Tay-Sachs disease

Genetics, Metabolic Disorders No Responses »
Aug 122011
The most common of the lipid storage diseases, Tay-Sachs disease results from a congenital deficiency of the enzyme hexosaminidase A. It’s characterized by progressive mental and motor deterioration and is usually fatal before age 5, although some adolescents and adults with variations of hexosaminidase A deficiency have been noted.
Causes
Tay-Sachs disease (also known as GM2 gangliosidosis) is an autosomal recessive disorder in which the enzyme hexosaminidase A is virtually absent or deficient. This enzyme is necessary for metabolism of gangliosides, water-soluble glycolipids found primarily in central nervous system (CNS) tissues. Without hexosaminidase A, accumulating lipid pigments distend and progressively destroy and demyelinate CNS cells.
Tay-Sachs disease strikes persons of Eastern European Jewish (Ashkenazi) ancestry more often than the general population, occurring in about 1 in 2,500 live births in this ethnic group. About 1 in 25 Ashkenazi Jews are heterozygous carriers.
Signs and symptoms
A neonate with classic Tay-Sachs disease appears normal at birth, although he may have an exaggerated Moro reflex. By age 3 to 6 months, he becomes apathetic and responds only to loud sounds. His neck, trunk, arm, and leg muscles grow weaker, and soon he can’t sit up or lift his head. He has difficulty turning over, can’t grasp objects, and has progressive vision loss.
By age 18 months, the infant is usually deaf and blind and has seizures, generalized paralysis, and spasticity. His pupils are dilated and don’t react to light. Decerebrate rigidity and a vegetative state follow. The child suffers recurrent bronchopneumonia after age 2 and usually dies before age 5. A child who survives may develop ataxia and progressive motor retardation between ages 2 and 8.
The “juvenile” form of Tay-Sachs disease generally appears between ages 2 and 5 as a progressive Continue reading »
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Reye's syndrome

Liver Diseases, Metabolic Disorders No Responses »
Aug 092011
An acute childhood illness, Reye’s syndrome causes fatty infiltration of the liver with concurrent hyperammonemia, encephalopathy, and increased intracranial pressure (ICP). In addition, fatty infiltration of the kidneys, brain, and myocardium may occur.
Reye’s syndrome affects children. It’s most common in patients ages 4 to 12, with a peak incidence at age 6.
The prognosis depends on the severity of central nervous system depression. Previously, mortality was as high as 90%. Today, ICP monitoring and, consequently, early treatment of increased ICP, along with other treatment measures, have cut mortality to about 20%. Death is usually a result of cerebral edema or respiratory arrest. Comatose patients who survive may have residual brain damage.
Causes
Incidence of Reye’s syndrome usually rises during influenza outbreaks and is linked to aspirin use. It almost always follows within 1 to 3 days of an acute viral infection, such as an upper respiratory tract infection, type B influenza, or varicella (chickenpox).
With Reye’s syndrome, damaged hepatic mitochondria disrupt the urea cycle, which normally changes ammonia to urea for its excretion from the body. This results in hyperammonemia, hypoglycemia, and an increase in serum short-chain fatty acids, leading to encephalopathy. Simultaneously, fatty infiltration is found in renal tubular cells, neuronal tissue, and muscle tissue, including the heart.
Signs and symptoms
Reye’s syndrome develops in five stages, but the severity of the child’s signs and symptoms varies with the degree of encephalopathy and cerebral edema. Infants may have atypical presentation.
After the initial viral infection, a brief recovery period follows when the child doesn’t seem seriously ill. A few days later, he develops intractable vomiting, lethargy, rapidly changing mental status (mild to severe agitation, confusion, irritability, delirium), hyperactive reflexes, and rising blood pressure, respiratory rate, and pulse rate.
Reye’s syndrome may progress to coma. As the coma deepens, seizures develop, followed by decreased tendon reflexes and, commonly, respiratory failure. Continue reading »
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Hyponatremia (Water Intoxication)

Metabolic Disorders No Responses »
Jan 082011
Definitions
  • Hyponatremia is defined as a serum sodium of <135 mEq/L.
  • Water intoxication is defined as an “acute neurologic disturbance that results from rapid, excessive water intake.” The associated rapid decrease in sodium can result in lethargy, seizures, coma, and death.
Epidemiology and Etiology
  • Forty percent of children in children’s hospitals have a serum sodium of <135 mEq/L as a result of chronic illness. They are asymptomatic and do not require special intervention.
  • Causes of water intoxication include excessive parenteral or enteral water administration by medical personnel, excessive oral ingestion of water in an infant, repeated immersion, and excessive voluntary oral ingestion of water.
  • During a review of 34 patients with water intoxication at St. Louis Children’s Hospital between January 1975 and July 1990, investigators found that excessive water was usually ingested with a bottle. There were multiple reasons given for giving the infants excessive water, including “ran out of formula, gave water for diarrhea, and gave water for irritability or fussiness.”
Clinical Presentation and Physical Examination
  • Clinical presentation: 3- to 6-month-old infant who presents with apnea or seizures
  • Physical examination
    • Careful neurologic examination, including evaluating mental status
    • Low body temperature despite warm summer environment

Treatment
  • Central pontine myelinolysis occurs from rapid correction of chronic hyponatremia. The Continue reading »
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