Pediatric Summary Report

Secondary Findings in Pediatric Subjects

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

• Status (Pediatric): Passed (Consensus scoring is Complete)
• Curation Status (Pediatric): Released 2.0.0
• Status (Adult): Passed (Consensus scoring is Complete)
• GENE/GENE PANEL: PMP22
• Condition: Hereditary Neuropathy with Liability to Pressure Palsies
• Mode(s) of Inheritance: Autosomal Dominant

Actionability Assertion

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

Actionability Rationale

The score from the rubric suggested moderate actionability but all scorers asserted limited actionability. This was driven by significant concerns over the level of evidence for the likelihood of events during the pediatric period and for the effectiveness of the intervention during that time.

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 and neurotoxic drugs	1	3D	1D	3	8DD

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 1/6,250 in different populations. The actual prevalence may be higher because of under diagnosis. [1, 2, 3, 4]

Clinical Features

HNPP is characterized by episodic focal motor and sensory peripheral neuropathies. Individuals with HNPP present with variously located recurrent peripheral nerve palsies, or sensory loss. The most common initial manifestations include the acute onset of a focal sensory and motor neuropathy in a single nerve (mononeuropathy). These attacks are typically painless. 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, hand numbness and weakness, arm weakness, sensory loss, and peroneal palsy with foot drop. Neuropathic pain is increasingly recognized as a common manifestation. Absent deep tendon reflexes and pes cavus foot deformity are seen in some individuals.
Atypical presentations of HNPP are common and can include recurrent positional short-term sensory symptoms, progressive sensorimotor mononeuropathy, Charcot-Marie-Tooth like polyneuropathy, chronic sensory polyneuropathy, and chronic inflammatory demyelinating polyneuropathy-like disorder. [1, 2, 3, 4, 5]

Natural History

Most individuals with HNPP typically experience their first episode in the second or third decade at a mean age of 37 years (age range 2-70 years), but with a large range from birth through the eighth decade. While the nerve palsies often recur over a period of many years, some individuals have a single episode, and some remain asymptomatic. 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 is 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. Nerve palsies and electrophysiologic abnormalities are more frequent in men than women. 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, 4, 5]

2. How effective are interventions for preventing harm?

Patient Management

To establish the extent of disease following diagnosis the following evaluations are recommended:
•Neurologic examination
•Orthopedics, physical medicine and rehab, PT, OT evaluation
•Clinical genetics consultation. (Tier 4) [4]

Electrophysiological examination (electromyography/nerve conduction velocity) is of great importance for diagnosis of HNPP. Nerve conduction studies reveal a characteristic pattern, even in clinically non-affected nerves or in asymptomatic at-risk individuals. (Tier 4) [1, 3, 4, 5]

Consultation should be provided to the individual about physical activities that may trigger the sensory/motor deficits. (Tier 4) [1, 3]

Protective pads at the elbows or knees may prevent pressure and trauma to local nerves. Management during a pressure palsy may include transient bracing and special shoes. If a pressure palsy is not transient but residual, the bracing may need to be permanent. (Tier 4) [1, 3, 4]

Particular care must be taken in positioning during surgery (particularly knee surgery) to avoid nerve compression. (Tier 3) [4]

Surveillance

The following surveillance is recommended for individuals with HNPP annually:
•Screening neurologic exam focused on muscle atrophy, strength, and sensory loss
•Evaluation for neuropathic pain
•Physical therapy evaluation, occupational therapy evaluation, including evaluation of activities of daily living
•Foot examination for pressure sores or poorly fitting footwear. (Tier 4) [4]

Circumstances to Avoid

Activities that are risk factors for pressure palsies include prolonged sitting with legs crossed, prolonged leaning on the elbows, occupations requiring repetitive movements of the wrist, rapid weight loss, and wearing a heavy backpack on the shoulders. (Tier 3) [3, 4]

In a study of 51 individuals with molecularly confirmed HNPP (mean age at diagnosis 20 years; range 10-29 years) 61% had a precipitating factor. Contributing factors included > 1 hour of nerve compression in 54% and minor compression or slight trauma (brief limb hyperextension, crossed leg position, minor fall) in 46%. (Tier 5) [6]

In a cohort of 12 symptomatic children (age range 3-16 years) with molecularly confirmed HNPP, injury or trigger for demyelination was clearly identified in 42%. Most of the time the trigger was related to heavy pressure (e.g., carried a heavy backpack) or significant weight loss. (Tier 5) [7]

Caution should be exercised, and patients should be informed about potentially neurotoxic drugs that may worsen their symptoms. A review concluded that use of vincristine (30 included papers), and possibly paclitaxel (6 included papers), can occasionally induce an atypical, and more severe, course of drug-related peripheral neurotoxicity in individuals with CMT (also caused by variants in PMP22). However, it is unclear whether this evidence may apply to HNPP. (Tier 2) [8]

Vincristine, used in chemotherapy, has been reported to exacerbate HNPP. A single case report related to this exposure was identified. A 37-year-old male with HNPP developed tetraparesis and severe weakness of the upper and lower extremities following chemotherapy treatment that included vincristine. (Tier 3) [2, 3, 4]

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

Mode of Inheritance

Autosomal Dominant [4]

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. (Tier 4) [4]

A 1.5 megabase recurrent deletion or a novel deletion involving PMP22 is found in 80% of individuals and a PMP22 sequence variant in 20%. Approximately 20% of individuals with HNPP have the disorder as the result of a de novo variant. (Tier 3) [3, 4]

Penetrance

Penetrance is 100% but expressivity is highly variable even within the same family. (Tier 4) [4]

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, 4]

Nerve conduction studies reveal diffuse abnormalities in all individuals with pathogenic variants, symptomatic or not, aged more than 15 years. (Tier 3) [3, 5]

In one cross-sectional study of 43 individuals with a self-reported molecular diagnosis of HNPP (mean age 47 years), 74% of individuals had persistent pain. Of these, three quarters developed neuropathic pain and almost 90% were likely to have central sensitization (i.e., development and maintenance of chronic pain). (Tier 3) [4]

Mild to moderate pes cavus foot deformity is seen in 4 to 47% of individuals. (Tier 4) [3, 4]

One study reported 99 individuals with a molecular and clinical diagnosis of HNPP that were seen in a single neurogenetic department. Age at exam ranged from 5 to 73 years.
•71% presented with at least one peripheral nerve palsy. Of these individuals, residual motor deficits at least 3 months after the last acute palsy were observed in 15%.
•15% presented with uncommon clinical features of HNPP including recurrent short-term positional sensory symptoms, chronic sensory polyneuropathy, chronic paresthesias, pes cavus and areflexia.
•14% were asymptomatic (age range 5 to 67 years) (Tier 5) [9]

Another study reported 73 individuals (mean age 43 years; range 17 to 84 years) with a molecular and clinical diagnosis of HNPP that were followed at a single center over a 20-year period.
•44% presented with recurrent multiple mononeuropathies, starting acutely without pain, followed by complete recovery
•16% presented with a history of chronic ulnar neuropathy at the elbow
•13% presented with symptoms of carpal tunnel syndrome
•9% presented with a history of lower limb paresthesia
•9% presented with pes cavus and mild weakness in the intrinsic feet muscles
•3% had a Guillain-Barre-like presentation
•12% were asymptomatic for neuropathic symptoms (Tier 5) [10]

Relative Risk

Information regarding relative risk was unavailable.

Expressivity

There is large clinical variability between individuals with HNPP. At the mild end of the spectrum, individuals can be clinically asymptomatic. At the severe end of the spectrum individuals have residual symptoms after nerve palsies, which can mimic a CMT phenotype. Intrafamilial variability is considerable. (Tier 3) [3, 4]

Pathogenic single nucleotide variants in PMP22 may result in HNPP or CMT1A. (Tier 4) [2]

4. What is the Nature of the Intervention?

Nature of Intervention

Potential interventions include examinations (physical exam, nerve conduction studies) and avoidance of certain triggers and medications. Nerve conduction studies are generally well tolerated and pose little risk to patients of serious adverse events. Mild procedural pain and discomfort are very common (≥1 in 10 persons). The discomfort, or mild pain experienced by some patients, following the application of electrical stimulation during nerve conduction studies is transient and self-limiting and will not initiate or aggravate pre-existing symptoms beyond the duration of the actual investigation. Vincristine is the most used vinca alkaloid in pediatric patients. Treatment substitution with the pharmacologically similar, but possibly less neurotoxic, vindesine has been reported to be successful in one individual with CMT1A. [11, 12]

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

Chance to Escape Clinical Detection

HNPP is probably underdiagnosed because it typically has episodic and transient clinical manifestations. (Tier 3) [2]

The signs and symptoms of compression neuropathy in HNPP are the same as those of the acquired type. HNPP can mimic the symptoms of carpal tunnel syndrome. (Tier 4) [2, 4]

In a study of 73 individuals (mean age 43 years; range 17 to 84 years) with HNPP that were followed at a single center over a 20-year period, six individuals (8%) experienced more than one episode before the diagnosis. (Tier 5) [10]

Date of Search: 07.15.2020

Reference List

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

2. Online Medelian Inheritance in Man, OMIM®. Johns Hopkins University, Baltimore, MD. NEUROPATHY, HEREDITARY, WITH LIABILITY TO PRESSURE PALSIES; HNPP. MIM: 162500: 2019 May 14. World Wide Web URL: http://omim.org.

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. 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

5. Dubourg O, Mouton P, Brice A, LeGuern E, Bouche P. Guidelines for diagnosis of hereditary neuropathy with liability to pressure palsies. Neuromuscul Disord. (2000) 10(0960-8966):206-8.

6. Robert-Varvat F, Jousserand G, Bouhour F, Vial C, Cintas P, Echaniz-Laguna A, Delmont E, Clavelou P, Chauplannaz G, Jomir L, Pereon Y, Leonard-Louis S, Manel V, Antoine JC, Lacour A, Camdessanche JP. Hereditary neuropathy with liability to pressure palsy in patients under 30 years old: Neurophysiological data and proposed electrodiagnostic criteria. Muscle Nerve. (2018) 57(1097-4598):217-221.

7. Hereditary neuropathy with liability to pressure palsies in childhood: Case series and literature update. Neuromuscul Disord.. (2015) Website: http://www.ncbi.nlm.nih.gov/books/NBK1392/

8. Sivera Mascaró R, García Sobrino T, Horga Hernández A, Pelayo Negro AL, Alonso Jiménez A, Antelo Pose A, Calabria Gallego MD, Casasnovas C, Cemillán Fernández CA, Esteban Pérez J, Fenollar Cortés M, Frasquet Carrera M, Gallano Petit MP, Giménez Muñoz A, Gutiérrez Gutiérrez G, Gutiérrez Martínez A, Juntas Morales R, Ciano-Petersen NL, Martínez Ulloa PL, Mederer Hengstl S, Millet Sancho E, Navacerrada Barrero FJ, Navarrete Faubel FE, Pardo Fernández J, Pascual Pascual SI, Pérez Lucas J, Pino Mínguez J, Rabasa Pérez M, Sánchez González M, Sotoca J, Rodríguez Santiago B, Rojas García R, Turon-Sans J, Vicent Carsí V, Sevilla Mantecón T. Clinical practice guidelines for the diagnosis and management of Charcot-Marie-Tooth disease. Neurologia (Engl Ed). (2024)

9. Mouton P, Tardieu S, Gouider R, Birouk N, Maisonobe T, Dubourg O, Brice A, LeGuern E, Bouche P. Spectrum of clinical and electrophysiologic features in HNPP patients with the 17p11.2 deletion. Neurology. (1999) 52(0028-3878):1440-6.

10. Luigetti M, Del Grande A, Conte A, Lo Monaco M, Bisogni G, Romano A, Zollino M, Rossini PM, Sabatelli M. Clinical, neurophysiological and pathological findings of HNPP patients with 17p12 deletion: a single-centre experience. J Neurol Sci. (2014) 341(1878-5883):46-50.

11. Gechev A, Kane NM, Koltzenburg M, Rao DG, van der Star R. Potential risks of iatrogenic complications of nerve conduction studies (NCS) and electromyography (EMG). Clin Neurophysiol Pract. (2016) 1(2467-981X):62-66.

12. Mora E, Smith EM, Donohoe C, Hertz DL. Vincristine-induced peripheral neuropathy in pediatric cancer patients. Am J Cancer Res. (2016) 6(2156-6976):2416-2430.