SPRY4 and cartilage-hair hypoplasia: DUSP6 (Dual Specificity Phosphatase 6; chr 12q21.33) and SPRY4 (Sprouty RTK Signaling Antagonist 4; chr 5q31.1) are repressors of the FGF8/FGFR1-activated MAPK cascade and pathogenic variants were found in patients with either normosmic CHH and KS together with hearing loss [214].