Exploring human plasma proteomic variations in mucolipidosis type IV

Mucolipidosis IV (MLIV) is an autosomal-recessive pediatric disease that leads to motor and cognitive deficits and loss of vision. It is caused by loss of function of the lysosomal channel transient receptor potential mucolipin-1, TRPML1, and is associated with an early brain phenotype consisting of glial reactivity, hypomyelination, and lysosomal abnormalities. Although the field is approaching the first translationally relevant therapy, we currently lack a molecular signature of disease that can be used to detect therapeutic efficacy. Here, we analyzed 7,322 proteins in the plasma proteome from 17 MLIV patients and 37 controls and compared protein profiles with clinical measures of disease severity (motor function, muscle tone, and age). We found a decrease in neuronal proteins and an increase in muscle proteins in MLIV, consistent with neuronal dysfunction and muscle pathology observed in patients. Reduced synaptic proteins (e.g., GABARAP) best correlated with disease severity. Comparing the MLIV plasma proteome to the brain proteome from the MLIV mouse model identified shared alterations in 45 proteins, including upregulated proteins related to lysosomal function (e.g., ACTN2, GLB1) and downregulated proteins related to myelination (e.g., TPPP3, CNTN2). These data indicate that peripheral blood plasma protein signatures mirror changes found in the MLIV brain.