SPP1 genotype is a determinant of disease severity in Duchenne muscular dystrophy

Abstract

Objective: Duchenne muscular dystrophy (DMD) is the most common single-gene lethal disorder. Substantial patient-patient variability in disease onset and progression and response to glucocorticoids is seen, suggesting genetic or environmental modifiers.

Methods: Two DMD cohorts were used as test and validation groups to define genetic modifiers: a Padova longitudinal cohort (n = 106) and the Cooperative International Neuromuscular Research Group (CINRG) cross-sectional natural history cohort (n = 156). Single nucleotide polymorphisms to be genotyped were selected from mRNA profiling in patients with severe vs mild DMD, and genome-wide association studies in metabolism and polymorphisms influencing muscle phenotypes in normal volunteers were studied.

Results: Effects on both disease progression and response to glucocorticoids were observed with polymorphism rs28357094 in the gene promoter of SPP1 (osteopontin). The G allele (dominant model; 35% of subjects) was associated with more rapid progression (Padova cohort log rank p = 0.003), and 12%-19% less grip strength (CINRG cohort p = 0.0003).

Conclusions: Osteopontin genotype is a genetic modifier of disease severity in Duchenne dystrophy. Inclusion of genotype data as a covariate or in inclusion criteria in DMD clinical trials would reduce intersubject variance, and increase sensitivity of the trials, particularly in older subjects.

Figure 1. Retrospective mRNA profiling of muscle biopsies from patients with Duchenne muscular dystrophy (DMD) showing mild vs severe clinical course

(A) Component 1 (X-axis) and component 3 (Y-axis) plot of the correspondence analysis. Component 3 is seen to separate patients with DMD into 2 groups (yellow: 1,839, 3,368, 2,064; blue: 1,456, 3,639) corresponding to mild (yellow) vs severe (blue) clinical progression. (B) Bootstrap Pearson clustering analysis of the patients. Clustering of 1,456 and 3,639 patients is 100% bootstrap supported and is separated by the second cluster (3,668, 2,064, 1,839) linked to the first by a node presenting 0%–50% bootstrap supporting score. (C) Patients' bootstrap clusterization considering differentially expressed genes between the 2 patient groups. Gene expression values are expressed in log scale ratio relating to a common RNA control pool (log₂ DMD patient/control pool). Right arrows highlight SSP1. All cluster tree presents the yellow/blue upper bar representing the subdivision of the patients with DMD in late loss of ambulation (yellow) and early loss of ambulation (red).

Figure 2. SPP1 genotype is associated with decreased strength in steroid-treated patients with Duchenne muscular dystrophy

Shown is the association of SPP1 genotype with muscle strength (grip quantitative muscle testing) in the Cooperative International Neuromuscular Research Group cross-sectional cohort. The strongest association with strength was seen in steroid-treated, nonambulatory patients.

Figure 3. SPP1 genotype is associated with greater severity of progression in Duchenne muscular dystrophy (DMD)

The proportion of patients with DMD in the Padova cohort remaining ambulatory at the specific age noted is shown (n = 106). The GT/GG genotype is associated with more rapid progression.