The Lambert type of ichthyosis hystrix (IHL) is characterized by normal skin at birth that develops striking spiny hyperkeratotic lesions within a few months. There is sparing of the face, palms, and soles, and affected individuals do not experience blistering. Marked improvement of lesions during the summer months has also been observed in some patients. Ultrastructurally, binuclear cells and tonofilament shells surrounding the nucleus in upper keratinocytes are observed (summary by Penrose and Stern, 1958; Wang et al., 2007; Wang et al., 2016). Another form of ichthyosis hystrix, the Curth-Macklin type (IHCM; 146590), includes severe palmoplantar keratoderma among its features and is caused by mutation in the KRT1 (139350) gene.

Striate palmoplantar keratoderma belongs to a group of skin diseases in which there is thickening of the skin on the palms and soles. The striate form is characterized by longitudinal hyperkeratotic lesions extending the length of each finger to the palm, and hyperkeratotic lesions are restricted to regions of the body where pressure and abrasion are greatest (summary by Hunt et al., 2001). Patients with diffuse or focal forms of keratoderma associated with mutation in the DSG1 gene have also been reported (Keren et al., 2005; Milingou et al., 2006). Genetic Heterogeneity of Keratosis Palmoplantaris Striata Type II PPKS (PPKS2; 612908) is caused by mutation in the DSP gene (125647) on chromosome 6. Type III PPKS (PPKS3; 607654) is caused by mutation in the keratin-1 gene (KRT1; 139350) on chromosome 12q. For a general phenotypic description and a discussion of genetic heterogeneity of palmoplantar keratoderma (PPK), see epidermolytic PPK (144200). Nitoiu et al. (2014) reviewed desmosome biology in cardiocutaneous syndromes and inherited skin disease, including discussion of the involvement of the DSG1 and DSP genes.

Palmoplantar keratoderma-XX sex reversal-predisposition to squamous cell carcinoma syndrome is characterised by sex reversal in males with a 46, XX (SRY-negative) karyotype, palmoplantar hyperkeratosis and a predisposition to squamous cell carcinoma. To date, five cases (four of whom were brothers) have been described. The aetiology is unknown.

Autosomal recessive congenital ichthyosis (ARCI) is a heterogeneous group of disorders of keratinization characterized primarily by abnormal skin scaling over the whole body. These disorders are limited to skin, with approximately two-thirds of patients presenting severe symptoms. The main skin phenotypes are lamellar ichthyosis (LI) and nonbullous congenital ichthyosiform erythroderma (NCIE), although phenotypic overlap within the same patient or among patients from the same family can occur (summary by Fischer, 2009). Neither histopathologic findings nor ultrastructural features clearly distinguish between NCIE and LI. In addition, mutations in several genes have been shown to cause both lamellar and nonbullous ichthyosiform erythrodermal phenotypes (Akiyama et al., 2003). At the First Ichthyosis Consensus Conference in Soreze in 2009, the term 'autosomal recessive congenital ichthyosis' (ARCI) was designated to encompass LI, NCIE, and harlequin ichthyosis (ARCI4B; 242500) (Oji et al., 2010). NCIE is characterized by prominent erythroderma and fine white, superficial, semiadherent scales. Most patients present with collodion membrane at birth and have palmoplantar keratoderma, often with painful fissures, digital contractures, and loss of pulp volume. In half of the cases, a nail dystrophy including ridging, subungual hyperkeratosis, or hypoplasia has been described. Ectropion, eclabium, scalp involvement, and loss of eyebrows and lashes seem to be more frequent in NCIE than in lamellar ichthyosis (summary by Fischer et al., 2000). In LI, the scales are large, adherent, dark, and pigmented with no skin erythema. Overlapping phenotypes may depend on the age of the patient and the region of the body. The terminal differentiation of the epidermis is perturbed in both forms, leading to a reduced barrier function and defects of lipid composition in the stratum corneum (summary by Lefevre et al., 2006). In later life, the skin in ARCI may have scales that cover the entire body surface, including the flexural folds, and the scales are highly variable in size and color. Erythema may be very mild and almost invisible. Some affected persons exhibit scarring alopecia, and many have secondary anhidrosis (summary by Eckl et al., 2005). For a discussion of genetic heterogeneity of autosomal recessive congenital ichthyosis, see ARCI1 (242300).

Nagashima-type palmoplantar keratoderma is an autosomal recessive nonsyndromic diffuse palmoplantar keratosis, first described by Nagashima (1977) in the Japanese literature. It is characterized by well-demarcated diffuse erythematous hyperkeratosis that extends onto the dorsal surfaces of the palms and feet and the Achilles tendon area. Involvement of the elbows and knees has also been reported, and there is a high frequency of hyperhidrosis on the palms and soles. In contrast to other types of transgressive diffuse hyperkeratosis such as mal de Meleda (248300), PPKN shows only mild hyperkeratosis that is nonprogressive after the second decade and does not involve flexion contractures or constricting bands (summary by Kubo et al., 2013). For a discussion of phenotypic and genetic heterogeneity of palmoplantar keratoderma, see epidermolytic PPK (144200).