HRAS Gene

Costello syndrome is a disorder that affects many parts of the body. This condition is characterized by delayed development and intellectual disability, loose folds of skin (which are especially noticeable on the hands and feet), unusually flexible joints, and distinctive facial features including a large mouth with full lips. Heart problems are common, including an abnormal heartbeat (arrhythmia), structural heart defects, and a type of heart disease that enlarges and weakens the heart muscle (hypertrophic cardiomyopathy). Infants with Costello syndrome may be larger than average at birth, but most have difficulty feeding and grow more slowly than other children. People with this condition have relatively short stature and may have reduced growth hormone levels. Other signs and symptoms of Costello syndrome can include tight Achilles tendons (which connect the calf muscles to the heel), weak muscle tone (hypotonia), a structural abnormality of the brain called a Chiari I malformation, skeletal abnormalities, dental problems, and problems with vision.

Beginning in early childhood, people with Costello syndrome are at an increased risk of developing certain cancerous and noncancerous tumors. The most common noncancerous tumors associated with this condition are papillomas, which are small, wart-like growths that usually develop around the nose and mouth or near the anus. The most common cancerous tumor associated with Costello syndrome is a childhood cancer called rhabdomyosarcoma, which begins in muscle tissue. Neuroblastoma, a tumor that arises in developing nerve cells, also has been reported in children and adolescents with this syndrome. In addition, some teenagers with Costello syndrome have developed transitional cell carcinoma, a form of bladder cancer that is usually seen in older adults.

The signs and symptoms of Costello syndrome overlap significantly with those of two other genetic conditions, cardiofaciocutaneous syndrome (CFC syndrome) and Noonan syndrome. In affected infants, it can be difficult to tell the three conditions apart based on their physical features. However, the conditions can be distinguished by their genetic cause and by specific patterns of signs and symptoms that develop later in childhood.

An epidermal nevus (plural: nevi) is an abnormal, noncancerous (benign) patch of skin caused by an overgrowth of cells in the outermost layer of skin (epidermis). Epidermal nevi are typically seen at birth or develop in early childhood. Affected individuals have one or more nevi that vary in size.

There are several types of epidermal nevus that are defined in part by the type of epidermal cell involved. The epidermis is composed primarily of a specific cell type called a keratinocyte. One group of epidermal nevi, called keratinocytic or nonorganoid epidermal nevi, includes nevi that involve only keratinocytes. Keratinocytic epidermal nevi are typically found on the torso or limbs. They can be flat, tan or brown patches of skin or raised, velvety patches. As affected individuals age, the nevi can become thicker and darker and develop a wart-like (verrucous) appearance. Often, keratinocytic epidermal nevi follow a pattern on the skin known as the lines of Blaschko. The lines of Blaschko, which are normally invisible on skin, are thought to follow the paths along which cells migrate as the skin develops before birth. Keratinocytic epidermal nevi are also known as linear epidermal nevi or verrucous epidermal nevi, based on characteristics of their appearance.

Other types of epidermal nevi involve additional types of epidermal cells, such as the cells that make up the hair follicles, the sweat glands, or the sebaceous glands (glands in the skin that produce a substance that protects the skin and hair). These nevi comprise a group called organoid epidermal nevi. A common type of organoid epidermal nevus is called nevus sebaceous. Nevi in this group are waxy, yellow-orange patches of skin, usually on the scalp or face. The patch is typically hairless, leaving a distinct region of baldness (alopecia). Similar to keratinocytic epidermal nevi, nevi sebaceous can become thicker and more verrucous over time. In about one-quarter of people with a nevus sebaceous, a tumor forms in the same region as the nevus. The tumor is usually benign, although rarely cancerous (malignant) tumors develop.

Some affected individuals have only an epidermal nevus and no other abnormalities. However, sometimes people with an epidermal nevus also have problems in other body systems, such as the brain, eyes, or bones. In these cases, the affected individual has a condition called an epidermal nevus syndrome. There are several different epidermal nevus syndromes characterized by the type of epidermal nevus involved.

Giant congenital melanocytic nevus is a skin condition characterized by an abnormally dark, noncancerous skin patch (nevus) that is composed of pigment-producing cells called melanocytes. It is present from birth (congenital) or is noticeable soon after birth. The nevus may be small in infants, but it will usually grow at the same rate the body grows and will eventually be at least 40 cm (15.75 inches) across. The nevus can appear anywhere on the body, but it is more often found on the trunk or limbs. The color ranges from tan to black and can become darker or lighter over time. The surface of a nevus can be flat, rough, raised, thickened, or bumpy; the surface can vary in different regions of the nevus, and it can change over time. The skin of the nevus is often dry and prone to irritation and itching (dermatitis). Excessive hair growth (hypertrichosis) can occur within the nevus. There is often less fat tissue under the skin of the nevus; the skin may appear thinner there than over other areas of the body.

People with giant congenital melanocytic nevus may have more than one nevus (plural: nevi). The other nevi are often smaller than the giant nevus. Affected individuals may have one or two additional nevi or multiple small nevi that are scattered over the skin; these are known as satellite or disseminated nevi.

Affected individuals may feel anxiety or emotional stress due to the impact the nevus may have on their appearance and their health. Children with giant congenital melanocytic nevus can develop emotional or behavior problems.

Some people with giant congenital melanocytic nevus develop a condition called neurocutaneous melanosis, which is the presence of pigment-producing skin cells (melanocytes) in the tissue that covers the brain and spinal cord. These melanocytes may be spread out or grouped together in clusters. Their growth can cause increased pressure in the brain, leading to headache, vomiting, irritability, seizures, and movement problems. Tumors in the brain may also develop.

Individuals with giant congenital melanocytic nevus have an increased risk of developing an aggressive form of skin cancer called melanoma, which arises from melanocytes. Estimates vary, but it is generally thought that people with giant congenital melanocytic nevus have a 5 to 10 percent lifetime risk of developing melanoma. Melanoma commonly begins in the nevus, but it can develop when melanocytes that invade other tissues, such as those in the brain and spinal cord, become cancerous. When melanoma occurs in people with giant congenital melanocytic nevus, the survival rate is low.

Other types of tumors can also develop in individuals with giant congenital melanocytic nevus, including soft tissue tumors (sarcomas), fatty tumors (lipomas), and tumors of the nerve cells (schwannomas).