PMP22, GJB1, MPZ, MFN2). The authors conclude that these four genes should be screened first before proceeding with further genetic testing. Manganelli et al. (2014) essentially confirm the findings of DiVincenzo et al. except for finding a larger number of GDAP1 pathogenic variants (4%). Pareyson (2017) reviewed the current literature on CMT diagnosis summarizing: “The data justify a step-wise diagnostic algorithm based on phenotype, inheritance pattern, nerve conduction velocities, frequency of subtypes, and ethnicity. Although this approach is reasonably successful, with over 60% of patients with CMT achieving a genetic diagnosis, it is gradually being replaced by NGS techniques. Actually, a practical approach is based on the screening of few frequent genes first (PMP22, GJB1, MPZ, MFN2, GDAP1, HSPB1, HSPB8), taking into account the clinical data, and then requires the use of NGS techniques. However, multigene panel testing or whole exome sequencing (WES) can be considered first-line in many circumstances, after initial targeted testing for the PMP22 duplication in patients with demyelinating CMT. With the advent of WES, that allows the identification of new genes and the diagnosis of patients with rare and atypical conditions, the number of genes known to be associated with CMT is continuing to grow. Gene discoveries within the past two decades have challenged the simplistic classification of CMT, as for example we have reached and overcome the alphabet letters for CMT2. A novel classification based on inheritance pattern, nerve conduction values, and mutated gene has been proposed but needs further discussion and widespread agreement”

For inherited peripheral neuropathies other than CMT and HNPP, the clinical utility of genetic testing to confirm a clinical diagnosis of an inherited peripheral neuropathy is unknown. No evidence was found that use of genetic testing resulted in changes to patient monitoring and patient management and led to improvement in clinical outcomes. Genetic testing for other inherited peripheral neuropathies is, therefore, considered experimental and investigational.

Applicable Federal Regulations

This test is considered a laboratory developed test (LDT); developed, validated and performed by individual laboratories.

LDTs are regulated by the Centers for Medicare and Medicaid (CMS) as high-complexity tests under the Clinical Laboratory Improvement Amendments of 1988 (CLIA’88).

As an LDT, the U. S. Food and Drug Administration has not approved or cleared this test; however, FDA clearance or approval is not currently required for clinical use.

Guidelines and Recommendations

Practice Guidelines and Position Statements

AAN, AANEM, and AAPM&R

The Polyneuropathy Task Force that included 19 physicians with representatives from the American Academy of Neurology (AAN), the American Academy of Neuromuscular and Electrodiagnostic Medicine (AANEM), and the American Academy of Physical Medicine and Rehabilitation (AAPM&R) concluded that “genetic testing is established as useful for the accurate diagnosis and classification of hereditary polyneuropathies (Class I)” (England et al, 2009). The Task Force stated that “for patients with a cryptogenic polyneuropathy who exhibit a classic hereditary neuropathy phenotype, routine genetic screening may be useful for CMT1A duplication/deletion and Cx32 mutations in the appropriate phenotype (Class III). Further genetic testing may be considered guided by the clinical question.” The Task force recommended that “genetic testing should be conducted for the accurate diagnosis and classification of hereditary neuropathies (Level A)”. The Task force further recommended that “Genetic testing may be considered in patients with a cryptogenic polyneuropathy and classic hereditary neuropathy phenotype (Level C). There is insufficient evidence to support or refute the usefulness of routine genetic testing in cryptogenic polyneuropathy patients without a classic hereditary phenotype (Level U)” (England et al, 2009).

No guidelines or recommendations for genetic testing for inherited peripheral neuropathies other than CMT and HNPP were found from any professional association and regulatory agencies.

Billing/Coding/Physician Documentation Information

This policy may apply to the following codes. Inclusion of a code in this section does not guarantee that it will be reimbursed. For further information on reimbursement guidelines, please see Administrative Policies on the Blue Cross Blue Shield of North Carolina web site at www.bcbsnc.com. They are listed in the Category Search on the Medical Policy search page.

Scientific Background and Reference Sources

Bird, T. (1998). Charcot-Marie-Tooth hereditary neuropathy overview, updated 2016. Retrieved January, 2017

Charcot-Marie-Tooth Association. (2016). Diagnosing CMT. Retrieved January 28, 2017

Cruse, R. (2016). Hereditary primary motor sensory neuropathies, including Charcot-MarieTooth disease. Retrieved January, 2017

DiVincenzo, C., et al. (2014). The allelic spectrum of Charcot-Marie-Tooth disease in over 17,000 individuals with neuropathy. Molecular Genetics and Genomic Medicine; 2(6); 522-529

England, J, Gronseth, G.S., and Sumner, A.J. (2009). Practice parameter: the evaluation of distal symmetric polyneuropathy: the role of laboratory and genetic testing (an evidence-based review). Neurology, 72(2):185-192.

Genetic Homes Reference – NIH (2017). Charcot-Marie-Tooth disease. Accessed online on January 30, 2017 from https://ghr.nlm.nih.gov/condition/charcot-marie-tooth-disease

Manganelli F, Tozza S, Pisciotta C, Bellone E, Iodice R, Nolano M, Geroldi A, Capponi S, Mandich P, Santoro L. (2014). Charcot-Marie-Tooth disease: frequency of genetic subtypes in a Southern Italy population. J Peripher Nerv Syst. 19:292–8.

Muscular Dystrophy Association (2017). Charcot-Marie-Tooth Disease. Accessed online January 29, 2017

National Institute of Neurological Disorders and Stroke (2007) Charcot-Marie-Tooth Disease Fact Sheet. Accessed online November 15, 2016

Pareyson, D., Saveri, P., & Pisciotta, C. (2017). New developments in Charcot-Marie-Tooth neuropathy and related diseases. Curr Opin Neurol, 30(5), 471-480. doi:10.1097/wco.0000000000000474

Rossor, A.M., Polke, J.M., Houlden, H., Reilly, M.M. (2013). Clinical implications of genetic advances in Charcot-Marie-Tooth disease. Nat Rev Neurol. 9:562–71.

Rossor, A.M., Evans, M.R.B., and Reilly, M.M. (2015). A practical approach to genetic neuropathies. Pract Neurol; 15: 187-198

Saporta, A., Sottile, S., Miller, L., Feely, S., Siskind, C., & Shy, M. (2011). Charcot Marie Tooth (CMT) subtypes and genetic testing strategies. Ann Neurol., 69: 22–33. doi:10.1002/ana.22166

Policy Implementation/Update Information

1/1/2019 BCBSNC will provide coverage for genetic testing for diagnosis of inherited peripheral neuropathies when it is determined to be medically necessary because criteria and guidelines are met. Medical Director review 1/1/2019. Policy noticed 1/1/2019 for effective date 4/1/2019. (jd)