Ichthyosis is considered rare and appears to be breed specific, sometimes known as "fish scale" disease. It can resemble many other skin conditions such as allergies, dermatitis, and localized reactions. Most often present at birth, and can be painful. Symptoms include: thickened pads of his paws, irritated, flaking skin, may not itch or scab, also can cause thickened skin with scaly and greasy patches and flakes. This can cause water loss, as skin is unable to maintain moisture.
"Congenital, nonepidermolytic cornification disorders phenotypically resembling human autosomal recessive ichthyosis have been described in purebred dog breeds, including Jack Russell terrier (JRT) dogs. One cause of gene mutation important to humans and dogs is transposon insertions...Dogs were evaluated clinically, and skin samples were examined by light and electron microscopy. Phenotypic information and genotyping with a canine microsatellite marker suggested TGM1 to be a candidate gene. Genomic DNA samples and cDNA generated from epidermal RNA were examined. Consequences of the mutation were evaluated by Western blotting, quantitative reverse transcription-polymerase chain reaction (RT-PCR) and enzyme activity from cultured keratinocytes...Affected dogs had generalized severe hyperkeratosis. Histological examination defined laminated to compact hyperkeratosis without epidermolysis; ultrastructurally, cornified envelopes were thin. Affected dogs were homozygous for a 1980-bp insertion within intron 9 of TGM1. The sequence of the insertion was that of a canine LINE-1 element. Quantitative RT-PCR indicated a significant decrease in TGM1 mRNA in affected dogs compared with wild-type. TGM1 protein was markedly decreased on immunoblotting, and membrane-associated enzyme activity was diminished in affected dogs." [From Credille et al. 2009]
2009 Credille, KM., Minor, JS., Barnhart, KF., Lee, E., Cox, ML., Tucker, KA., Diegel, KL., Venta, PJ., Hohl, D., Huber, M., Dunstan, RW. : Transglutaminase 1-deficient recessive lamellar ichthyosis associated with a LINE-1 insertion in Jack Russell terrier dogs. Br J Dermatol 161:265-72, 2009. Pubmed reference: 19438474. DOI: 10.1111/j.1365-2133.2009.09161.x.