Natural history of Type 2 and 3 spinal muscular atrophy: 2‐year NatHis‐SMA study

Methods: Patients with Type 2 and 3 SMA (N = 81) with varied functional abilities (sitters, nonsitters, nonambulant, and ambulant) who were not receiving disease‐modifying treatment were assessed over 24 months: motor function (Motor Function Measure [MFM]), upper limb strength (MyoGrip, MyoPinch), upper limb activity (ActiMyo®), quantitative magnetic resonance imaging (fat fraction [FF] mapping and contractile cross‐sectional area [C‐CSA]), pulmonary function (forced vital capacity [FVC], peak cough flow, maximum expiratory pressure, maximum inspiratory pressure, and sniff nasal inspiratory pressure), and survival of motor neuron (SMN) protein levels. Outcomes assessed during the study include motor function (MFM), upper limb strength (MyoGrip, MyoPinch), upper limb activity (ActiMyo®), quantitative magnetic resonance imaging (MRI) (FF mapping and muscle contractile cross‐sectional area [C‐CSA]), pulmonary tests (forced vital capacity [FVC], peak cough flow [PCF], maximum expiratory pressure [MEP], maximum inspiratory pressure [MIP], and sniff nasal inspiratory pressure [SNIP]), and measurement of blood SMN protein levels. Methods section, MRI muscle assessment subsection: FF maps were derived from quantitative water‐fat imaging obtained using a 3‐point Dixon 3D gradient echo sequence; the Dixon‐based regions of interest were used in combination with the FF mapping to provide the C‐CSA, as previously described.19 These assessments were carried out in one study site with a limited number of patients.