In a recent natural history analysis of MSD, Adang et al7 found characteristic constellations of “early developmental delay, ichthyosis, hepatosplenomegaly, and hearing loss.” Biallelic SUMF1 mutations labeled as “mild” were associated with onset >1 months of age, achievement of independent ambulation and multiword sentences, slower regression, and longer survival.7 Here, SUMF1 is linked to Global developmental delay.