Although WNT1 was originally identified as an essential regulator for midbrain and cerebellum development,9 several research groups reported recently that homozygous variants in WNT1 caused moderate-to-severe OI syndromes in patients, and heterozygous WNT1 variants resulted in early onset of osteoporosis,6,10-12 suggesting WNT1 as a key regulator for bone homeostasis. The gene discussed is WNT1; the disease is osteoporosis.