Keratosis follicularis, also known as Darier disease (DD) or Darier-White disease, is an autosomal dominantly inherited genodermatosis characterized by greasy hyperkeratotic papules in seborrheic regions, nail abnormalities, and mucous membrane changes. See the images below. The disease was first reported independently by Darier and White in 1889. White was first to recognize the genetic nature of keratosis follicularis (Darier disease) by noticing that a mother and her daughter were affected.
Mutations in the gene ATP2A2 cause keratosis follicularis (Darier disease). ATP2A2, located on 12q23-24.1, encodes the sarcoplasmic/endoplasmic reticulum Ca2+ -ATP isoform 2 protein (SERCA2), which is a calcium pump.  This pump maintains a low cytoplasmic Ca2+ level by actively transporting calcium ions from the cytosol into the lumen of the endoplasmic reticulum. Although more than 120 familial and sporadic mutations in ATP2A2 have been identified in keratosis follicularis (Darier disease) patients, attempts at genotype-phenotype correlation have not been successful.
Family members with confirmed identical ATP2A2 mutations can exhibit differences in the clinical severity of disease, suggesting that other genes or environmental factors affect the expression of keratosis follicularis (Darier disease). [2, 3] A wide variety of ATP2A2 mutations in Darier disease have been identified. [4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
The mechanisms by which specific ATP2A2 mutations impact the function of the ATP2A2 protein have been investigated using an in vitro model.  Investigators transfected a fibroblast cell line with 51 different mutations seen in keratosis follicularis (Darier disease) pedigrees. The investigators found that the resultant transfected cells showed defects in ATP2A2 protein expression (15 mutants), ATP hydrolysis (29 mutants), calcium transport (4 mutants), and calcium binding and kinetics (3 mutants). In a different study, in which researchers systematically analyzed mutations identical to those found in patients with Darier disease, mutant SERCA2 protein aggregates were found to cause stress to the endoplasmic reticulum, subsequently inducing cell apoptosis.  Thus, diverse biochemical mechanisms are responsible for altered protein function.
Although expressivity is variable, penetrance of keratosis follicularis (Darier disease) is high, estimated at 95%. Because the disease-causing mutations in ATP2A2 affect functional domains of the gene, the mechanism of autosomal dominant transmission is believed to be haploinsufficiency, in which a single wild-type functioning ATP2A2 is insufficient to prevent disease. No unique phenotype for genetic homozygotes has been reported.
Abnormal keratinocyte-keratinocyte adhesion and aberrant epidermal keratinization are the primary histologic features of keratosis follicularis (Darier disease). Electron microscopy reveals loss of desmosomes (epithelial intercellular junctions formed by membrane and submembrane protein complexes), breakdown of desmosome-keratin intermediate filament attachment, and perinuclear aggregates of keratin intermediate filaments. The mechanism by which decreased activity of the SERCA2 calcium pump leads to these changes is still under investigation.  However, a significant correlation exists between the clinical presentation of keratosis follicularis (Darier disease) and the intensity of histologic features. 
Some studies of keratosis follicularis (Darier disease) have suggested that alterations in calcium regulation may affect the synthesis, folding, or trafficking of desmosomal proteins.  In particular, studies have revealed that keratosis follicularis (Darier disease) keratinocytes displayed abnormal trafficking of the desmosomal protein desmoplakin and abnormal expression of cytokeratins 10 and 14. [25, 26] A recent study shows that SERCA2-controlled Ca²+ -dependent keratinocyte adhesion and differentiation is mediated via the sphingolipid pathway. 
Alternatively, another hypothesis, based on a canine model of keratosis follicularis (Darier disease), is that keratosis follicularis (Darier disease) calcium dysregulation leads to impaired control of cell cycle checkpoints, leading to increased epidermal sensitivity to skin trauma and subsequent keratinocyte apoptosis.
Two particular ATP receptors have been reported to abnormally localize in vivo in keratosis follicularis(Darier disease) and are speculated to play a role in apoptosis as well as abnormal calcium signaling.  More recently, Darier keratinocytes were found to display a constitutive endoplasmic reticulum stress response, with immature adherens junctions and desmosomes, which results in decreased intercellular adhesion strength. 
Remarkably, an orphan drug, the α-glucosidase inhibitor miglustat, restores mature adherens junctions and desmosomes in Darier keratinocytes and increases adhesion strength. The observation that miglustat is able to restore proper localization to the plasma membrane of nonmutated proteins retained in the endoplasmic reticulum supports a misfolding mechanism. 
Keratosis follicularis (Darier disease) occurs worldwide. The prevalence of keratosis follicularis (Darier disease) has been estimated to range from 1 case in 30,000 population in Scotland to 1 case in 100,000 population in Denmark.
Males and females are equally affected by keratosis follicularis (Darier disease).
Keratosis follicularis (Darier disease) most commonly manifests from age 6-20 years; however, patients have presented as early as age 4 years and as late as age 70 years. Notably, the first case of congenital keratosis follicularis (Darier disease) was diagnosed by biopsy in a child with a significant positive family history for keratosis follicularis (Darier disease), in which at least the 3 proceeding generations of family members were affected. 
Patients with keratosis follicularis (Darier disease) experience pruritus and sometimes pain in the affected skin areas. Psychosocial consequences from the appearance and odor of the lesions also constitute the major morbidity of keratosis follicularis (Darier disease). A serious complication associated with keratosis follicularis (Darier disease) is increased susceptibility to cutaneous bacterial and viral infections, in particular herpes simplex virus and poxvirus infections. Initial misdiagnosis of keratosis follicularis (Darier disease) may lead to undertreatment of such infections and may lead to fatal outcomes. [30, 31] However, overall, patients with keratosis follicularis (Darier disease) have a life expectancy similar to that of the general population.
Neuropsychiatric abnormalities such as epilepsy, mental impairment, schizophrenia,  and mood disorders have been associated with keratosis follicularis (Darier disease). Several national studies suggest that genetic variability within the ATP2A2 gene that causes Darier disease also confers susceptibility for a number of neuropsychiatric disorders,  including bipolar disorder,  intellectual disability, and subclinical impairments in cognitive ability. 
What would you like to print?