What are some diseases or genetic abnormalities caused by dominant genes? Why are severe dominant genetic diseases rarer than recessive ones?

Instance of dominant genetic diseases are, Huntington's disease (or Huntington's chorea), hypercholesterolemia, neurofibromatosis, polycystic kidney disease.

Early and Severe autosomal dominant diseases are rarer than recessive autosomal diseases because in this last group the affected allele may be hidden in the heterozygous individuals and transmitted to the offspring until undergoing homozygosity (actual manifestation of the disease). In the severe dominant diseases the heterozygous manifests the condition and often dies without having offspring (Some genetic diseases are of later manifestation, like Huntington disease; in these cases the incidence is higher because many individuals have children before knowing that they are carriers of the dominant gene).