Diseases

X-Linked Agammaglobulinemia

X-linked agammaglobulinema is a genetic condition that affects the immune system and occurs almost exclusively in males. Affected individuals have very few B cells in the body, which produce antibodies called immunoglobulins that help protect the body against infection. Those with this condition are more susceptible to infections because their body makes very few of these antibodies.This condition is inherited in an X-linked recessive pattern and is caused by mutations in the BTK gene. 

It occurs in a frequency of about 1 in 100,000 male newborns, and has no ethnic predisposition. XLA is treated by infusion of human antibody. Treatment with pooled gamma globulin cannot restore a functional population of B cells, but it is sufficient to reduce the severity and number of infections due to the passive immunity granted by the exogenous antibodies.

X-Linked Cobalamin Disorder

Obtained from foods such as milk, eggs, fish and meat, B 12 is essential to human health because it helps the body convert food into fuel. It's vital to the nervous system and for making red blood cells.

Derivatives of vitamin B12 (cobalamin) are essential cofactors for enzymes required in intermediary metabolism. Defects in cobalamin metabolism lead to disorders characterized by the accumulation of methylmalonic acid and/or homocysteine in blood and urine. 

X-linked Hypohidrotic Ectodermal Dysplasia

X-linked hypohidrotic ectodermal dysplasia (XLHED) is a rare genetic disorder. Children born with XLHED have a reduced ability to sweat (hypohidrosis), abnormally shaped and missing teeth (hypodontia), and fine sparse hair (hypotrichosis). There are a number of additional features of XLHED, which may include dry eyes, eczema, asthma, and dry mucous membranes in the mouth and nose.

 

In the first years of life, children with XLHED are at risk for severe medical complications. These complications are most often associated with their inability to sweat, which can lead to their bodies overheating. Children with XLHED also have reduced mucous secretion and may be more prone to respiratory infections. Throughout childhood the focus of care may shift to chronic skin issues, medical management, and self-esteem challenges of severe hypodontia—missing and pointed teeth. Dentures may be prescribed as early as age 2-3 years to enhance feeding and growth and to begin to address what are often life-long psychosocial issues.

Incidence

The worldwide incidence of XLHED is estimated to be between 4 to 10/100,000 male births (as many as 200 births annually). Additionally, about 50% of XLHED-carrier females (approximately 400 births annually) are estimated to have symptoms that would warrant therapeutic intervention.

 

X-linked ichthyosis

X-linked ichthyosis: A rare genetic skin disorder occurring in males only and resulting from an inborn error of metabolism (deficiency of the enzyme steroid sulfatase).

X-linked Juvenile Retinoschisis

X-linked juvenile retinoschisis (XLRS) is a genetic ocular disease characterized by reduced visual acuity in males due to juvenile macular degeneration.

X-linked lymphoproliferative syndrome

X-linked lymphoproliferative syndrome (XLP) is an inherited disorder of the immune system that affects males. XLP is characterized by an abnormal immune response to infection with the Epstein-Barr virus (EBV). This is a common virus in the normal population, which causes infectious mononucleosis (“mono or kissing disease”). In normal individuals, EBV causes no long lasting ill effects. In individuals with X-linked lymphoproliferative syndrome, there is a mutation (mistake) in the XLP gene, SH2D1A/DSHP/SAP. This gene helps control the immune response to an EBV infection. As a result, males with XLP who are exposed to the EBV virus can have life-threatening symptoms. Patients with the disorder, in the absence of an acute EBV infection, are also subject to immune system problems, including recurrent infections and an unusual susceptibility to B-cell lymphomas. The diagnosis is confirmed by mutation detection (laboratory tests looking for a mistake in the XLP gene).

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X-linked mental retardation and macro-orchidism

Mental retardation, X-linked - macrocephaly - macro-orchidism: A rare disorder characterized by mental retardation, enlarged testes and a large head. Not all patients will exhibit all of these symptoms.

X-linked mental retardation craniofacial abnormal microcephaly club

X-linked mental retardation craniofacial abnormal microcephaly club: A rare inherited disorder characterized by mental retardation, small head, club foot and facial and skull abnormalities. The condition is inherited in a X-linked manner and thus only males present with the full severity of the symptoms. Female carriers may be mildly symptomatic or have no symptoms at all.

X-linked mental retardation type Wittwer

Mental retardation, X-linked, Wittwer type: A rare disorder characterized by severe mental retardation, retarded growth, seizures and vision and hearing problems. The disorder is inherited in a X-linked manner which means that only males display the full range of symptoms whereas female carriers may have mild or no symptoms.

X-Linked Myotubular Myopathy

X-linked myotubular myopathy is a condition that primarily affects muscles used for movement (skeletal muscles) and occurs almost exclusively in males.

Because of their severe breathing problems, individuals with X-linked myotubular myopathy usually survive only into early childhood; however, some people with this condition have lived into adulthood.

X-linked myotubular myopathy is a member of a group of disorders called centronuclear myopathies. In centronuclear myopathies, the nucleus is found at the center of many rod-shaped muscle cells instead of at either end, where it is normally located.

The incidence of X-linked myotubular myopathy is estimated to be 1 in 50,000 newborn males worldwide.

X-linked Retinitis Pigmentosa

X-linked retinitis pigmentosa (XLRP) is a severe, incurable genetic eye disease that causes progressive vision loss, primarily in males, leading to legal blindness by the mid-40s. Caused by mutations in the RPGR gene on the X chromosome, it results in the death of retinal cells and the degeneration of photoreceptors, starting with night blindness and progressing to tunnel vision. While there is no cure, gene therapy is a promising emerging treatment, and management focuses on low-vision aids, rehabilitation, and support.

X-linked sideroblastic anemia

X-linked sideroblastic anemia: A very rare, inherited form of anemia where red blood cells are unable to use iron properly to make hemoglobin which is needed to enable the blood to carry oxygen. This causes the body to absorb more iron from food and the excess iron collects in various parts of the body where it causes damage.

X-linked Tetra-amelia

X linked tetra-amelia is listed as a "rare disease" by the Office of Rare Diseases (ORD) of the National Institutes of Health (NIH). This means that X linked tetra-amelia, or a subtype of X linked tetra-amelia, affects less than 2, people in the US population.

Xanthinuria

Xanthinuria, which was first described by Dent and Philpot in 1954, is characterized by excretion of large amounts of xanthine in the urine and a tendency to form xanthine stones. Uric acid is strikingly diminished in serum and urine. Two clinically similar but distinct forms of xanthinuria are recognized. In type I there is an isolated deficiency of xanthine dehydrogenase, and in type II there is a dual deficiency of xanthine dehydrogenase and aldehyde oxidase (603592). Type I patients can metabolize allopurinol, whereas type II patients cannot. Xanthinuria also occurs in molybdenum cofactor deficiency.

Xanthogranulomatous cholecystitis

Xanthogranulomatous cholecystitis (medical condition): A lipid laden foam cell tumour of the gallbladder resulting in inflammation.

Xeroderma pigmentosum

Xeroderma pigmentosum (XP) is a rare autosomal recessive genetic disorder of DNA repair in which the ability to repair damage caused by ultraviolet (UV) light is deficient. In extreme cases, all exposure to sunlight must be forbidden, no matter how small; as such, individuals with the disease are often colloquially referred to as "children of the night". Multiple basal cell carcinomas (basaliomas) and other skin malignancies frequently occur at a young age in those with XP; metastatic malignant melanoma and squamous cell carcinoma[4] are the two most common causes of death in XP victims. This disease involves both sexes and all races, with an incidence of 1:250,000 in the United States. XP is roughly six times more common in Japanese people than in other groups.

Normally, damage to DNA in epidermal cells occurs during exposure to UV light. The absorption of the high-energy light leads to the formation of pyrimidine dimers, namely cyclobutane-pyrimidine dimers and pyrimidine-6-4-pyrimidone photoproducts. In a healthy, normal human being, the damage is first excised by endonucleases. DNA polymerase then repairs the missing sequence, and ligase "seals" the transaction. This process is known as nucleotide excision repair.

Xeroderma pigmentosum- type 1

Xeroderma pigmentosum, type 1: A rare genetic disorder where the enzyme that repairs DNA damage done by UV radiation is defective. It is characterized by sensitivity to sunlight, skin pigmentation and atrophy and actinic skin tumors. The different types of xeroderma pigmentosum vary in the body's ability to repair the damage to DNA done by UV radiation - type 1 has the lowest level of repair and the most neurological complications

Xeroderma pigmentosum- type 2

Xeroderma pigmentosum, type 2: A rare genetic disorder where the enzyme that repairs DNA damage done by UV radiation is defective. It is characterized by sensitivity to sunlight, skin pigmentation and atrophy and actinic skin tumors. The different types of xeroderma pigmentosum vary in the body's ability to repair the damage to DNA done by UV radiation. Type B is often associated with signs of Cockayne syndrome.

Xeroderma pigmentosum- type 3

Xeroderma pigmentosum, type 3: A rare genetic disorder where the enzyme that repairs DNA damage done by UV radiation is defective. It is characterized by sensitivity to sunlight, skin pigmentation and atrophy and actinic skin tumors. The different types of xeroderma pigmentosum vary in the body's ability to repair the damage to DNA done by UV radiation. Neurological symptoms are rarely experienced in type 3.