WFIKKN1 and Prader-Willi syndrome: Epithelial discoidin domain-containing receptor 1 (DDR1), WAP Kazal immunoglobulin Kunitz and NTR domain-containing protein 1 (WFIKKN1), and Growth/Differentiation Factor 8 (GDF-8), also known as myostatin, were significantly lower in female subjects with PWS (n = 29) compared to males (n = 24) (p < 0.05) (Table 2, and Figure 1).