Galactosemic Cataract - Types of Galactosemia and The Prevalence of Cataract

Types of Galactosemia and The Prevalence of Cataract

The presence of presenile cataract, noticeable in galactosemic infants as young as a few days old, is highly associated with two distinct types of galactosemia: GALT deficiency and to a greater extent, GALK deficiency.

An impairment or deficiency in the enzyme, galactose-1-phosphate uridyltransferase (GALT), results in classic galactosemia, or Type I galactosemia. Classic galactosemia is a rare (1 in 47,000 live births), autosomal recessive disease that presents with symptoms soon after birth when a baby begins lactose ingestion. Symptoms include life-threatening illnesses such as jaundice, hepatosplenomegaly (enlarged spleen and liver), hypoglycemia, renal tubular dysfunction, muscle hypotonia (decreased tone and muscle strength), sepsis (presence of harmful bacteria and their toxins in tissues), and cataract among others. The prevalence of cataract among classic galactosemics is markedly less than among galactokinase-deficient patients due to the extremely high levels of galactitol found in the latter. Classic galactosemia patients typically exhibit urinary galactitol levels of only 98 to 800 mmol/mol creatine compared to normal levels of 2 to 78 mmol/mol creatine.

Galactokinase (GALK) deficiency, or Type II galactosemia, is also a rare (1 in 100,000 live births), autosomal recessive disease that leads to variable galactokinase activity levels: ranging from high GALK efficiency to undetectably-low GALK efficiency. The early onset of cataract is the main clinical manifestation of Type II galactosemics, most likely due to the high concentration of galactitol found in this population. GALK deficient patients exposed to high-galactose diets show extreme levels of galactitol in blood and urine. Studies on galactokinase-deficient patients have shown that nearly two-thirds of ingested galactose can be accounted for by galactose and galactitol levels in the urine. Urinary levels of galactitol in these subjects approach 2500 mmol/mol creatine as compared to 2 to 78 mmol/mol creatine in control patients. A decrease in activity in the third major enzymes of galactose metabolism, UDP galactose-4’-epimerase (GALE), is the cause of Type III galactosemia. GALE deficiency is an extremely rare, autosomal recessive disease that appears to be most common among the Japanese population (1 in 23,000 live births among Japanese population). While the link between GALE deficiency and cataract prevalence seems to be ambiguous, experiments on this topic have been conducted. A recent 2000 study in Munich, Germany analyzed the activity levels of the GALE enzyme in various tissues and cells in patients with cataract. The experiment concluded that while patients with cataract seldom exhibited an acute decrease in GALE activity in blood cells, "the GALE activity in the lens of cataract patients was, on the other hand, significantly decreased." The study’s results are depicted below. The extreme decrease in GALE activity in the lens of cataract patients seems to suggest an irrefutable connection between Type III galactosemia and cataract development.

Read more about this topic:  Galactosemic Cataract

Famous quotes containing the words types of, cataract, prevalence and/or types:

    Our children evaluate themselves based on the opinions we have of them. When we use harsh words, biting comments, and a sarcastic tone of voice, we plant the seeds of self-doubt in their developing minds.... Children who receive a steady diet of these types of messages end up feeling powerless, inadequate, and unimportant. They start to believe that they are bad, and that they can never do enough.
    Stephanie Martson (20th century)

    The splendor falls on castle walls
    And snowy summits old in story;
    The long light shakes across the lakes,
    And the wild cataract leaps in glory.
    Blow, bugle, blow, set the wild echoes flying,
    Blow, bugle; answer, echoes, dying, dying, dying.
    Alfred Tennyson (1809–1892)

    The prevalence of suicide, without doubt, is a test of height in civilization; it means that the population is winding up its nervous and intellectual system to the utmost point of tension and that sometimes it snaps.
    Havelock Ellis (1859–1939)

    ... there are two types of happiness and I have chosen that of the murderers. For I am happy. There was a time when I thought I had reached the limit of distress. Beyond that limit, there is a sterile and magnificent happiness.
    Albert Camus (1913–1960)