OMIM ID:
Galactokinase Deficiency
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
This is a considerably more rare disorder of galactose metabolism compared with classic galactosemia (230400). Both disorders cause cataracts in the neonatal period but the early systemic effects of galactokinase deficiency are less severe. In the latter disorder, cataracts usually develop later, often during the first decade of life and less commonly during the neonatal period that is characteristic of classic galactosemia. Galactitol accumulation causing osmotic changes in the lens accounts for the cataracts and may also be responsible for the development of pseudotumor cerebri found infrequently. Good dietary control may prevent the formation and progression of cataracts and it has been reported that they may regress as well but only prior to the rupture of cell membranes.
Systemic Features
Late complications include abnormalities in mental and/or motor development, dyspraxia, and hypogonadotropic hypogonadism which occur in spite of severe reduction in galactose intake. Ovarian failure is common.
Genetics
Inheritance
This is an autosomal recessive disorder caused by mutations in the GALK1 gene (17q24) encoding galactokinase. It is extremely rare but should be considered in any patient with cataracts found within the first two decades of life. Deficient activity of the galactokinase enzyme can be demonstrated in erythrocytes.
For other disorders of galactose metabolism, see galactosemia (230400) and galactose epimerase deficiency (230350).
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.