Author: Glossary
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Hypoplastic left heart syndrome
Hypoplastic left heart syndrome (HLHS) describes a group of complex congenital heart defects that occur in newborns. HLHS is characterized by the underdevelopment of the left atrium and ventricle of the heart. Additionally, the valve that connects these two chambers (the mitral orifice) and the aortic valve are narrowed or closed. The defects on the…
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Hypohidrotic ectodermal dysplasia
Hypohidrotic ectodermal dysplasia (HED) is one of a diverse group of disorders that affect the skin and skin derivatives (teeth, hair, nails, sweat glands, and sebaceous glands). Disturbances in other organ systems are common in these diseases. The hallmarks of HED are a deficiency or complete absence of sweat glands, malformed or missing teeth, and…
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Hypochondroplasia
Hypochondroplasia is a rare, hereditary type of short- limbed dwarfism. Originally described in 1913, this disorder has many similarities to achondroplasia, with which it is, and has been, often confused. Physical findings in hypochondroplasia include short stature, mildly shortened extremities, malformed vertebrae of the lower spine, and nearly normal appearance of the face and head.…
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Hypertonia-rd
Hypertonia is increased tension of the muscles that can make movement difficult. It can also be defined as resistance to passive movement that is not velocity dependent. Hypertonia usually occurs in definite patterns of flexion or extension. Difficulties are most predominant in the flexor patterns for the upper extremities and in the extensor patterns of…
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Primary hypersomnia
Primary hypersomnia is a disorder characterized by excessive daytime sleepiness or extremely long periods of nighttime sleep (greater than 10 hours) on a regular basis. In the recurrent form of this disorder known as Kleine-Levin syndrome, symptoms occur for at least three days at a time and reoccur several times per year for two or…
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Hyperlexia
Hyperlexia is defined as the ability of an individual to recognize words at a level superior to that predicted by their age and measured intellectual ability, which is significantly better than their reading comprehension. The prevalence of hyperlexia is unknown, but as with most developmental disorders, it occurs three to four times as often in…
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Primary hyperhidrosis
Primary hyperhidrosis is a genetic disorder of hyperactivity of the sweat glands. Sweating may occur in the hands and feet, face, underarms, groin area, and under the breasts. Patients with more severe hyperhidrosis may experience excessive sweating all over the body. More common than primary hyperhidrosis, secondary hyperhidrosis develops because of an underlying disorder.
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Nonketotic hyperglycinemia
Nonketotic hyperglycinemia (NKH) is a rare autosomal- recessive trait involving an error of glycine metabolism. Large amounts of the amino acid glycine accumulate in the body fluids, particularly in the cerebrospinal fluid. Two subtypes of this disorder exist: nonclassic NKH and neonatal NKH. The former appears later in life and presents with milder neurological deficits…
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Hydrolethalus syndrome
Hydrolethalus syndrome is a recessively inherited lethal malformation syndrome involving the central nervous system. Prenatal diagnosis is most common, and the fetuses commonly present with hydrocephaly (with significant functional deficits), micrognathia (underdevelopment of the jaw), polydactyly (more than the normal number of fingers and toes), and a key-shaped defect of the occipital bone.
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X-linked hydrocephalus
Hydrocephalus is a condition that is caused by abnormal buildup or accumulation of cerebrospinal fluid (CSF) in the ventricles or subarachnoid space of the brain. As a result, intracranial pressure is increased by overproduction of CSF, obstruction of the flow of CSF, or failure to reabsorb the fluid. Hydrocephalus can be either congenital with an…