Heterotetramer of two type I and two type II keratins. Synthesis begins in the cortex 10-15 cell layers above the apex of the dermal papilla and ends abruptly in the middle of the cortex. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. There are two types of hair/microfibrillar keratin, I (acidic) and II (neutral to basic). Belongs to the intermediate filament family.