MedGen

A type of ataxia characterized by the impairment of the ability to smoothly perform the elements of a voluntary movement in the appropriate order and speed. With dyssynergia, a voluntary movement appears broken down into its component parts. [from HPO]

About half of all people with trichothiodystrophy have a photosensitive form of the disorder, which causes them to be extremely sensitive to ultraviolet (UV) rays from sunlight. They develop a severe sunburn after spending just a few minutes in the sun. However, for reasons that are unclear, they do not develop other sun-related problems such as excessive freckling of the skin or an increased risk of skin cancer. Many people with trichothiodystrophy report that they do not sweat.

Intellectual disability and delayed development are common in people with trichothiodystrophy, although most affected individuals are highly social with an outgoing and engaging personality. Some people with trichothiodystrophy have brain abnormalities that can be seen with imaging tests. A common neurological feature of this disorder is impaired myelin production (dysmyelination). Myelin is a fatty substance that insulates nerve cells and promotes the rapid transmission of nerve impulses.

Mothers of children with trichothiodystrophy may experience problems during pregnancy including pregnancy-induced high blood pressure (preeclampsia) and a related condition called HELLP syndrome that can damage the liver. Babies with trichothiodystrophy are at increased risk of premature birth, low birth weight, and slow growth. Most children with trichothiodystrophy have short stature compared to others their age. 

Trichothiodystrophy is also associated with recurrent infections, particularly respiratory infections, which can be life-threatening. People with trichothiodystrophy may have abnormal red blood cells, including red blood cells that are smaller than normal. They may also have elevated levels of a type of hemoglobin called A2, which is a protein found in red blood cells. Other features of trichothiodystrophy can include dry, scaly skin (ichthyosis); abnormalities of the fingernails and toenails; clouding of the lens in both eyes from birth (congenital cataracts); poor coordination; and skeletal abnormalities including degeneration of both hips at an early age.

The signs and symptoms of trichothiodystrophy vary widely. Mild cases may involve only the hair. More severe cases also cause delayed development, significant intellectual disability, and recurrent infections; severely affected individuals may survive only into infancy or early childhood.

In people with trichothiodystrophy, tests show that the hair is lacking sulfur-containing proteins that normally gives hair its strength. A cross section of a cut hair shows alternating light and dark banding that has been described as a "tiger tail."

Trichothiodystrophy, commonly called TTD, is a rare inherited condition that affects many parts of the body. The hallmark of this condition is hair that is sparse and easily broken.  [from MedlinePlus Genetics]

Ewing sarcoma is a cancerous tumor that occurs in bones or soft tissues, such as cartilage or nerves. There are several types of Ewing sarcoma, including Ewing sarcoma of bone, extraosseous Ewing sarcoma, peripheral primitive neuroectodermal tumor (pPNET), and Askin tumor. These tumors are considered to be related because they have similar genetic causes. These types of Ewing sarcoma can be distinguished from one another by the tissue in which the tumor develops. Approximately 87 percent of Ewing sarcomas are Ewing sarcoma of bone, which is a bone tumor that usually occurs in the thigh bones (femurs), pelvis, ribs, or shoulder blades. Extraosseous (or extraskeletal) Ewing sarcoma describes tumors in the soft tissues around bones, such as cartilage. pPNETs occur in nerve tissue and can be found in many parts of the body. A type of pPNET found in the chest is called Askin tumor.

Ewing sarcomas most often occur in children and young adults. Affected individuals usually feel stiffness, pain, swelling, or tenderness of the bone or surrounding tissue. Sometimes, there is a lump near the surface of the skin that feels warm and soft to the touch. Often, children have a fever that does not go away. Ewing sarcoma of bone can cause weakening of the involved bone, and affected individuals may have a broken bone with no obvious cause.

It is common for Ewing sarcoma to spread to other parts of the body (metastasize), usually to the lungs, to other bones, or to the bone marrow. [from MedlinePlus Genetics]

Crigler-Najjar syndrome is a severe condition characterized by high levels of a toxic substance called bilirubin in the blood (hyperbilirubinemia). Bilirubin is produced when red blood cells are broken down. This substance is removed from the body only after it undergoes a chemical reaction in the liver, which converts the toxic form of bilirubin (called unconjugated bilirubin) to a nontoxic form called conjugated bilirubin. People with Crigler-Najjar syndrome have a buildup of unconjugated bilirubin in their blood (unconjugated hyperbilirubinemia).

Crigler-Najjar syndrome is divided into two types. Type 1 (CN1) is very severe, and affected individuals can die in childhood due to kernicterus, although with proper treatment, they may survive longer. Type 2 (CN2) is less severe. People with CN2 are less likely to develop kernicterus, and most affected individuals survive into adulthood.

Bilirubin has an orange-yellow tint, and hyperbilirubinemia causes yellowing of the skin and whites of the eyes (jaundice). In Crigler-Najjar syndrome, jaundice is apparent at birth or in infancy. Severe unconjugated hyperbilirubinemia can lead to a condition called kernicterus, which is a form of brain damage caused by the accumulation of unconjugated bilirubin in the brain and nerve tissues. Babies with kernicterus are often extremely tired (lethargic) and may have weak muscle tone (hypotonia). These babies may experience episodes of increased muscle tone (hypertonia) and arching of their backs. Kernicterus can lead to other neurological problems, including involuntary writhing movements of the body (choreoathetosis), hearing problems, or intellectual disability. [from MedlinePlus Genetics]

Glucose phosphate isomerase (GPI) deficiency is an inherited disorder that affects red blood cells, which carry oxygen to the body's tissues. People with this disorder have a condition known as chronic hemolytic anemia, in which red blood cells are broken down (undergo hemolysis) prematurely, resulting in a shortage of red blood cells (anemia). Chronic hemolytic anemia can lead to unusually pale skin (pallor), yellowing of the eyes and skin (jaundice), extreme tiredness (fatigue), shortness of breath (dyspnea), and a rapid heart rate (tachycardia). An enlarged spleen (splenomegaly), an excess of iron in the blood, and small pebble-like deposits in the gallbladder or bile ducts (gallstones) may also occur in this disorder.

Hemolytic anemia in GPI deficiency can range from mild to severe. In the most severe cases, affected individuals do not survive to birth. Individuals with milder disease can survive into adulthood. People with any level of severity of the disorder can have episodes of more severe hemolysis, called hemolytic crises, which can be triggered by bacterial or viral infections.

A small percentage of individuals with GPI deficiency also have neurological problems, including intellectual disability and difficulty with coordinating movements (ataxia). [from MedlinePlus Genetics]

Complete LCAT deficiency is a disorder that primarily affects the eyes and kidneys.

In complete LCAT deficiency, the clear front surface of the eyes (the corneas) gradually becomes cloudy. The cloudiness, which generally first appears in early childhood, consists of small grayish dots of cholesterol (opacities) distributed across the corneas. Cholesterol is a waxy, fat-like substance that is produced in the body and obtained from foods that come from animals; it aids in many functions of the body but can become harmful in excessive amounts. As complete LCAT deficiency progresses, the corneal cloudiness worsens and can lead to severely impaired vision.

People with complete LCAT deficiency often have kidney disease that begins in adolescence or early adulthood. The kidney problems get worse over time and may eventually lead to kidney failure. Individuals with this disorder also usually have a condition known as hemolytic anemia, in which red blood cells are broken down (undergo hemolysis) prematurely, resulting in a shortage of red blood cells (anemia). Anemia can cause pale skin, weakness, fatigue, and more serious complications.

Other features of complete LCAT deficiency that occur in some affected individuals include enlargement of the liver (hepatomegaly), spleen (splenomegaly), or lymph nodes (lymphadenopathy) or an accumulation of fatty deposits on the artery walls (atherosclerosis). [from MedlinePlus Genetics]

Isobutyryl-CoA dehydrogenase (IBD) deficiency is a condition that disrupts the breakdown of certain proteins. Normally, proteins from food are broken down into parts called amino acids. Amino acids can be further processed to provide energy for growth and development. People with IBD deficiency have inadequate levels of an enzyme that helps break down a particular amino acid called valine.

Most people with IBD deficiency are asymptomatic, which means they do not have any signs or symptoms of the condition. A few children with IBD deficiency have developed features such as a weakened and enlarged heart (dilated cardiomyopathy), weak muscle tone (hypotonia), and developmental delay. This condition may also cause low numbers of red blood cells (anemia) and very low blood levels of carnitine, which is a natural substance that helps convert certain foods into energy. The range of signs and symptoms associated with IBD deficiency remains unclear because very few affected individuals have been reported. [from MedlinePlus Genetics]

Hypermethioninemia can occur with other metabolic disorders, such as homocystinuria, tyrosinemia, and galactosemia, which also involve the faulty breakdown of particular molecules. It can also result from liver disease or excessive dietary intake of methionine from consuming large amounts of protein or a methionine-enriched infant formula. The condition is called primary hypermethioninemia when it is not associated with other metabolic disorders or excess methionine in the diet.

People with hypermethioninemia often do not show any symptoms. Some individuals with hypermethioninemia exhibit intellectual disability and other neurological problems; delays in motor skills such as standing or walking; sluggishness; muscle weakness; liver problems; unusual facial features; and their breath, sweat, or urine may have a smell resembling boiled cabbage.

Hypermethioninemia is an excess of a particular protein building block (amino acid), called methionine, in the blood. This condition can occur when methionine is not broken down (metabolized) properly in the body. [from MedlinePlus Genetics]

Eliglustat is a glucosylceramide synthase inhibitor used in the treatment of Gaucher disease (GD). Eliglustat is indicated for the long-term treatment of adult individuals with Gaucher disease type 1 (GD1) who are CYP2D6 normal metabolizers, intermediate metabolizers, or poor metabolizers as detected by an FDA-cleared test. Gaucher disease is an autosomal recessive metabolic disorder characterized by accumulation of glucosylceramide (a sphingolipid also known as glucocerebroside) within lysosomes. This is caused by a malfunction of the enzyme acid beta-glucosidase, encoded by the gene GBA. Type 1 GD may present in childhood or adulthood with symptoms including bone disease, hepatosplenomegaly, thrombocytopenia, anemia and lung disease and –– unlike Gaucher types 2 and 3 –– does not directly affect the central nervous system primarily. Eliglustat, a ceramide mimic, inhibits the enzyme that synthesizes glucosylceramides (UDP-Glucose Ceramide Glucosyltransferase), thereby reducing the accumulation of these lipids in the lysosome. Eliglustat is broken down to inactive metabolites by CYP2D6 and, to a lesser extent, CYP3A. The dosage of eliglustat is based on the individual’s CYP2D6 metabolizer status. Individuals with normal CYP2D6 activity are termed normal metabolizers (NM), those with reduced activity are termed intermediate metabolizers (IM), and if activity is absent, poor metabolizers (PM). The FDA-approved drug label for eliglustat provides specific dosage guidelines based on their CYP2D6 status and concomitant usage of CYP2D6 or CYP3A inhibitors, and states that hepatic and renal function should also be considered when determining the appropriate dosage. The label also states that CYP2D6 ultrarapid metabolizers (UM) may not achieve adequate concentrations of eliglustat for a therapeutic effect, and that for individuals for whom a CYP2D6 genotype cannot be determined, a specific dosage cannot be recommended. Dosing recommendations for eliglustat have also been published by the Dutch Pharmacogenetics Working Group (DPWG) based on CYP2D6 metabolizer type and include dose adjustments for dosing eliglustat with medications that alter CYP2D6 and or CYP3A function. [from Medical Genetics Summaries]

Hyperprolinemia type II results in proline levels in the blood between 10 and 15 times higher than normal, and high levels of a related compound called pyrroline-5-carboxylate. This form of the disorder is more likely than type I to involve seizures or intellectual disability that vary in severity.

People with hyperprolinemia type I often do not show any symptoms, although they have proline levels in their blood between 3 and 10 times the normal level. Some individuals with hyperprolinemia type I exhibit seizures, intellectual disability, or other neurological or psychiatric problems.

Hyperprolinemia can also occur with other conditions, such as malnutrition or liver disease. In particular, individuals with conditions that cause elevated levels of a chemical called lactic acid in the blood (lactic acidosis) may have hyperprolinemia as well, because lactic acid stops (inhibits) the breakdown of proline.

Hyperprolinemia is an excess of a particular protein building block (amino acid), called proline, in the blood. This condition generally occurs when proline is not broken down properly by the body. There are two forms of hyperprolinemia, called type I and type II. [from MedlinePlus Genetics]

Some researchers believe that dentinogenesis imperfecta type II and type III, along with a condition called dentin dysplasia type II, are actually forms of a single disorder. The signs and symptoms of dentin dysplasia type II are very similar to those of dentinogenesis imperfecta. However, dentin dysplasia type II affects the primary teeth much more than the permanent teeth.

Researchers have described three types of dentinogenesis imperfecta with similar dental abnormalities. Type I occurs in people who have osteogenesis imperfecta, a genetic condition in which bones are brittle and easily broken. Dentinogenesis imperfecta type II and type III usually occur in people without other inherited disorders. A few older individuals with type II have had progressive high-frequency hearing loss in addition to dental abnormalities, but it is not known whether this hearing loss is related to dentinogenesis imperfecta.

Dentinogenesis imperfecta is a disorder of tooth development. This condition causes the teeth to be discolored (most often a blue-gray or yellow-brown color) and translucent. Teeth are also weaker than normal, making them prone to rapid wear, breakage, and loss. These problems can affect both primary (baby) teeth and permanent teeth. [from MedlinePlus Genetics]

Pegloticase is used to treat the high levels of uric acid associated with refractory gout. The use of pegloticase is reserved for individuals with symptomatic, chronic gout who have not responded to, or are unable to take, conventional gout treatments. Pegloticase is given once every 2 weeks as an intravenous infusion, and is given in a healthcare setting that is prepared to manage infusion reactions and anaphylaxis. Pegloticase is a pegylated urate oxidase – a modified version of the enzyme that catalyzes the oxidation of uric acid to 5-hydroxyisourate and hydrogen peroxide in most mammalian species. However, urate oxidase is not active in humans due to an inactivating mutation in the gene. Subsequent hydrolysis and decarboxylation of 5-hydroxyisourate leads to the formation of a more soluble metabolite (allantoin), which is then excreted by the kidneys. Red blood cells that lack the glucose-6-phosphate dehydrogenase (G6PD) enzyme are sensitive to oxidative damage caused by agents like hydrogen peroxide. Once exposed, the red blood cells become rigid, trapped, and are rapidly broken down (hemolysis). This can lead to a deficiency of mature red blood cells (hemolytic anemia) and the production of red blood cells with abnormally high levels of methemoglobin (methemoglobinemia). Approximately 400 million people worldwide have G6PD deficiency. Most of these individuals are asymptomatic. However, they are at risk of life-threating hemolytic reactions and methemoglobinemia if given oxidizing drugs such as pegloticase. Pegloticase is contraindicated in individuals with G6PD deficiency. The FDA-approved label states that individuals at higher risk for G6PD deficiency should be screened before starting pegloticase therapy, with specific examples including individuals of African, Mediterranean (including Southern European and Middle Eastern), and South Asian ancestry. Importantly, approximately 12% of African-Americans have G6PD deficiency. [from Medical Genetics Summaries]

Chromosome 16p13.3deletion syndrome is a chromosome abnormality that can affect many parts of the body. People with this condition are missing a small piece (deletion) of chromosome 16 at a location designated p13.3. Although once thought to be a severe form of Rubinstein-Taybi syndrome, it is now emerging as a unique syndrome. Signs and symptoms may include failure to thrive, hypotonia (reduced muscle tone), short stature, microcephaly (unusually small head), characteristic facial features, mild to moderate intellectual disability, organ anomalies (i.e. heart and/or kidney problems), and vulnerability to infections. Chromosome testing of both parents can provide information about whether the deletion was inherited. In most cases, parents do not have any chromosome abnormalities. However, sometimes one parent has a balanced translocation where a piece of a chromosome has broken off and attached to another one with no gain or loss of genetic material. The balanced translocation normally does not cause signs or symptoms, but it increases the risk for having a child with a chromosome abnormality like a deletion. Treatment is based on the signs and symptoms present in each person.To learn more about chromosome abnormalities in general, view our GARD fact sheet on Chromosome Disorders. [from MONDO]

Autosomal recessive hypotrichosis is a condition that affects hair growth. People with this condition have sparse hair (hypotrichosis) on the scalp beginning in infancy. This hair is usually coarse, dry, and tightly curled (often described as woolly hair). Scalp hair may also be lighter in color than expected and is fragile and easily broken. Affected individuals often cannot grow hair longer than a few inches. The eyebrows, eyelashes, and other body hair may be sparse as well. Over time, the hair problems can remain stable or progress to complete scalp hair loss (alopecia) and a decrease in body hair.

Rarely, people with autosomal recessive hypotrichosis have skin problems affecting areas with sparse hair, such as redness (erythema), itchiness (pruritus), or missing patches of skin (erosions) on the scalp. In areas of poor hair growth, they may also develop bumps called hyperkeratotic follicular papules that develop around hair follicles, which are specialized structures in the skin where hair growth occurs. [from MedlinePlus Genetics]

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired (not inherited) disorder that leads to the premature death and impaired production of blood cells. The disorder affects red blood cells (erythrocytes), which carry oxygen; white blood cells (leukocytes), which protect the body from infections; and platelets (thrombocytes), which are involved in blood clotting. PNH can occur at any age, although it is most often diagnosed in young adulthood.

People with PNH have sudden, recurring episodes of symptoms (paroxysmal symptoms), which may be triggered by stresses on the body, such as infections or physical exertion. During these episodes, red blood cells are broken down earlier than they should be (hemolysis). Affected individuals may pass dark-colored urine because of the presence of hemoglobin, the oxygen-carrying protein in blood. The abnormal presence of hemoglobin in the urine is called hemoglobinuria. In many, but not all cases, hemoglobinuria is most noticeable early in the morning, upon passing urine that has accumulated in the bladder during the night (nocturnal).

The premature breakdown of red blood cells results in a shortage of these cells in the blood (hemolytic anemia), which can cause signs and symptoms such as fatigue, weakness, abnormally pale skin (pallor), shortness of breath, and an increased heart rate (tachycardia). People with PNH may also be prone to infections because of a shortage of white blood cells (leukopenia).

Abnormal platelets associated with PNH can cause problems in the blood clotting process. As a result, people with this disorder may experience abnormal blood clotting (thrombosis), especially in large abdominal veins; or, less often, episodes of severe bleeding (hemorrhage).

Individuals with PNH are at increased risk of developing cancer in blood-forming cells (leukemia). In some cases, people who have or have been treated for another blood disease called aplastic anemia may develop PNH. In a small number of affected individuals, the signs and symptoms of PNH disappear on their own.

A very rare form of PNH involves abnormal inflammation in addition to the typical features described above. Inflammation is a normal immune system response to injury and foreign invaders (such as bacteria). In people with this rare form of PNH, the immune response is turned on (activated) abnormally and can cause recurrent aseptic meningitis (which is inflammation of the membranes surrounding the brain and spinal cord that is not related to infection); a red, itchy rash (known as hives or urticaria); joint pain (arthralgia); or inflammatory bowel disease. The inflammatory disorders usually begin earlier than the blood cell problems. [from MedlinePlus Genetics]

Syndrome with the association of stubby, coarse, sparse and fragile hair, eyebrows and eyelashes with photosensitivity and nonprogressive intellectual deficit, without a demonstrable metabolic aberration. It has been described in three sisters born to consanguineous parents. [from SNOMEDCT_US]

Paget disease of bone is a disorder that causes bones to grow larger and weaker than normal. Affected bones may be misshapen and easily broken (fractured).

Early-onset Paget disease of bone is a less common form of the disease that appears in a person's teens or twenties. Its features are similar to those of the classic form of the disease, although it is more likely to affect the skull, spine, and ribs (the axial skeleton) and the small bones of the hands. The early-onset form of the disorder is also associated with hearing loss early in life.

The classic form of Paget disease of bone typically appears in middle age or later. It usually occurs in one or a few bones and does not spread from one bone to another. Any bones can be affected, although the disease most commonly affects bones in the spine, pelvis, skull, or legs.

Many people with classic Paget disease of bone do not experience any symptoms associated with their bone abnormalities. The disease is often diagnosed unexpectedly by x-rays or laboratory tests done for other reasons. People who develop symptoms are most likely to experience pain. The affected bones may themselves be painful, or pain may be caused by arthritis in nearby joints. Arthritis results when the distortion of bones, particularly weight-bearing bones in the legs, causes extra wear and tear on the joints. Arthritis most frequently affects the knees and hips in people with this disease.

Other complications of Paget disease of bone depend on which bones are affected. If the disease occurs in bones of the skull, it can cause an enlarged head, hearing loss, headaches, and dizziness. If the disease affects bones in the spine, it can lead to numbness and tingling (due to pinched nerves) and abnormal spinal curvature. In the leg bones, the disease can cause bowed legs and difficulty walking.

A rare type of bone cancer called osteosarcoma has been associated with Paget disease of bone. This type of cancer probably occurs in less than 1 in 1,000 people with this disease. [from MedlinePlus Genetics]

About half of all people with trichothiodystrophy have a photosensitive form of the disorder, which causes them to be extremely sensitive to ultraviolet (UV) rays from sunlight. They develop a severe sunburn after spending just a few minutes in the sun. However, for reasons that are unclear, they do not develop other sun-related problems such as excessive freckling of the skin or an increased risk of skin cancer. Many people with trichothiodystrophy report that they do not sweat.

Trichothiodystrophy is also associated with recurrent infections, particularly respiratory infections, which can be life-threatening. People with trichothiodystrophy may have abnormal red blood cells, including red blood cells that are smaller than normal. They may also have elevated levels of a type of hemoglobin called A2, which is a protein found in red blood cells. Other features of trichothiodystrophy can include dry, scaly skin (ichthyosis); abnormalities of the fingernails and toenails; clouding of the lens in both eyes from birth (congenital cataracts); poor coordination; and skeletal abnormalities including degeneration of both hips at an early age.

Intellectual disability and delayed development are common in people with trichothiodystrophy, although most affected individuals are highly social with an outgoing and engaging personality. Some people with trichothiodystrophy have brain abnormalities that can be seen with imaging tests. A common neurological feature of this disorder is impaired myelin production (dysmyelination). Myelin is a fatty substance that insulates nerve cells and promotes the rapid transmission of nerve impulses.

Mothers of children with trichothiodystrophy may experience problems during pregnancy including pregnancy-induced high blood pressure (preeclampsia) and a related condition called HELLP syndrome that can damage the liver. Babies with trichothiodystrophy are at increased risk of premature birth, low birth weight, and slow growth. Most children with trichothiodystrophy have short stature compared to others their age. 

The signs and symptoms of trichothiodystrophy vary widely. Mild cases may involve only the hair. More severe cases also cause delayed development, significant intellectual disability, and recurrent infections; severely affected individuals may survive only into infancy or early childhood.

In people with trichothiodystrophy, tests show that the hair is lacking sulfur-containing proteins that normally gives hair its strength. A cross section of a cut hair shows alternating light and dark banding that has been described as a "tiger tail."

Trichothiodystrophy, commonly called TTD, is a rare inherited condition that affects many parts of the body. The hallmark of this condition is hair that is sparse and easily broken.  [from MedlinePlus Genetics]

Autosomal recessive hypotrichosis is a condition that affects hair growth. People with this condition have sparse hair (hypotrichosis) on the scalp beginning in infancy. This hair is usually coarse, dry, and tightly curled (often described as woolly hair). Scalp hair may also be lighter in color than expected and is fragile and easily broken. Affected individuals often cannot grow hair longer than a few inches. The eyebrows, eyelashes, and other body hair may be sparse as well. Over time, the hair problems can remain stable or progress to complete scalp hair loss (alopecia) and a decrease in body hair.

Rarely, people with autosomal recessive hypotrichosis have skin problems affecting areas with sparse hair, such as redness (erythema), itchiness (pruritus), or missing patches of skin (erosions) on the scalp. In areas of poor hair growth, they may also develop bumps called hyperkeratotic follicular papules that develop around hair follicles, which are specialized structures in the skin where hair growth occurs. [from MedlinePlus Genetics]

Marsili syndrome (MARSIS) is an autosomal dominant pain insensitivity disorder characterized by a lowered ability to sense pain, to experience temperature, and to sweat. Affected individuals do not perceive broken bones and burns as painful, and have lowered sensitivity to capsaicin. However, visceral pain (e.g., childbirth-related) and light touch are perceived (summary by Habib et al., 2018). [from OMIM]