Haemophilia, Cystic fibrosis, and Thalassemia are explicitly listed as Mendelian disorders (genetic disorders caused by mutation in a single gene) and are hereditary . Cretinism is described as a condition resulting from hypothyroidism (deficiency of thyroid hormones) during pregnancy, which leads to stunted growth and mental retardation in the baby . Therefore, unlike the others, it is primarily a hormonal deficiency disorder.