Pachyonychia Congenita: A group of inherited ectodermal dysplasias whose most prominent clinical feature is hypertrophic nail dystrophy resulting in PACHYONYCHIA. Several specific subtypes of pachyonychia congenita have been associated with mutations in genes that encode KERATINS.Nails, Malformed: Deformities in nail structure or appearance, including hypertrophy, splitting, clubbing, furrowing, etc. Genetic diseases such as PACHYONYCHIA CONGENITA can result in malformed nails.Keratin-6: A type II keratin found associated with KERATIN-16 or KERATIN-17 in rapidly proliferating squamous epithelial tissue. Mutations in gene for keratin-6A and keratin-6B have been associated with PACHYONYCHIA CONGENITA, TYPE 1 and PACHYONYCHIA CONGENITA, TYPE 2 respectively.Keratoderma, Palmoplantar: Group of mostly hereditary disorders characterized by thickening of the palms and soles as a result of excessive keratin formation leading to hypertrophy of the stratum corneum (hyperkeratosis).Keratin-16: A type I keratin expressed in a variety of EPITHELIUM, including the ESOPHAGUS, the TONGUE, the HAIR FOLLICLE and NAILS. Keratin-16 is normally found associated with KERATIN-6. Mutations in the gene for keratin-6 have been associated with PACHYONYCHIA CONGENITA, TYPE 1.Keratin-17: A type I keratin found associated with KERATIN-6 in rapidly proliferating squamous epithelial tissue. Mutations in the gene for keratin-17 have been associated with PACHYONYCHIA CONGENITA, TYPE 2.Ectodermal Dysplasia: A group of hereditary disorders involving tissues and structures derived from the embryonic ectoderm. They are characterized by the presence of abnormalities at birth and involvement of both the epidermis and skin appendages. They are generally nonprogressive and diffuse. Various forms exist, including anhidrotic and hidrotic dysplasias, FOCAL DERMAL HYPOPLASIA, and aplasia cutis congenita.Nail Diseases: Diseases of the nail plate and tissues surrounding it. The concept is limited to primates.Darier Disease: An autosomal dominantly inherited skin disorder characterized by warty malodorous papules that coalesce into plaques. It is caused by mutations in the ATP2A2 gene encoding SERCA2 protein, one of the SARCOPLASMIC RETICULUM CALCIUM-TRANSPORTING ATPASES. The condition is similar, clinically and histologically, to BENIGN FAMILIAL PEMPHIGUS, another autosomal dominant skin disorder. Both diseases have defective calcium pumps (CALCIUM-TRANSPORTING ATPASES) and unstable desmosomal adhesion junctions (DESMOSOMES) between KERATINOCYTES.Eyebrows: Curved rows of HAIR located on the upper edges of the eye sockets.Myotonia Congenita: Inherited myotonic disorders with early childhood onset MYOTONIA. Muscular hypertrophy is common and myotonia may impair ambulation and other movements. It is classified as Thomsen (autosomal dominant) or Becker (autosomal recessive) generalized myotonia mainly based on the inheritance pattern. Becker type is also clinically more severe. An autosomal dominant variant with milder symptoms and later onset is known as myotonia levior. Mutations in the voltage-dependent skeletal muscle chloride channel are associated with the disorders.Dyskeratosis Congenita: A predominantly X-linked recessive syndrome characterized by a triad of reticular skin pigmentation, nail dystrophy and leukoplakia of mucous membranes. Oral and dental abnormalities may also be present. Complications are a predisposition to malignancy and bone marrow involvement with pancytopenia. (from Int J Paediatr Dent 2000 Dec;10(4):328-34) The X-linked form is also known as Zinsser-Cole-Engman syndrome and involves the gene which encodes a highly conserved protein called dyskerin.Keratins: A class of fibrous proteins or scleroproteins that represents the principal constituent of EPIDERMIS; HAIR; NAILS; horny tissues, and the organic matrix of tooth ENAMEL. Two major conformational groups have been characterized, alpha-keratin, whose peptide backbone forms a coiled-coil alpha helical structure consisting of TYPE I KERATIN and a TYPE II KERATIN, and beta-keratin, whose backbone forms a zigzag or pleated sheet structure. alpha-Keratins have been classified into at least 20 subtypes. In addition multiple isoforms of subtypes have been found which may be due to GENE DUPLICATION.Glossitis: Inflammation of the tongue.Nails: The thin, horny plates that cover the dorsal surfaces of the distal phalanges of the fingers and toes of primates.Skin Diseases, Genetic: Diseases of the skin with a genetic component, usually the result of various inborn errors of metabolism.Keratins, Type II: A keratin subtype that includes keratins that are generally larger and less acidic that TYPE I KERATINS. Type II keratins combine with type I keratins to form keratin filaments.Mutation, Missense: A mutation in which a codon is mutated to one directing the incorporation of a different amino acid. This substitution may result in an inactive or unstable product. (From A Dictionary of Genetics, King & Stansfield, 5th ed)Arthrogryposis: Persistent flexure or contracture of a joint.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Phenotype: The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.