It's a neurological disorder caused by genetic abnormalities that show up in specialty morphs called the "Enigma" morph. So remember how I said that the specialty breeding to get Flame's colors and translucence caused his neurological disorder? Like a form of Inbreeding? Same exact thing with Enigma syndrome.
Here's an Excellent Article on it. From that article:
What is ES?
Enigma Syndrome (ES) is a neurological disorder that affects the balance and cognition of leopard geckos. The severity of this genetic mutation varies from relatively mild symptoms, such as: ‘star gazing’, head tilting, and occasional circling to debilitating effects such as: seizures, ‘death rolls’, and incessant circling in place (similar to diagnostic symptoms in autistic individuals). Affected individuals with the same mutation will manifest different degrees of severity of this disorder, because of environmental factors and their individual genotype.
Environmental stressors such as bunking with an aggressive cage-mate, being vacuumed up by a distracted breeder, or just the normal rigors of shipping can be enough trauma to activate this syndrome. Enigma Syndrome is a misnomer, as all morphs are susceptible to this disorder; however, it is more prevalent in the Enigma morph. Balance disorders seen in non-enigma morphs may, in fact, be one and the same disorder.
Stress activates the neurological disorder which is why the female is worse when I'm cleaning her wounds and such. It can't be fixed. She'll always have it and we can only lessen it by keeping her in a calm, stress-free environment.
UGH. It reminds me of something I've said many times-- just because you CAN breed certain morphs doesn't mean you SHOULD!
I have a "Fancy" bearded dragon morph that has constant tremors. I have a "Specialty" morph leopard gecko that has serious balance disorders. I have a purebred Maltese dog that has terrible hips and knees because of her specific genes. Genetic specificity (I made that up just now and don't know if it's an actual thing) can create a whole host of problems. It's like diving in the shallow end of the gene pool. :(