A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders are the most common, the term is mostly used when discussing disorders with a single genetic cause, either in a gene or chromosome. The mutation responsible can occur spontaneously before embryonic development, or it can be inherited from two parents who are carriers of a faulty gene or from a parent with the disorder. When the genetic disorder is inherited from one or both parents, it is also classified as a hereditary disease. Some disorders are caused by a mutation on the X chromosome and have X-linked inheritance. Very few disorders are inherited on the Y chromosome or mitochondrial DNA.
Macrocephaly is a condition in which circumference of the human head is abnormally large. It may be pathological or harmless, and can be a familial genetic characteristic. People diagnosed with macrocephaly will receive further medical tests to determine whether the syndrome is accompanied by particular disorders. Those with benign or familial macrocephaly are considered to have megalencephaly.
Ichthyosis vulgaris is a skin disorder causing dry, scaly skin. It is the most common form of ichthyosis, affecting around 1 in 250 people. For this reason it is known as common ichthyosis. It is usually an autosomal dominant inherited disease, although a rare non-heritable version called acquired ichthyosis exists.
Epidermolytic ichthyosis (EI), is a rare and severe form of ichthyosis that affects around 1 in 300,000 people. It is caused by a genetic mutation, and thus cannot be completely cured without some form of gene therapy.
Darier's disease (DAR) is an inherited skin disorder that presents with multiple greasy, crusting, thick brown bumps that merge into patches. It is an autosomal dominant disorder discovered by French dermatologist Ferdinand-Jean Darier.
A sebaceous cyst is a term commonly used to refer to either:
An epidermoid cyst or epidermal inclusion cyst is a benign cyst usually found on the skin. The cyst develops out of ectodermal tissue. Histologically, it is made of a thin layer of squamous epithelium.
Palmoplantar keratodermas are a heterogeneous group of disorders characterized by abnormal thickening of the stratum corneum of the palms and soles.
Ectodermal dysplasia (ED) is a group of genetic syndromes all deriving from abnormalities of the ectodermal structures. More than 150 different syndromes have been identified.
Lipomatosis is believed to be an autosomal dominant condition in which multiple lipomas are present on the body. Many discrete, encapsulated lipomas form on the trunk and extremities, with relatively few on the head and shoulders. In 1993, a genetic polymorphism within lipomas was localized to chromosome 12q15, where the HMGIC gene encodes the high-mobility-group protein isoform I-C. This is one of the most commonly found mutations in solitary lipomatous tumors but lipomas often have multiple mutations. Reciprocal translocations involving chromosomes 12q13 and 12q14 have also been observed within.
Greig cephalopolysyndactyly syndrome is a disorder that affects development of the limbs, head, and face. The features of this syndrome are highly variable, ranging from very mild to severe. People with this condition typically have one or more extra fingers or toes (polydactyly) or an abnormally wide thumb or big toe (hallux).
White sponge nevus (WSN) is an autosomal dominant condition of the oral mucosa. It is caused by a mutations in certain genes coding for keratin, which causes a defect in the normal process of keratinization of the mucosa. This results in lesions which are thick, white and velvety on the inside of the cheeks within the mouth. Usually, these lesions are present from birth or develop during childhood. The condition is entirely harmless, and no treatment is required.
Naegeli–Franceschetti–Jadassohn syndrome (NFJS), also known as chromatophore nevus of Naegeli and Naegeli syndrome, is a rare autosomal dominant form of ectodermal dysplasia, characterized by reticular skin pigmentation, diminished function of the sweat glands, the absence of teeth and hyperkeratosis of the palms and soles. One of the most striking features is the absence of fingerprint lines on the fingers.
Pachyonychia congenita is a rare group of autosomal dominant skin disorders that are caused by a mutation in one of five different keratin genes. Pachyonychia congenita is often associated with thickened toenails, plantar keratoderma, and plantar pain.
Monilethrix is a rare autosomal dominant hair disease that results in short, fragile, broken hair that appears beaded. It comes from the Latin word for necklace (monile) and the Greek word for hair (thrix). Hair becomes brittle, and breaks off at the thinner parts between the beads. It appears as a thinning or baldness of hair and was first described in 1897 by Walter Smith
Inflammatory Linear Verrucous Epidermal Nevus is a rare disease of the skin that presents as multiple, discrete, red papules that tend to coalesce into linear plaques that follow the Lines of Blaschko. The plaques can be slightly warty (psoriaform) or scaly (eczema-like). ILVEN is caused by somatic mutations that result in genetic mosaicism. There is no cure, but different medical treatments can alleviate the symptoms.
Eruptive vellus hair cysts are small lesions that occur most often in the chest wall, abdomen and extremities, often with a crusted surface. EVHC may occur randomly, or it can be inherited as an autosomal dominant trait; sporadic cases usually appear at 4–18 years of age. The cysts appear similar clinically to steatocystoma multiplex, as well as acneiform eruptions and milia. Histopathology is the basis of diagnosis. Retinoids, surgery, and lasers are used as treatment modalities.
Autosomal dominant porencephaly type I is a rare type of porencephaly that causes cysts to grow on the brain and damage to small blood vessels, which can lead to cognitive impairment, migraines, seizures, and hemiplegia or hemiparesis.
CYLD cutaneous syndrome (CCS) is the recently designated term for three rare inherited cutaneous adnexal tumor syndromes: multiple familial trichoepithelioma (MFT1), Brooke–Spiegler syndrome (BSS), and familial cylindromatosis (FC). Cutaneous adnexal tumors are a large group of skin tumors that consist of tissues that have differentiated towards one of the four primary adnexal structures found in normal skin: hair follicles, sebaceous sweat glands, apocrine sweat glands, and eccrine sweat glands. CCS tumors are hair follicle tumors.
