Horizon Screening Options

Comprehensive
screening options

Comprehensive
screening options

Comprehensive
screening options

Comprehensive
screening options

Disease List:

3 6 A B C D E F G H I J K L M N O P R S T U V W Z

Bilateral Frontoparietal Polymicrogyria

  • Horizon 274

What is Bilateral Frontoparietal Polymicrogyria?

Bilateral Frontoparietal Polymicrogyria is an autosomal recessive disorder that causes abnormal development of the brain that starts before birth. The outer surface of the brain normally has ridges or folds, called gyri. In people with polymicrogyria, the brain develops too many folds that are too small in size. Bilateral Frontoparietal Polymicrogyria affects the frontal and parietal lobes on both sides of the brain. Signs and symptoms typically include developmental delay, moderate to severe intellectual disability, seizures, problems with muscle coordination, trouble with speech and swallowing, and eye problems including crossed eyes. There is no cure for this disorder and treatment is based on the symptoms.

What causes Bilateral Frontoparietal Polymicrogyria?

Bilateral Frontoparietal Polymicrogyria is caused by a gene change, or mutation, in both copies of the GPR56 gene pair.  These mutations cause the genes to not work properly or not work at all.  When both copies of this gene do not work correctly, it leads to the symptoms described above. 

Biotinidase Deficiency

  • Horizon 137
  • Horizon 274

What is Biotinidase Deficiency?

Biotinidase Deficiency is an autosomal recessive disorder in which the body is unable to reuse a B vitamin called biotin.  This condition is treatable in affected infants and children by giving biotin.  If this condition is not identified in infancy and treated, signs and symptoms typically appear in the first few months of life but can sometimes begin later in childhood.

If untreated, Biotinidase Deficiency can cause delayed development, seizures, weak muscle tone (hypotonia), breathing problems, hearing and vision loss, problems with movement and balance, skin rashes, hair loss, and yeast infections.  Some children have a milder form of this condition, and some never develop symptoms.  Lifelong treatment with biotin supplements can prevent these complications from occurring. With early diagnosis and treatment with biotin, people with Biotinidase Deficiency can live healthy lives with no symptoms.

What causes Biotinidase Deficiency?

Biotinidase Deficiency is caused by a gene change, or mutation, in both copies of the BTD gene pair.  These mutations cause the genes to not work properly or not work at all.  When both copies of the BTD gene do not work correctly, it leads to the symptoms described above

Bloom Syndrome

  • Horizon 27
  • Horizon 106
  • Horizon 137
  • Horizon 274

What is Bloom Syndrome?

Bloom Syndrome is an autosomal recessive disorder that causes growth delay, sensitivity to sunlight, immune system problems, increased risk for cancer, and sometimes intellectual disability. Most people with Bloom Syndrome live into adulthood but lifespan may be decreased.  Currently there is no cure for this condition and treatment is based on symptoms.

What causes Bloom Syndrome?

Bloom Syndrome is caused by a gene change, or mutation, in both copies of the BLM gene pair.  These mutations cause the genes to not work properly or not work at all. When both copies of the BLM gene do not work correctly, it causes instability in the chromosomes (structures that contain genes), which leads to the health problems listed above.  

Canavan Disease

  • Horizon 27
  • Horizon 106
  • Horizon 137
  • Horizon 274

What is Canavan Disease?

Canavan Disease is an autosomal recessive disorder that causes abnormal muscle tone, developmental delay, and progressive intellectual disability. Hearing and vision loss may also occur.  Lifespan is decreased. Some children with Canavan Disease only live into early childhood while others will survive into their teens.  In rare cases, symptoms are less severe and typically include motor and speech delays and mild intellectual disability. Currently there is no cure or specific treatment for this condition.

What causes Canavan Disease?

Canavan Disease is caused by a gene change, or mutation, in both copies of the ASPA gene pair.  These mutations cause the genes to not work properly or not work at all.  When both copies of the ASPA gene do not work correctly, it leads to the symptoms described above. 

Carbamoyl Phosphate Synthetase I Deficiency

  • Horizon 274

What is Carbamoyl Phosphate Synthetase I Deficiency?

Carbamoyl Phosphate Synthetase I Deficiency (CPS) is an autosomal recessive disorder that causes a buildup of ammonia in the blood.  High ammonia levels can cause damage to the brain and nervous system. Signs and symptoms of the most common early-onset form often begin shortly after birth.  Symptoms may include sleepiness, poor appetite, breathing problems, vomiting, seizures, and unusual body movements.  If left untreated, some children have delayed development and intellectual disability.  Symptoms may occur after eating food high in protein, or during illness and can be life-threatening. Some people with this condition have a delayed-onset form that causes milder symptoms beginning later in life.  Children with this condition who have ongoing medical treatment and follow a special low-protein diet may be able to avoid some of the effects of this disorder. However, even with careful treatment, some children still have repeated episodes high blood ammonia.   

What causes Carbamoyl Phosphate Synthetase I Deficiency?

Carbamoyl Phosphate Synthetase I Deficiency is caused by a gene change, or mutation, in both copies of the CPS1 gene pair. These mutations cause the genes to not work properly or not work at all.  When both copies of the CPS1 gene do not work correctly, it leads to the symptoms described above.

Carnitine Deficiency

  • Horizon 137
  • Horizon 274

What is Carnitine Deficiency?

Carnitine Deficiency (also called Carnitine Uptake Defect, Primary Carnitine Deficiency, or Carnitine Transporter Deficiency) is an autosomal recessive disorder in which certain fats cannot be broken down and used for energy because the body cannot process carnitine. Carnitine is a substance that is found in food and helps the body turn fat into energy. Signs and symptoms of Carnitine Deficiency may begin shortly after birth or in childhood.  People with this condition may have low blood sugar (hypoglycemia), lack of energy, poor appetite, breathing problems, vomiting, diarrhea, low blood sugar, and confusion.  Symptoms often appear during an illness or after going a long time without food, and can be life-threatening if not treated.  Children with this disorder who do not receive treatment may develop an enlarged heart, muscle weakness, and liver disease.  Some people with Carnitine Deficiency never have symptoms of this condition. Treatment with carnitine can help prevent or reverse the signs and symptoms of Carnitine Deficiency. Children with this disorder who receive treatment can have healthy growth and development.

What causes Carnitine Deficiency?

Carnitine Deficiency is caused by a gene change, or mutation, in both copies of the SLC22A5 gene pair.  These mutations cause the genes to not work properly or not work at all.  When both copies of the SLC22A5 gene do not work correctly, it leads to the symptoms described above.

Carnitine Palmitoyltransferase IA Deficiency

  • Horizon 137
  • Horizon 274

What is Carnitine Palmitoyltransferase IA Deficiency?

Carnitine Palmitoyltransferase IA (CPT1A) Deficiency is an autosomal recessive disorder in which the body is unable to break down certain fats for energy.  Symptoms of Carnitine Palmitoyltransferase IA Deficiency usually begin in infancy.  Children with Carnitine Palmitoyltransferase IA Deficiency can have lethargy (extreme tiredness), irritability, appetite problems, vomiting, diarrhea, low blood sugar (hypoglycemia), seizures, and breathing problems.  Symptoms may appear after going a long time without eating or with illness and can be life-threatening.  Enlarged liver and muscle weakness sometimes also occur. Some children have milder symptoms and fewer health problems. Occasionally, the symptoms do not begin until adulthood and include just muscle cramping, pain, and weakness during exercise without the other symptoms. Lifelong dietary and medical treatment can help prevent or lessen the symptoms of Carnitine Palmitoyltransferase IA Deficiency.  With early diagnosis and careful treatment, children with Carnitine Palmitoyltransferase IA Deficiency often have healthy growth and development.

What causes Carnitine Palmitoyltransferase IA Deficiency?

Carnitine Palmitoyltransferase IA Deficiency is caused by a change, or mutation, in both copies of the CPT1A gene pair.  These mutations cause the genes to not work properly or not work at all. The CPT1A genes help the body break down a certain type of fat and change it into energy. When both copies of this gene do not work correctly, it can cause low blood sugar and the buildup of this fat in the liver, heart, and brain, leading to the symptoms described above. 

Carnitine Palmitoyltransferase II Deficiency

  • Horizon 106
  • Horizon 137
  • Horizon 274

What is Carnitine Palmitoyltransferase II Deficiency?

Carnitine Palmitoyltransferase II (CPT II) Deficiency is an autosomal recessive disorder in which the body is unable to breakdown certain fats for energy.  Signs and symptoms of Carnitine Palmitoyltransferase II Deficiency begin in infancy, childhood, or in adulthood.   Infants with the severe form can have abnormal development of the brain and kidneys, and life-threatening problems including breathing problems, low blood sugar (hypoglycemia), seizures, liver disease, and heart disease.  Affected children can have poor muscle tone (hypotonia), extreme tiredness, irritability, feeding problems, fever, diarrhea, vomiting and low blood sugar (hypoglycemia).  Other problems can include developmental delays, heart disease, liver disease, and seizures.  Symptoms may appear after going a long time without food or with illness and can be life-threatening.  Some affected individuals have a form that affects the muscles only, causing muscle pain and weakness. 

Lifelong dietary and medical treatment can help prevent some of the signs and symptoms of Carnitine Palmitoyltransferase II Deficiency.  With early diagnosis and careful treatment individuals with Carnitine Palmitoyltransferase II Deficiency can have healthy growth and development.

What causes Carnitine Palmitoyltransferase II Deficiency?

Carnitine Palmitoyltransferase II Deficiency is caused by a change, or mutation, in both copies of the CPT2 gene.  These mutations cause the genes to not work properly or not work at all.  The job of the CPT2 genes is to help the body breakdown a certain type of fat and change it into energy. When both copies of this gene do not work correctly, it can cause low blood sugar and the buildup of this fat in the liver, heart, and brain which leads to the symptoms described above.

Carpenter Syndrome

  • Horizon 274

What is Carpenter Syndrome?

Carpenter Syndrome is an inherited disorder that causes defects of the skull bones, hands, and feet as well as other parts of the body.  Children with Carpenter Syndrome are born with craniosynostosis (fused skull bones) which affects the shape of the head and the appearance of the face.  This can cause increased pressure in the skull and abnormal brain development if not corrected by surgery.  Children with Carpenter Syndrome often have shortened fingers and toes with webbing of the skin between them (syndactyly).  Some people with Carpenter Syndrome have mild to severe intellectual disability.  Other health problems happen sometimes and may include additional bone abnormalities, heart defects, vision and hearing problems, oral and dental abnormalities, obesity, and or genital abnormalities.  The signs and symptoms of Carpenter Syndrome vary among affected people.  

What causes Carpenter Syndrome?

Carpenter Syndrome is caused by a change, or mutation, in both copies of the RAB23 gene.  These mutations cause the genes to not work properly or not work at all.  When both copies of this gene pair do not work correctly, it causes the health problems described above.

Cartilage-Hair Hypoplasia

  • Horizon 137
  • Horizon 274

What is Cartilage-Hair Hypoplasia?

Cartilage-Hair Hypoplasia (also known as Metaphyseal Dysplasia, Type McKusick) is an autosomal recessive disorder that affects the hair, bones, and the digestive and immune systems.  Signs and symptoms include abnormally fine, sparse, brittle, light-colored hair; bone abnormalities that lead to short stature due to short arms and legs (short-limbed dwarfism); constipation; problems digesting some nutrients and gluten from food; repeated infections; and increased risk for certain cancers (basal cell, leukemia, and lymphoma). The immune system impairment varies from mild to severe. People with the most severe immune system problems have repeated and long-lasting infections that can be life-threatening. Some people also have other symptoms that may include light-colored skin and abnormalities of the nails and teeth. 

Rarely, mutations in the same gene cause a related disorder, either Metaphyseal Dysplasia without Hypotrichosis or Anauxetic Dysplasia.  Metaphyseal Dysplasia without Hypotrichosis has similar bone symptoms and short stature as Cartilage-Hair Hypoplasia but does not cause hair abnormalities, immune system or digestive problems, or anemia.  Anauxetic Dysplasia causes more severe bone abnormalities and very short stature, distinct facial features, abnormalities of the teeth, and mild intellectual disability.  It is sometimes, but not always, possible to determine which of these disorders a specific mutation in the RMPR gene will cause.  Currently there is no cure for any of these conditions and treatment is based on the symptoms.

What causes Cartilage-Hair Hypoplasia?

Cartilage-Hair Hypoplasia is caused by a gene change, or mutation, in both copies of the RMRP gene pair.  These mutations cause the genes to not work properly or not work at all.   When both copies of this gene do not work correctly, it leads to the symptoms described above. 

Cerebrotendinous Xanthomatosis

  • Horizon 106
  • Horizon 137
  • Horizon 274

What is Cerebrotendinous Xanthomatosis?

Cerebrotendinous Xanthomatosis is an autosomal recessive lipid (fat) storage disorder.  People with this condition have difficulty breaking down different forms of cholesterol, causing these and other fats to build up in various parts of the body in the form of xanthomas.  Xanthomas are yellow, fatty nodules which are most often found in the brain and tendons of people with Cerebrotendinous Xanthomatosis.  It is important to treat this condition as symptoms can worsen over time due to the accumulation of excess fats throughout tissues in the body, although increased cholesterol levels are not found in the blood.  The number and severity of symptoms will vary from person to person so no two people with Cerebrotendinous Xanthomatosis will be affected the same, even within the same family.

Features of Cerebrotendinous Xanthomatosis can include chronic diarrhea starting in infancy, clouding of the lens of the eye (cataracts) developing in late childhood, progressively brittle bones that are prone to break, and neurological problems in adulthood, such as dementia with decreasing intellectual abilities, seizures, hallucinations, depression, and difficulty with coordinating movements (ataxia) and speech (dysarthria).  The neurological symptoms that occur are thought to be related to the excess amounts of circulating fats and the xanthomas that develop in the brain.  Xanthomas that develop in tendons may cause discomfort and lessen tendon flexibility.  People with Cerebrotendinous Xanthomatosis also have an increased risk for heart disease. 

What causes Cerebrotendinous Xanthomatosis?

Cerebrotendinous Xanthomatosis is caused by a gene change, or mutation, in both copies of the CYP27A1 gene pair.  These mutations cause the genes to not work properly or not work at all.  When both copies of this gene do not work correctly, it leads to the symptoms described above.

Charcot-Marie-Tooth Disease with Deafness, X-linked

  • Horizon 274

Charcot-Marie-Tooth Disease with Deafness, X-Linked (also called CMTX1) is a condition that occurs mainly in boys and causes progressive nerve damage. This nerve damage leads to muscle weakness, poor coordination and balance, numbness or lack of feeling to touch and vibration, and decreased ability to feel pain or temperature changes. As the disease progresses, people with Charcot-Marie-Tooth Disease with Deafness, X-Linked can have problems with muscle weakness in the limbs, coordination, walking, and speech. Weakness of the feet and ankles and a foot deformity known as pes cavus (high arched foot) is common. Hearing loss occurs in some individuals. A small number of individuals need a wheelchair in adulthood. Symptoms typically begin between early childhood and adulthood and develop slowly over time. Intelligence and lifespan are normal. Female carriers may develop symptoms; however, they are typically milder than those seen in males.

 

What causes Charcot-Marie-Tooth Disease with Deafness, X-Linked?

Charcot-Marie-Tooth Disease with Deafness, X-Linked is caused by a change, or mutation, in the GJB1 gene.  When the GJB1 gene is not working properly it can lead to the symptoms described above.

CMTX1 is an X-linked condition, meaning it is caused by a mutation (change) in the GJB1 gene on the X chromosome. Females have two copies of the X chromosome, but males only have one copy. If a boy has a mutation in his GJB1 gene, he will be affected with CMTX1. A girl who has a mutation in the GJB1 gene on one of her X chromosomes is a carrier of CMTX1, and may or may not have some symptoms which, if present, are typically milder. CMTX1 is usually inherited from a mother who is a carrier of a mutation in the GJB1 gene.  

Charcot-Marie-Tooth Disease, Type 4D

  • Horizon 274

What is Charcot-Marie-Tooth Disease, Type 4D?

Charcot-Marie-Tooth Disease, Type 4D (CMT4D) is an autosomal recessive disorder that causes damage to the peripheral nerves (the nerves outside the brain and spinal cord).  Signs of the condition usually begin in childhood and worsen with age. Symptoms include deafness and loss of feeling and muscle wasting in the legs, hands, and feet. The hearing loss may begin in childhood but more commonly starts in adulthood. As the disease progresses, people with this condition often have problems with muscle weakness, coordination, walking, and speech. A high arched foot, known as pes cavus, is common. Some people need a wheelchair in adulthood.  CMT4D does not cause intellectual disability and lifespan is usually normal.  Currently there is no cure for CMT4D and treatment is based on symptoms.

What causes Charcot-Marie-Tooth Disease, Type 4D?

Charcot-Marie-Tooth Disease, Type 4D is caused by a gene change, or mutation, in both copies of the NDRG1 gene.  These mutations cause the genes to not work properly or not work at all.  When both copies of this gene do not work correctly, it causes the symptoms described above.

Choreoacanthocytosis

  • Horizon 106
  • Horizon 274

What is Choreoacanthocytosis?

Choreoacanthocytosis is an autosomal recessive disorder that causes neurological problems and abnormally shaped red blood cells.  People with this disorder have involuntary jerking movements (chorea) and muscle spasms (dystonia) that worsen over time. The chorea and dystonia occur mainly in the muscles of the limbs, face, mouth, tongue, and throat. Abnormal red blood cells shaped like stars (acanthocytosis) are also common. Seizures develop in about half of all people with this condition and changes in behavior and loss of memory often occur as the condition progresses. People with Choreoacanthocytosis usually start showing symptoms around the age of 30, although symptoms can start as early as age 10 or as late as age 70.  There is currently no cure for Choreoacanthocytosis and lifespan is reduced.

What causes Choreoacanthocytosis?

Choreoacanthocytosis is caused by a gene change, or mutation, in both copies of the VPS13A gene. These mutations cause the genes to not work properly or not work at all.  When both copies of this gene pair do not work correctly, it causes the symptoms described above.

Choroideremia

  • Horizon 274

What is Choroideremia?

Choroideremia is an X-linked inherited condition that causes progressive vision loss, mainly in boys and men. The first sign of Choroideremia is typically loss of night vision.  This can sometimes occur during childhood but usually begins in the teens.  Loss of peripheral vision (ability to see things on the side when looking straight ahead) follows night blindness and eventually leads to complete blindness in late adulthood.  

What causes Choroideremia?

Choroideremia is caused by a change, or mutation, in the CHM gene.  This mutation causes the gene to not work properly or not work at all.   When the CHM gene in a male is not working correctly, it leads to the symptoms described above. 

Chronic Granulomatous Disease, CYBA-Related

  • Horizon 106
  • Horizon 274

What is Chronic Granulomatous Disease, CYBA-Related?

Chronic Granulomatous Disease, CYBA-Related (also called Chronic Granulomatous Disease, Cytochrome b-negative) is an autosomal recessive disorder that affects the immune system and reduces the body’s ability to fight infection. The immune system is unable to kill bacteria, fungi, and yeast infections and, instead, the immune cells in the body form walls around the infections, forming ‘knots’ called granulomas and chronic inflammation. The lungs are the most common place for infections but they can also occur in the lymph nodes, liver, bladder, bone, skin, and intestines. Individuals with this condition are also at increased risk for autoimmune diseases. Symptoms can begin anytime between infancy to adulthood but most will have symptoms before the age of five. Long-term use of medication is often needed to treat infections and reduce inflammation. Bone marrow or stem cell transplantation is the only known cure for this condition but, due to the risks involved in this treatment, it may be considered for some but not all people with this condition.

 

What causes Chronic Granulomatous Disease, CYBA-Related?

Chronic Granulomatous Disease, CYBA-Related is caused by a gene change, or mutation, in both copies of the CYBA gene pair. These mutations cause the genes to not work properly or not work at all. When both copies of this gene do not work correctly, it leads to the symptoms described above.

Chronic Granulomatous Disease, X-Linked

  • Horizon 137
  • Horizon 274

What is Chronic Granulomatous Disease, X-Linked?

Chronic Granulomatous Disease, X-Linked is an X-linked inherited disorder that decreases the body’s ability to fight infection. The body is unable to kill bacteria and fungi which then cause infections and inflammation (swelling). The immune cells in the body form a wall around bacteria and infection, forming “knots” called granulomas. Repeated infections occur and often develop in the lungs, lymph nodes, liver, bones, skin, bladder, and gastrointestinal system. Diseases caused by inflammation, such as colitis, bladder and kidney problems happen even when there is no infection present. Symptoms can begin anytime between infancy to adulthood; however most will have symptoms before the age of five. Finding the type of infection and treating it immediately is very important.  Medications are often needed to treat infections. Usually males are affected with Chronic Granulomatous Disease, X-Linked and females are carriers and rarely have symptoms.

What causes Chronic Granulomatous Disease, X-Linked?

Chronic Granulomatous Disease, X-Linked is caused by a change, or mutation, in the CYBB gene.  The role of the CYBB gene is to make a protein that is important for immune system. When the CYBB gene is not working properly in a male it leads to the symptoms described above. 

Ciliopathies, RPGRIP1L-Related

  • Horizon 274

What is Ciliopathies, RPGRIP1L-Related?

Ciliopathies, RPGRIP1L-Related refers to a group of autosomal recessive disorders that cause abnormalities of the cilia, the hair-like structures on the outside of many body cells that help with sensing what’s happening around them and, in some areas of the body, helping move substances like mucus.  The group of Ciliopathies, RPGRIP1L-Related include the following disorders: Joubert Syndrome Type 7; Meckel Syndrome Type 5; COACH Syndrome; and Familial Aplasia of the Vermis.

Joubert Syndrome Type 7 has signs and symptoms that begin in infancy and affect the brain and kidneys and include abnormalities of the cerebellum of the brain, developmental delay, intellectual disability, ataxia (gait problems), poor muscle tone (hypotonia), breathing problems, abnormal eye movements, and kidney disease. Lifespan is often shortened.  Meckel Syndrome Type 5 causes multiple birth defects including encephalocele (protrusion of the brain through the skull), cleft lip and palate, cystic kidneys, and extra fingers and toes and other problems. Some infants are born with anencephaly, a severe lethal brain defect where parts of the brain and skull do not develop. Meckel Syndrome often leads to death in infancy.  Symptoms of COACH Syndrome are similar to Joubert Syndrome Type 7, but with liver disease called hepatic fibrosis.  Familial Aplasia of the Vermis causes abnormalities in the part of the brain called the cerebellar vermis which leads to ataxia with coordination and movement problems.  Currently there is no cure for these conditions and treatment is based on symptoms.

What causes Ciliopathies, RPGRIP1L-Related?

Ciliopathies, RPGRIP1L-Related are caused by a gene change, or mutation, in both copies of the RPGRIP1L gene pair.  These mutations cause the genes to not work properly or not work at all.  When both copies of this gene do not work correctly, it leads to the symptoms of one of the disorders described above. It is sometimes, but not always, possible to determine which specific disease in the group of Ciliopathies, RPGRIP1L-Related a specific mutation in the RPGRIP1L gene is likely to cause. 

Citrin Deficiency

  • Horizon 137
  • Horizon 274

What is Citrin Deficiency?

Citrin Deficiency, also known as Citrullinemia type II, is an autosomal recessive disorder with symptoms that begin either in infancy or later in adolescence or adulthood.  Affected infants can have jaundice (yellow skin and eyes), growth delay, liver disease, and hypoglycemia (low blood sugar). Symptoms may appear after going a long time without food or during illness. These symptoms often resolve by 6 to 12 months of age. However, some affected infants will have continued problems that may include liver cirrhosis and severe infections later in life. Adult-onset Citrin Deficiency symptoms include sudden onset of disorientation, abnormal behavior, seizures, liver disease, and coma due to high blood ammonia levels. Treatment often includes low carbohydrate diet and certain supplements. If the condition is not treated, liver transplant may be needed.

What causes Citrin Deficiency?

Citrin Deficiency is caused by a gene change, or mutation, in both copies of the SLC25A13 gene pair. These mutations cause the genes to not work properly or not work at all. The SLC25A13 genes provide instructions for making a protein called citrin, which is important in many parts of the body.  When both copies of this gene pair do not work correctly, it causes the symptoms described above. 

Citrullinemia, Type 1

  • Horizon 27
  • Horizon 106
  • Horizon 137
  • Horizon 274

What is Citrullinemia, Type 1?

Citrullinemia, Type 1 is an autosomal recessive disorder in which the body is unable to remove certain waste products, specifically ammonia, which leads to a toxic buildup in the body.  There are several types of Citrullinemia, Type 1.  In the severe form, life-threatening problems begin in the first days of life with lethargy, poor feeding, vomiting, seizures, and coma.  Some people have a later-onset (childhood or adulthood) type Citrullinemia, Type 1 with symptoms that include headaches, vision loss, problems with balance and muscle coordination (ataxia), and lethargy (extreme tiredness).  Some people with Citrullinemia, Type 1 never experience signs and symptoms of the disorder.  Treatment includes lifelong dietary and medical management. 

What causes Citrullinemia, Type 1?

Citrullinemia, Type 1 is caused by a gene change, or mutation, in both copies of the ASS1 gene pair.  These mutations cause the genes to not work properly or not work at all.  The function of the ASS1 genes is to breakdown specific toxins in the body.  When both copies of this gene do not work correctly, it causes buildup of toxins, including ammonia, which leads to the symptoms described above.

Back to Top