Galactokinase Deficiency
Patient Information
Characteristics
Background and History
This is one of several disorders of metabolism in galactose (sugar molecule found in many foods) which is not utilized properly as the result of a defective enzyme. This disorder is caused by a defect in the enzyme galactokinase and is considerably more rare and milder in its clinical effects compared to the condition called galactosemia.
Clinical Correlations
The most frequent clinical sign of galactokinase deficiency is cataracts which may be seen as early as the first decade of life but sometimes not until adulthood. However, in spite of dietary restrictions on lactose intake, some patients later in life have delayed growth and development, as well as difficulties with speech and muscle function.
Genetics
Inheritance
This is an autosomal recessive disorder in which the unaffected carrier parents each pass on a single copy of the mutation to their children. This creates a risk of an affected child of 25% for each pregnancy.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
Diagnosis and Prognosis
Galactokinase deficiency is suspected when cataracts are found in infants or young people. The diagnosis is made through detection of decreased activity of the enzyme in red blood cells.
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