Introduction:
Galactokinase deficiency is also known as galactosemia type 2. It is an inherited disorder in the metabolism of galactose sugar in the body. It is a rare disorder. Galactose is produced in the body as well as consumed through dairy products. It is a part of lactose sugar which is a complex sugar. It is one of the types of galactosemia which are a total of three types.
How Does Galactokinase Deficiency Occur?
Firstly it is important to understand the normal pathway of galactose metabolism to understand the pathology better. The normal process of galactose metabolism starts with the phosphorylation of galactose which is produced inside and outside the body by the enzyme galactokinase (GALK 1) into galactose-1-phosphate. Galactose 1 phosphate in reaction with UDP-glucose produces glucose-1 -phosphate, and UDP-galactose with the help of galactose-1-phosphate uridylyltransferase. UDP-glucose may get converted into UDP-galactose by the UDP galactose-4’-epimerase (GALE) reaction. This whole pathway is called the Leloir pathway.
Along with these major pathways, some minor reactions exist. They are the conversion of galactose to galactonate by the enzyme galactose dehydrogenase and the conversion of galactose to galactitol by aldose reductase. The little pathways do not function when the minor pathways are functioning. The major pathways work actively (GALK, GALT, GALE) when minor pathways do not work. But when those major pathways get blocked minor pathways get activated. There is an accumulation of galactitol in the body due to the blockage of major pathways.
What Is the Cause of Galactokinase Deficiency?
The deficiency of the galactokinase enzyme is caused due to the mutation of the GALK 1 gene which codes for the galactokinase enzyme and is located on chromosome 17q24. It is inherited as an autosomal recessive trait. That means when each parent passes one copy of their defective gene to the child, the child receives two copies of the defective gene and hence is affected by the disease. The parents of the child are called carriers because they carry the mutated gene but do not exhibit the signs and symptoms of the disease. So with each pregnancy, there is a 25 percent chance of a child getting affected by the disease and 25 percent of not getting affected by the disease, and 50 percent of the child being a carrier of the disease like the parents.
What Are the Signs and Symptoms of Galactokinase Deficiency?
The signs and symptoms of the disorder issue to the accumulation of galactitol which is an alcoholic derivative. This alcohol derivative is toxic to the body since it starts to accumulate in various body parts due to the failure of the breakdown of galactose. The symptoms are:
1. Cataracts: The accumulated galactitol gets deposited in the lens causing osmotic swelling of fibers of the lens, cell membrane rupture, and protein denaturation.
2. Delay in Child Development: There is a delay in achieving the appropriate height and weight according to age. There is the presence of small-sized reproductive parts (testes and ovaries).
3. Neurological Impairment: The child will have pseudotumor cerebri which means pressure around the structure of the brain. This will resemble pressure due to a large brain tumor and will lead to changes in vision, ringing in the ears, and nausea. But this pressure is due to the deposition of galactitol in the cerebrospinal fluid around the spinal cord and the brain.
4. Others
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Intellectual impairment.
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Difficulty in speech.
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Difficulties in motor skills.
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Renal disease.
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Premature ovarian insufficiency.
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Sepsis.
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Presence of a small-sized head.
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These symptoms are seen in children. Some of the symptoms seen in adults are hormonal issues like primary ovarian insufficiency, caused in women. It makes it difficult for them to get pregnant.
What Is the Diagnosis of Galactokinase Deficiency?
1. Newborn Screening - It is done to detect any abnormality. Newborns with cataracts and galactosemia should be evaluated for galactokinase deficiency. The newborn screening tests include fluorometric or bacterial inhibition assay to measure the total galactose and Beutler fluorescent spot test.
2. GALT Enzyme Analysis - It is done in a newborn with the doubt of galactosemia because of clinical symptoms suggestive of galactokinase deficiency. If the GALT level is less than 24.5nmol/h/mg of the hemoglobin, it indicates either classical galactosemia (galactosemia type 1 due to mutations in the GALT gene) and Duarte-variant galactosemia (galactosemia type 2 caused due to mutation of the GLAK 1 gene). GALT gene analysis is done after these test results. And if the GALT level is more than 24.5 nmol/h/mg of hemoglobin and if the total galactose level is elevated then galactose-1-phosphate levels are measured. When the levels are normal enzyme assay of galactokinase is done.
3. Other Tests
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Urine and serum have elevated levels of galactose and galactitol. But with diet restrictions, their levels are normal or decreased.
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Ophtlamalthic examination of the cataract in newborns can help diagnose galactokinase deficiency.
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Gene sequencing can also help in detecting the deficiency of galactokinase.
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Women with the risk of having a child with galactosemia can undergo prenatal testing by amniocentesis or chorionic villus sampling or preimplantation genetic testing.
What Is the Treatment of Galactokinase Deficiency?
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As soon as there is an early diagnosis of galactokinase deficiency, there should be dietary restriction of galactose along with calcium supplementation. This can reduce the galactose levels in blood and urine to a significant level. Newborns can be switched to soy-based formulas instead of dairy products.
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If cataracts are treated as early as two or three weeks of age, the changes in the eyes can be reversed. When the cataracts are dense, surgical removal is required.
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A regular check-up with an ophthalmologist is required with a slit lamp to detect the development of cataracts.
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Blood glucose measurements are done due to the constant risk of hypoglycemia.
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Neurological development tests are done in patients with cognitive impairment.
What Are the Complications of Galactokinase Deficiency?
The most common complications are the development of cataracts and pseudotumor cerebri. Even though patients restrict galactose from their diet, our body naturally produces galactose which can not be eliminated. So patients can experience speech and learning difficulties, tremors, behavioral problems, ataxia (lack of balance and coordination), and hypogonadotropic hypogonadism.
Conclusion:
If the condition is diagnosed early and a galactose-free diet is followed, life expectancy is normal like a healthy person. But if there is serious damage to various organs in childhood, it may have a lifelong impact on health and life expectancy. It is managed by an integrated team consisting of a geneticist, pediatrician, neurologist, ophthalmologist, and neonatologist.
