Hailey–Hailey Disease is a rare genetic disorder that causes blisters to form on the skin.

Hajdu-Cheney Syndrome is a rare genetic disorder of the connective tissue.

Hallermann-Streiff Syndrome is a rare congenital disorder that affects growth, cranial development, hair growth and dental development.

Harboyan syndrome, also known as corneal dystrophy-perceptive deafness (CDPD), is an inherited, degenerative disorder characterized by congenital hereditary endothel...

Harding Ataxia is rare disorder characterized by progressive damage to the nervous system.

Harlequin syndrome is a rare disorder characterized by flushing and sweating on only one side of the face typically induced by heat or exercise.

Hartnup Syndrome is a rare autosomal recessive metabolic disorder affecting the absorption of neutral amino acids.

Heller's Syndrome is an extreme disorder that resembles autism. It is a disintegrative disorder that sets back the child's intelligence and social abilities.

Hemangiopericytomas are rare vascular tumors coming from cells associated with capillary walls. These tumors can be found throughout the body,most commonly in the lower extremities, pelvic area, ...

Hemochromatosis is a rare hereditary disease characterized by excessive absorption of dietary iron.

Hemoglobin Hasharon is a rare blood disorder.

Hemophilia is an inherited bleeding disorder which prevents the blood from clotting normally.

Heparin-induced thrombocytopenia is the development of thrombocytopenia due to the administration of heparin, an anticoagulant.

Hepatic Venoocclusive Disease is a disroder in which there is blockage of some of the small veins in the liver.

Hereditary Fructose Intolerance is a rare genetic disorder caused by a deficiency of liver enzymes that metabolise fructose.

A community for those affected by HHT. Hereditary Hemorrhagic Telangiectasia (HHT) is a genetic disorder that causes malformed blood vess...

Hereditary Inclusion Body Myopathies are a group of rare genetic disorders causing progressive muscle wasting and weakness beginning in young adults.

Multiple Hereditary Exostoses / Multiple Osteochondroma is a rare genetic bone condition in which multiple benign cartilage-capped bone tumors called exostoses / osteochondromas develop. They grow ...

Hereditary Pancreatitis is a condition characterized by recurrent episodes of pancreatic attacks.

Hereditary Renal Adysplasia is a disorder in which one kidney is absent and the other is very small and malformed.

Hereditary Spherocytosis is a genetic disorder characterized by the production of red blood cells that are more prone to hemolysis.

Hereditary Stomatocytosis describes a number of inherited disorders that affect the outer coating of the red blood cells.

Hermansky-Pudlak Syndrome is a rare form of albinism resulting in decreased pigmentation, platelet abnormality, legal blindness, and storage of an abnormal fat-protein compound.

Hidradenitis Suppurativa is a rare skin disease affecting areas bearing apocrine sweat glands and hair follicles.

HIDS is a periodic fever syndrome characterized by attacks of fever, arthralgia, skin lesions including cyclical mouth ulcers, and diarrhea.

Hirschsprung Disease is a rare disorder characterized by the enlargement of the colon due to bowel obstruction.

Histidinemia is a rare disorder caused by a deficiency of the enzyme histidase.

Hodgkin Lymphoma is a rare type of cancer originating from a type of white blood cells called lymphocytes.

Holocarboxylase synthetase deficiency is a disorder in which the body is unable to use the vitamin biotin effectively.

Holoprosencephaly is a rare disorder in which the brain does not develop into two hemispheres.

Holt-Oram Syndrome is a rare disorder characterized by limb abnormalities, affecting the bones in the wrist and commonly the heart.

Homocystinuria (HCU) is a rare disease characterized by an individual’s inability to process the amino acid methionine, which can cause harmful build-ups in the blood and urine. ...

Horner syndrome is a rare disorder characterized by damage to the sympathetic nerves of the face and eye.

Human T-Lymphotropic Virus is an RNA retrovirus that causes T-cell leukemia and T-cell lymphoma in adults.

Hunter Syndrome, also known as Mucopolysaccharidosis type II (MPS II...

Huntington's disease is a progressive brain disease characterized by the continuous loss of brain cells (neurons). Individuals with Huntington's Disea...

Hydrolethalus Syndrome is a rare genetic disorder characterized by improper fetal development.

Hyperacusis is a rare hearing disorder that causes sounds which would otherwise seem normal to most people to sound unbearably loud. People who suffer from hyperacusis may even find normal envir...

Hyperemesis Gravidarum is a rare and severe form of morning sickness characterized by nausea and vomiting during pregnancy that may require hospitalization.

Hyperhidrosis is a rare disorder characterized by excessive sweating on the palms of the hands, the soles of the feet, in the armpits, in the groin area, and/or under the breasts.

Hyperkalemic Periodic Paralysis is a rare inherited autosomal dominant disorder.

Hyperlipoproteinemia is the raised presence lipids in the blood.

Hyperoxaluria is a disorder characterized by excessive oxalate in the urine.

Hyperprolinemia is a condition which occurs when the amino acid proline is not broken down properly by the enzymes proline oxidase or pyrroline-5-carboxylate dehydrogense.

Hypersensitivity Pneumonitis is an inflammation of the lungs caused by hypersensitivity to inhaled organic dusts.

Hypochondroplasia is a developmental disorder classified as short-limbed dwarfism.

Hypokalemic Periodic Paralysis is a rare disorder characterized by muscle weakness or paralysis.

Hypomagnesemia with secondary hypocalcemia is an autosomal recessive genetic disorder affecting intestinal magnesium absorption.

H-ABC, for short.  Children and young adults with mutations of the TUBB4-4 gene.

Hypoparathyroidism is a rare disorder in which your body secretes abnormally low levels of parathyroid hormone which plays a key role in regulating and maintaining a balance of your body's levels o...

Hypophosphatasia is a rare metabolic bone disorder characterized by decreased tissue nonspecific alkaline phosphatase and defective bone mineralization.