Alpha thalassemia is an inherited blood disorder that affects hemoglobin. Hemoglobin is a protein found in red blood cells (RBCs) that makes it possible for RBCs to bind and carry oxygen throughout the body. Hemoglobin is made up of two different protein chains, which are referred to as alpha and beta chains (or alpha and beta globin). Alpha thalassemia is caused by harmful genetic changes (vari...

Beta globin-related hemoglobinopathies (including beta thalassemia and sickle cell disease) are a group of inherited blood disorders that affect hemoglobin, a major component of red blood cells that are responsible for carrying oxygen throughout the body. Hemoglobin is made up of two different protein chains, the alpha and beta chains. Harmful genetic changes in the HBB gene can result in reduce...

Bloom syndrome is an inherited disease that causes a person's chromosomes to break and rearrange frequently. Bloom syndrome is caused by mutations in the BLM gene. The chromosome instability seen in patients with Bloom syndrome causes high rates of cancer beginning in childhood or early adulthood. People with Bloom syndrome are usually smaller in stature than their peers and have a high-pitched ...

Canavan disease is an inherited condition that destroys the white matter that insulates nerve cells in the brain. This impairs the ability of nerve cells to communicate with other cells. Canavan disease is caused by harmful genetic changes (variants) in the ASPA gene that result in deficiency of the aspartoacylase enzyme. This enzyme breaks down a material called N-acetyl-L-aspartic acid (NAA) i...

Cystic Fibrosis (CF) is an inherited condition characterized by the production of abnormally thick, sticky mucus, particularly in the lungs and digestive system. It is caused by having at least two harmful genetic changes in the CFTR gene. Normally, the job of mucus is to protect and lubricate different organs. However, the thickened mucus produced by individuals with CF blocks and clogs various...

Dystrophinopathies are a group of conditions that generally cause muscle weakness. They are caused by harmful genetic changes (variants) in the DMD gene. There are two main forms of dystrophinopathies related to the DMD gene: Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD). DMD and BMD are inherited in an X-linked manner. This means the condition is typically more severe in...

Familial dysautonomia, caused by harmful genetic changes (mutations) in the ELP1 gene (formerly known as the IKBKAP gene), is an inherited condition that causes nerve cells to deteriorate. It affects the autonomic nervous system, which controls involuntary actions such as breathing, tear production, blood pressure, and body temperature. It also affects the sensory nervous system, which controls ...

Fanconi anemia is an inherited disorder in which the body cannot properly produce a protein that protects DNA from damage. This defective protein prevents the bone marrow from producing all types of blood cells. Without a sufficient number of red blood cells (anemia), the body does not receive enough oxygen, which can lead to abnormal bones and organs as well as developmental delay. A shortage o...

Fragile X syndrome (FXS), caused by extra CGG repeats in the FMR1 gene, is a condition that causes a variety of developmental and behavioral problems. Fragile X syndrome is the most common inherited form of intellectual disability. It is the leading single-gene cause of autism spectrum disorders. Fragile X syndrome is inherited in an X-linked manner. This means the condition is typically more se...

Gaucher disease is an inherited lysosomal storage disorder caused by harmful genetic changes (variants) in the GBA1 gene, formerly known as the GBA gene. The condition develops when the body fails to properly produce a particular enzyme to break down a fatty substance called glucocerebroside. Without this enzyme, glucocerebroside and several other associated substances will build up in the body...

Hexosaminidase A deficiency (HEX A deficiency), also known as Tay-Sachs disease, is caused by harmful genetic changes in the HEXA gene. It is a condition that mainly affects the nervous system. Individuals with Tay-Sachs disease do not have enough functional beta-hexosaminidase A enzyme. The beta-hexosaminidase A enzyme normally breaks down a substance called GM2 ganglioside. Without enough fun...

Mucolipidosis IV is an inherited lysosomal storage disorder caused by mutations in the MCOLN1 gene. Individuals with mucolipidosis IV lack an enzyme called mucolipin-1, which is important for the proper functioning of lysosomes, the digestive system of the cell, though its exact function is not fully understood. Mucolipidosis IV affects the development of the nerves. In about 15% of cases, it al...

Niemann-Pick disease (NPD), SMPD1-Related is an inherited disease in which the body cannot properly metabolize a certain fatty substance called sphingomyelin due to a deficient enzyme called acid sphingomyelinase. As a result, sphingomyelin builds up in the body, causing cells to die and making it harder for certain organs to work properly. Mutations in the SMPD1 gene can cause either the type A...

Spinal muscular atrophy (SMA) is a condition that causes a loss (atrophy) of motor neurons, which are specific nerves in the brain and spinal cord that control movement. It is caused by a deficiency of the SMN protein, which is most often the result of a deletion (or loss) of part of the SMN1 gene. Without motor neurons, messages cannot be passed from the brain to the muscles of the body. In sev...

15q11.2 deletion syndromes are caused by the loss of genetic material on chromosome 15. People typically inherit one copy of chromosome 15 from each parent. Missing the maternal copy leads to a condition called Angelman syndrome. If the paternal copy is missing, the condition is called Prader-Willi syndrome. Features of 15q11.2 deletion syndromes include delayed development, intellectual disabil...

22q11.2 deletion syndrome, also called DiGeorge syndrome, velocardiofacial syndrome, or conotruncal anomaly face syndrome, is a disorder that occurs when an individual is missing a portion of chromosome 22. Many different symptoms can occur with 22q11.2 deletion syndrome, and most individuals have some but not all of the symptoms. Common features include heart defects, a cleft palate, immune sy...

1p36 deletion syndrome is a disorder caused by a deletion of a small piece of chromosome 1. Common features of 1p36 deletion syndrome include moderate to severe intellectual disability, delayed growth, limited speech ability, and distinct facial features. Individuals with the condition may also have vision or hearing problems and abnormalities of the skeleton, heart, gastrointestinal system, kid...

4p deletion (Wolf-Hirschhorn syndrome) is caused by a deletion of a piece of chromosome 4. This missing genetic material results in severe developmental delays, a characteristic facial appearance, and multiple birth defects. These can include heart defects, hearing impairment, and eye problems. Most children who have 4p deletion (Wolf-Hirschhorn syndrome) have seizures. The incidence of 4p dele...

5p deletion syndrome (Cri du Chat) is caused by a deletion of a piece of chromosome 5. Signs and symptoms include a high-pitched cry, intellectual disability, distinctive facial features, small head size (microcephaly), low birth weight, and weak muscle tone (hypotonia) in infancy. Most individuals have difficulty with language. The symptoms vary among individuals. The incidence of 5p deletion...

Monosomy X, also known as Turner syndrome, is a condition that causes short stature, abnormal puberty, birth defects, and infertility in affected females. It is caused by a difference in the number of sex chromosomes. Females typically have two X chromosomes, while males typically have one X and one Y chromosome. Turner syndrome occurs when a female has only one complete and functioning copy of...

Trisomy 13, also known as Patau syndrome, is a condition that causes severe intellectual disability and a wide range of birth defects. It occurs when there are three copies of chromosome 13 in the cells of the body instead of two. The symptoms seen in trisomy 13 are a result of this extra material impacting the growth and development of an affected individual. Common features of trisomy 13 inc...

Trisomy 18, also known as Edwards syndrome, is a condition that causes intellectual disability and a wide range of birth defects. It occurs when there are three copies of chromosome 18 in the cells of the body instead of two. The symptoms seen in trisomy 18 are a result of this extra material impacting the growth and development of an affected individual. Typical features of trisomy 18 inclu...

Trisomy 21, also known as Down syndrome, is a condition that causes intellectual disability and a wide range of medical problems. It occurs when there are three copies of chromosome 21 in the cells of the body instead of two. The symptoms seen in Down syndrome are a result of this extra material impacting the growth and development of an affected individual. The symptoms of Down syndrome vary g...

Trisomy X, also called Triple X syndrome, is caused by the presence of an extra 'X' chromosome, one of the sex chromosomes, in the body's cells. Individuals with trisomy X will present as typical females. Signs and symptoms vary between individuals, but are usually mild, if present. Because the symptoms are so mild, only about 10% of individuals with trisomy X will be diagnosed. Individuals with...

XXY, also known as Klinefelter syndrome, is a condition that causes physical and learning challenges in affected males. It is caused by a difference in the number of sex chromosomes. Females typically have two X chromosomes, while males typically have one X and Y chromosome. Klinefelter syndrome is caused when a male has two copies of the X chromosome and one Y chromosome. The symptoms of Klinef...

XYY, also known as Jacobs syndrome, is a condition that causes above average height and learning challenges in affected males. It is caused by a difference in the number of sex chromosomes. Females typically have two X chromosomes, while males typically have one X and one Y chromosome. XYY is caused when a male has two copies of the Y chromosome in the cells of the body instead of one. The sympt...