Illustration of a molecule of the BLM DNA (deoxyribonucleic acid) helicase. Helicases are enzymes that unwind and separate the two strands of a DNA molecule. Correct separation of the strands is needed for replication, transcription, translation and repair. Mutations in the BLM helicase cause Bloom syndrome, a rare inherited condition that leads to short stature, rashes on exposure to sunlight and a greatly increased risk of cancer.