A comparative phenotypic analysis of a heterogeneous PMP22 cohort presenting with persistent toe-walking versus...

The Peripheral Myelin Protein 22 (PMP22) gene plays a central role in peripheral nerve myelination, and dosage alterations (deletion, duplication, or point mutation) are established causes of hereditary neuropathies such as Charcot-Marie-Tooth disease type 1 A (CMT1A), CMT1E, and Hereditary Neuropathy with Liability to Pressure Palsies (HNPP). However, its potential contribution to atypical developmental motor phenotypes such as persistent toe-walking (PTW) has not been systematically explored.

To characterize the phenotypic spectrum of pediatric PMP22 variant carriers presenting with PTW and to compare their clinical features with those of established PMP22-related neuropathies.

This retrospective study analyzed 22 children with PMP22 variants (pathogenic, likely pathogenic, or of uncertain significance) identified through a targeted 49-gene next-generation sequencing panel. Detailed phenotypic data were collected across five clinical domains-genetic, developmental, gait and musculoskeletal, neurological, and associated comorbidities-and compared to standardized phenotype frequencies for CMT1A, CMT1E, and HNPP derived from Orphanet and the Human Phenotype Ontology (HPO) databases.

Persistent tip-toe gait was universal, accompanied by pes cavus, lumbar hyperlordosis, tremor, and hyporeflexia. Speech and language difficulties were reported in 45 % of cases, and a family history of toe-walking in 40 %. Additional muscle symptoms and neurological findings were reported, developmental disorders were also reported.

Children carrying PMP22 variants with PTW exhibit a distinct phenotype differing from classic demyelinating neuropathies. The findings suggest that a subset of idiopathic toe-walking cases may represent a developmental manifestation within the PMP22-related disease spectrum, highlighting the value of genetic testing in reevaluating gait disorders of uncertain etiology.