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Focal dermal hypoplasia is a genetic disorder that primarily affects the skin, skeleton, eyes, and face. The skin abnormalities are present from birth and can include streaks of very thin skin (dermal hypoplasia), cutis aplasia, and telangiectases. They also may abnormalities in the nails, hands, and feet. Some of the eye findings present may include small eyes (microphthalmia), absent or severely underdeveloped eyes (anophthalmia), and problems with the tear ducts. People with focal dermal hypoplasia may also have distinctive facial features such as a pointed chin, small ears, notched nostrils, and a slight difference in the size and shape of the right and left sides of the face (facial asymmetry). Most individuals with this condition are female. Males usually have milder signs and symptoms than females. Although intelligence is typically unaffected, some individuals have intellectual disability. This condition is caused by mutations in the PORCN gene and is inherited in an X-linked dominant manner. Most cases of focal dermal hypoplasia in females result from new mutations in the PORCN gene and occur in people with no history of the disorder in their family. When focal dermal hypoplasia occurs in males, it always results from a new mutation in this gene that is not inherited. Treatment is based on the signs and symptoms present in the person; however, care usually involves a team of specialists, including dermatologists, otolaryngologist, physical/occupational therapists, and hand surgeons.
Source: GARD Last updated on 05-01-20
Focal dermal hypoplasia is usually evident from birth and primarily affects the skin, skeleton, eyes, and face. The signs and symptoms of vary widely, although almost all affected individuals have skin abnormalities.
Some of the skin findings include streaks of very thin skin (dermal hypoplasia), yellowish-pink nodules of fat under the skin, areas where the top layers of skin are absent (cutis aplasia), telangiectases, and streaks of slightly darker or lighter skin. These skin features can cause pain, itching, irritation, or lead to skin infections. With age, most develop wart-like growths, called papillomas, around the nostrils, lips, anus, and female genitalia. They may also be present in the throat, specifically in the esophagus or larynx, and can cause problems with swallowing, breathing, or sleeping. Other features include small, ridged fingernails and toenails as well as sparse, brittle or absent scalp hair.
The skeleton is usually affected as well. Many individuals have hand and foot abnormalities, including missing fingers or toes (oligodactyly), webbed or fused fingers or toes (syndactyly), and a deep split in the hands or feet with missing fingers or toes and fusion of the remaining digits (ectrodactyly). X-rays can show streaks of altered bone density, called osteopathia striata, which usually do not cause symptoms.
Eye abnormalities are common and can include microphthalmia and anopthalmia as well as problems with the tear ducts. The retina or the optic nerve can also be incompletely developed, which can result in a gap or split in these structures (coloboma). Some of these eye abnormalities do not impair vision, while others can lead to low vision or blindness.
People with focal dermal hypoplasia often have distinctive, but subtle facial features such as a pointed chin, small ears, notched nostrils, and a slight difference in the size and shape of the right and left sides of the face (facial asymmetry). Some individuals may have a cleft lip and/or palate.
About half of those with focal dermal hypoplasia have teeth abnormalities of their teeth, especially of the enamel (the hard, white material that forms the protective outer layer of each tooth). Less commonly, kidney and gastrointestinal abnormalities are present. The kidneys may be fused together, which can lead to kidney infections. The main gastrointestinal abnormality that is seen is an omphalocele.
Last updated on 05-01-20
Focal dermal hypoplasia is caused by mutations in the PORCN gene and is inherited in an X-linked dominant manner. Many cases of focal dermal hypoplasia result from a new mutation and occur in people with no history of the disorder in their family For a woman affected with focal dermal hypoplasia, the theoretical risk of passing the mutation to each of her offspring is 50%; however, many males with this condition do not survive. In addition, there are cases in which a woman may have the focal dermal hypoplasia mutation in some but not all of her egg cells, a condition known as germline mosaicism. In this case the risk of passing along the mutation may be as high as 50% depending on the level of mosaicism. Males with focal dermal hypoplasia typically have the mutation in some but not all of their cells. The risk that a male with FDH will pass the condition on to his daughters may be as high as 100%; men do not pass this condition on to their sons. We recommend discussing specific concerns with a genetics professional, who can help you understand how this condition might be inherited in your family. Click on the following link for resources for finding a genetics professional.
Last updated on 05-01-20
Females have two X chromosomes, while males have one X chromosome and one Y chromosome. Early in female embryonic development, one of the two X chromosomes is permanently inactivated in somatic cells (cells other than egg cells). This process, known as X-inactivation, ensures that both females and males have only one active copy of the X chromosome in each body cell. As a result, in each somatic cell, the X chromosome that contains the focal dermal hypoplasia mutation may be turned on or turned off. Usually, X-inactivation occurs randomly. When X-inactivation does not occur randomly, it is called skewed X-inactivation. Researchers suspect that the distribution of active and inactive X chromosomes may play a role in determining the severity of focal dermal hypoplasia. As X-inactivation occurs in somatic cells, it does not affect the inheritance of a condition.
Last updated on 05-01-20
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