Common ichthyosis ("ichthyosis vulgaris") produces dry skin and (if you look closely), alligator-like pattern of scales, mostly on the extremities.

The autosomal dominant form of common ichthyosis is caused by defective synthesis of filaggrin, the histidine-rich protein of keratohyalin granules. For some reason, the desmosomes stay intact longer than they should, delaying the shedding of the dead epidermal cells. This semi-disease is extremely common, with 1 person in 250 affected.

The X-linked recessive form is caused by lack of steroid sulfatase ("arylsulfatase C"), which is responsible for the breakdown of the cholesteryl sulfate glue that helps hold skin cells together.
* If for some reason you want to distinguish these two entities, the autosomal dominant form spares the flexural creases, while the recessive form involves them. We can tell on biopsy too.
The more severe lamellar ichthyosis is a mix of genetic diseases, including people with defective K1 or K10 keratins, and people with defective transglutaminases