Adult Summary Report

Secondary Findings in Adult Subjects

Non-diagnostic, excludes newborn screening & prenatal testing/screening

• Status (Adult): Passed (Consensus scoring is Complete)
• Curation Status (Adult): Released - Under Revision 2.2.2
• Status (Pediatric): Incomplete (Consensus scoring is Incomplete)
• GENE/GENE PANEL: PMP22
• Condition: Hereditary Neuropathy with Liability to Pressure Palsies
• Mode(s) of Inheritance: Autosomal Dominant

Actionability Assertion

• PMP22 ⇔ 0008087 (neuropathy, hereditary, with liability to pressure palsies; hnpp): Limited Actionability

Actionability Rationale

All experts agreed with the assertion computed according to the rubric.

Final Consensus Scores

Gene Condition Pairs: PMP22 ⇔ 0008087 (OMIM:162500)

Outcome / Intervention Pair	Severity	Likelihood	Effectiveness	Nature of the Intervention	Total Score
Neuropathy / Avoidance of triggers	1	3C	0C	3	7CC

1. What is the nature of the threat to health for an individual carrying a deleterious allele?

Prevalence of the Genetic Condition

The prevalence of hereditary neuropathy with liability to pressure palsies (HNPP) is not well known, though it has been estimated between 1/50,000 and 1/14,000. The actual prevalence may be higher because of under diagnosis. A study of the Finnish population found that prevalence may be as high as 1/6,250. [1, 2, 3]

Clinical Features

HNPP is characterized by episodic focal motor and sensory peripheral neuropathies in the hands and feet. These attacks are typically painless. The nerve palsies often recur over a period of many years, but some individuals have a single episode and others with a pathogenic variant remain asymptomatic. In many cases these symptoms are triggered by mechanical stresses to the nerve, such as compression, repetitive movement and/or stretching of the affected limbs. Common clinical manifestations include carpal tunnel syndrome and peroneal palsy with foot drop. In 50% of cases, recovery from the acute neuropathy is complete within a few days to months. Incomplete recovery is common, though the resulting disability rarely severe. Chronic motor deficits after nerve palsies are noted in 10-15%. In rare cases, strenuous activities can lead to severe and prolonged limb paralysis.
Atypical presentations of HNPP are common and can include: recurrent positional short-term sensory symptoms, progressive mononeuropathy, Charcot-Marie-Tooth like polyneuropathy, chronic sensory polyneuropathy, and chronic inflammatory demyelinating polyneuropathy-like disorder. [1, 2, 3]

Natural History

Most individuals with HNPP typically experience their first episode in the second or third decade at a mean age of 37 years, but with a large range from birth through the eighth decade. The most common presenting symptom is acute onset of a focal neuropathy of a single nerve (mononeuropathy). Males and females are equally affected. Occasional episodes have been reported during pregnancy, likely related to physiological changes. Older patients often develop a symmetric sensory motor polyneuropathy. HNPP is not life threatening, and patients have a normal life expectancy. [1, 2, 3]

2. How effective are interventions for preventing harm?

Patient Management

To establish the extent of disease following diagnosis the following evaluations are recommended:
• History of focal nerve symptoms
• Family history
• Neurologic examination
• Electromyography/nerve conduction velocity
• Clinical genetics consultation. (Tier 4) [1]

Protective pads at the elbows or knees may prevent pressure and trauma to local nerves. (Tier 4) [1, 2]

Surveillance

No surveillance recommendations have been provided for the Adult context.

Circumstances to Avoid

Patients are advised to avoid prolonged sitting with legs crossed, prolonged leaning on the elbows, occupations requiring repetitive movements of the wrist, and rapid weight loss as these have been reported in case reports as being associated with the onset of HNPP symptoms. (Tier 3) [1, 3]

Vincristine, used in chemotherapy, has been reported to exacerbate HNPP. A single case report related to this exposure was identified. No studies were identified reporting the rate of developing HNPP symptoms following vincristine exposure (Tier 3) [1, 3]

An overview of case reports addressing Charcot Marie Tooth (CMT) and toxic medication effects identified 22 reports (30 patients) addressing vincristine toxicity; however it is unclear whether this evidence may apply to HNPP. 18 of 30 patients developed marked sensory symptoms or new onset weakness, with some developing dysarthria and dysphagia. Nearly all reports describe eventual improvement, but frequently not to baseline levels. These cases occurred in both adults (15) and children (15). Most individuals having a reaction were previously unsuspected or undiagnosed with CMT (26 of 30) and were only recognized following administration of vincristine; however, 10 cases, in retrospect, had overt clinical signs or a close relative with known CMT. (Tier 5) [4]

3. What is the chance that this threat will materialize?

Mode of Inheritance

Autosomal Dominant

Prevalence of Genetic Variants

The prevalence of pathogenic variants in PMP22 associated with HNPP was unavailable. However, PMP22 accounts for an estimated 100% of HNPP cases and thus the prevalence of pathogenic variants in PMP22 is expected to be similar to the prevalence of HNPP, or between 1/50,000 and 1/20,000. (Tier 4) [1, 2, 3]

Penetrance

Studies screening relatives of index patients have identified that 6-23% of family members may be asymptomatic. These rates are not reported within the context of the exposure to potential triggers. (Tier 3) [3]

Relative Risk

Information regarding relative risk was unavailable.

Expressivity

Large intrafamilial clinical variability has been noted. (Tier 4) [1, 3]

4. What is the Nature of the Intervention?

Nature of Intervention

The interventions identified in this report include wearing protective pads and avoidance of potential triggers including vincristine.

5. Would the underlying risk or condition escape detection prior to harm in the setting of recommended care?

Chance to Escape Clinical Detection

Individuals with HNPP are typically identified after their first episode and diagnosed via genetic testing and/or electrophysiological studies. Thus, patients are likely to escape detection prior to their first episode. Given pain is often a presenting symptom, individuals with HNPP are often clinically misdiagnosed with fibromyalgia upon presentation. (Tier 4) [1, 3]

Date of Search: 05.13.2014 (updated 04.26.2018)

Reference List

1. TD Bird. Hereditary Neuropathy with Liability to Pressure Palsies. 1998 Sep 28 [Updated 2014 Sep 25]. In: RA Pagon, MP Adam, HH Ardinger, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from: http://www.ncbi.nlm.nih.gov/books/NBK1392

2. Hereditary neuropathy with liability to pressure palsies. Orphanet encyclopedia, http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=en&Expert=640

3. van Paassen BW, van der Kooi AJ, van Spaendonck-Zwarts KY, Verhamme C, Baas F, de Visser M. PMP22 related neuropathies: Charcot-Marie-Tooth disease type 1A and Hereditary Neuropathy with liability to Pressure Palsies. Orphanet J Rare Dis. (2014) 9:38.

4. Weimer LH, Podwall D. Medication-induced exacerbation of neuropathy in Charcot Marie Tooth disease. J Neurol Sci. (2006) 242(1-2):47-54.