Comparison of two clinical motor scales in individuals with giant axonal neuropathy (GAN)

Giant axonal neuropathy (GAN) is a rare autosomal recessive neurodegenerative disease that affects the peripheral and the central nervous system. Clinical symptoms include neuropathy, ataxia, dysphagia, dysarthria, and distal and later proximal muscle weakness. There are currently no approved treatments for GAN. It is important to identify appropriate assessment tools to measure function in preparation for future interventional trials, such as gene transfer. The only recent natural history study to include functional measures in subjects with GAN uses the Gross Motor Function Measure (GMFM). The goal of this study is to compare the GMFM to the Motor Function Measure (MFM) in people with GAN. The GMFM was developed and validated in people with cerebral palsy; the MFM was developed and validated in people with progressive neuromuscular diseases. Our study included seven subjects (5 females) with a mean age of 8.8 years. All subjects completed the GMFM and MFM 32 except one young child who was assessed using the MFM 20 (version of the MFM 32 validated in individuals 2–6 years of age). Spearman's rho correlations were used to compare the tests in three ways: (1) The D2 (axial and proximal motor function) domain of the MFM with the combined domains A and B (lying, rolling, and sitting) of the GMFM. (2) The D1 (standing and transfers) of the MFM and the combined domains D and E (standing, walking, running, and jumping) of the GMFM. (3) Total percentages for both the GMFM and the MFM. There was a strong correlation between the MFM (D2) and the GMFM (A + B) domains, rs = 1.0, p < .05, MFM (D1) and GMFM (D + E) domains rs = .964, p < .05, and between the total percentages for both the GMFM and the MFM, rs = 1.0, p < .05. We conclude that one test alone may be used to capture gross motor function in subjects with GAN. Given that the MFM is validated in subjects with progressive neuromuscular diseases, we recommend using the MFM for this population.