Galactosemia

Galactosemia
Classification and external resources
Galactose
ICD-10	E74.2
ICD-9	271.1
eMedicine	ped/818
MeSH	D005693

Galactosemia (British Galactosaemia) is a rare genetic metabolic disorder that affects an individual's ability to metabolize the sugar galactose properly. Although the sugar lactose can metabolize to galactose, galactosemia is not related to and should not be confused with lactose intolerance. Galactosemia follows an autosomal recessive mode of inheritance that confers a deficiency in an enzyme responsible for adequate galactose degradation.

Goppert first described the disease in 1917,^[1] with its cause as a defect in galactose metabolism being identified by a group led by Herman Kalckar in 1956.^[2]

Its incidence is about 1 per 60,000 births. Galactosemia is also very common within the Irish Traveller population.^[3]

Cause

• 

  Lactose

• 

  Glucose

• 

  Galactose

Lactose in food (such as dairy products) is broken down by the enzyme lactase into glucose and galactose. In individuals with galactosemia, the enzymes needed for further metabolism of galactose are severely diminished or missing entirely, leading to toxic levels of galactose 1-phosphate in various tissues as in the case of classic galactosemia, resulting in hepatomegaly (an enlarged liver), cirrhosis, renal failure, cataracts, brain damage, and ovarian failure. Without treatment, mortality in infants with galactosemia is about 75%.

Galactosemia is inherited in an autosomal recessive manner, meaning a child must inherit one defective gene from each parent to show the disease. Heterozygotes are carriers, because they inherit one normal gene and one defective gene.^[4] Carriers show no symptoms of galactosemia.

Types

Galactose is converted into glucose by the action of three enzymes, known as the Leloir pathway. Accordingly, there are 3 known types of Galactosemia; type 1, 2 and 3:

Type	Diseases Database	OMIM	Gene	Locus	Enzyme	Name
Type 1	5056	230400	GALT	9p13	galactose-1-phosphate uridyl transferase	classic galactosemia
Type 2	29829	230200	GALK1	17q24	galactokinase	galactokinase deficiency
Type 3	29842	230350	GALE	1p36-p35	UDP galactose epimerase	galactose epimerase deficiency, UDP-Galactose-4-epimerase deficiency

The order of these three types is not the same as the order that the enzymes are encountered by galactose on its metabolic path (which is closer to GALK, GALT, and then GALE, though many variations can occur.)^{[citation needed]}

Accumulation of galactose

Reduction to galactitol

In galactosemic patients, the accumulation of galactose becomes the substrate for enzymes that catalyze the polyol pathway of carbohydrate metabolism. The first reaction of this pathway is the reduction of aldoses, types of sugars including galactose, to sugar alcohols.^[5] Recent data suggests that aldose reductase is the enzyme responsible for the primary stage of this pathway. Therefore aldose reductase reduces galactose to its sugar alcohol form, galactitol. Galactitol, however, is not a suitable substrate for the next enzyme in the polyol pathway, polyol dehydrogenase. Thus, galactitol accumulates in body tissues and is excreted in the urine of galactosemic patients. Accumulation of galactitol has been attributed to many of the negative effects of galactosemia, and high concentrations of galactitol have been found in people with classic galactosemia (GALT deficiency), galactokinase deficiency, and epimerase deficiency.

Oxidation to galactonate

Accumulated galactose can also undergo an alternative reaction: oxidation to galactonate. The mechanism of galactonate formation is still unclear. However, recent studies suggest that galactose dehydrogenase is responsible for converting galactose to galactonolactone, which then spontaneously or enzymatically converts to galactonate. Once formed, galactonate may enter the pentose phosphate pathway. Thus, oxidation to galactonate serves as an alternate form of metabolizing galactose. This oxidative pathway renders accumulated galactonate less harmful than accumulated galactitol.

Diagnosis

Infants routinely screened for galactosemia in the United States, and the diagnosis is made while the person is still an infant. Infants affected by galactosemia typically present with symptoms of lethargy, vomiting, diarrhea, failure to thrive, and jaundice. None of these symptoms are specific to galactosemia, often leading to diagnostic delays. Luckily, most infants are diagnosed on newborn screening. If the family of the baby has a history of galactosemia, doctors can test prior to birth by taking a sample of fluid from around the fetus (amniocentesis) or from the placenta (chorionic villus sampling or CVS).^[6]

A galactosemia test is a blood test (from the heel of the infant) or urine test that checks for three enzymes that are needed to change galactose sugar that is found in milk and milk products-into glucose, a sugar that your body uses for energy. A person with galactosemia doesn't have one of these enzymes. This causes high levels of galactose in the blood or urine.

Galactosemia is normally first detected through newborn screening, or NBS. Affected children can have serious, irreversible effects or even die within days from birth. It is important that newborns be screened for metabolic disorders without delay. Galactosemia can even be detected through NBS before any ingestion of galactose-containing formula or breast milk.

Detection of the disorder through newborn screening (NBS) does not depend on protein or lactose ingestion, and, therefore, it should be identified on the first specimen unless the infant has been transfused. A specimen should be taken prior to transfusion. The enzyme is prone to damage if analysis of the sample is delayed or exposed to high temperatures. The routine NBS is accurate for detection of galactosemia. Two screening tests are used to screen infants affected with galactosemia - the Beutler's test and the Hill test. In fact a third test, called the "Florida test", is also normally performed on all galactosemia positives. The Beutler's test screens for galactosemia by detecting the level of enzyme of the infant. Therefore, the ingestion of formula or breast milk does not affect the outcome of this part of the NBS, and the NBS is accurate for detecting galactosemia prior to any ingestion of galactose.

Treatment

The only treatment for classic galactosemia is eliminating lactose and galactose from the diet. Even with an early diagnosis and a restricted diet, however, some individuals with galactosemia experience long-term complications such as speech difficulties, learning disabilities, neurological impairment (e.g. tremors, etc.), and ovarian failure in females. Symptoms have not been associated with Duarte galactosemia, and many individuals with Duarte galactosemia do not need to restrict their diet at all. Infants with classic galactosemia cannot be breast-fed due to lactose in human breast milk and are usually fed a soy-based formula.^[7]

Galactosemia is sometimes confused with lactose intolerance, but galactosemia is a more serious condition. Lactose intolerant individuals have an acquired or inherited shortage of the enzyme lactase, and experience abdominal pains after ingesting dairy products, but no long-term effects. In contrast, a galactosemic individual who consumes galactose can cause permanent damage to their bodies.

Long term complication of galactosemia includes:

• Speech deficits
• Ataxia
• Dysmetria
• Diminished bone density
• Premature ovarian failure
• Cataract

Recent Research

The gene mapping using the discovery of specialized transduction has been used to gain a better understanding of the genetic errors involved in galactosemia. Galactosemia is now understood to be due to a collection of possible genetic mutations. A collection of correspondence can now be examined.[.^[8] Also see Wikipedia entries for Esther Lederberg and Larry Morse. ^{[9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]}

See also

• Galactosemic cataract

References

1. ^ Goppert F. Galaktosurie nach Milchzuckergabe bei angeborenem, familiaerem chronischem Leberleiden. Klin Wschr 1917;54:473-477.
2. ^ Isselbacher KJ, Anderson EP, Kurahashi K, Kalckar HM (1956). "Congenital galactosemia, a single enzymatic block in galactose metabolism". Science 13 (123): 635–6. doi:10.1126/science.123.3198.635. PMID 13311516. 
3. ^ Miriam Murphy, Brian McHugh, Orna Tighe, Philip Mayne, Charles O'Neill, Eileen Naughten and David T Croke. Genetic basis of transferase-deficient galactosaemia in Ireland and the population history of the Irish Travellers. European journal of Human Genetics. July 1999, Volume 7, Number 5, Pages 549-554.
4. ^ Galactosemia The University of Utah, Genetics Science Learning Center. 2008.
5. ^ Kolatkar, Nikheel Dr. "Aldose Rudctase Inhibitors." Your Total Health. http://yourtotalhealth.ivillage.com/aldose-reductase-inhibitors.html
6. ^ Fensom AH, Benson PF, Blunt S (November 1974). "Prenatal diagnosis of galactosaemia". Br Med J 4 (5941): 386–7. doi:10.1136/bmj.4.5941.386. PMC 1612460. PMID 4154122. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1612460. 
7. ^ Breastfeeding: Diseases and Conditions: Contraindicators | DNPA
8. ^ click on Galactosemia
9. ^ "Genetic transduction in Escherichia coli", Doctoral dissertation, M. L. Morse, University of Wisconsin, 1955
10. ^ "Cis-Trans position effect in transduction heterogenotes of Escherichia coli", by Morse, M. L., Genetics 40: 586-587, 1955
11. ^ "Transduction in Escherichia coli K-12", by Morse, M. L., E. M. Lederberg, and J. Lederberg, Genetics 41(1): 142-156, Jan., 1956
12. ^ "Transductional heterogenotes in Escherichia coli", by Morse, M. L., E. M. Lederberg, and J. Lederberg, Genetics 41(5): 758-779, Sept. 1956
13. ^ "Transduction and transformation", by Morse, M. L., and M. L. Alire, Annals of the New York Academy of Sciences, 68(2): 324-334, Oct. 21, 1957
14. ^ "Recombination and segregation in Gal heterogenotes showing position effect", by Morse, M. L., Genetics, 44: 529, 1959
15. ^ "TRANSDUCTION BY STAPHYLOCOCCAL BACTERIOPHAGE", by Morse, M. L., Proceedings of the National Academy of Sciences USA", 45(5): 722-727, May, 1959
16. ^ "FURTHER STUDIES OF SOME GALACTOSE MUTANTS OF e. COLI k-12", by Morse, M. L., Biophysical Society Fifth Annual Meeting (abstract), 1961
17. ^ "CHARACTERISTICS OF A STAPHYLOCOCCAL PHAGE CAPABLE OF TRANSDUCTION", by Morse, M. L., Journal of Bacteriology, 83(4): 775-780, April, 1962
18. ^ "Mapping studies of galactose mutants of Escherichia coli K-12", by Morse, M. L., Genetics, 45, 1001, 1960 and PNAS, Aug., 1962
19. ^ "SPONTANEOUS PRODUCTION OF LAMBDA PARTICLES WITH TRANSDUCING ACTIVITY", by Morse, M. L., Genetics, 47(2): 255-260, February, 1962
20. ^ "Galactose Mutants of E. coli not Serving as Recipients in Lambda Transduction", by Morse, M. L., Biophysical Society Sixth Annual Meeting, 1962
21. ^ "Reverse Mutation Among Galactose Mutations of E. coli K-12", by Morse, M. L., Bacteria Proceedings (abstract), p. 42, 1962
22. ^ "Galactose Mutations of Escherichia Coli K-12 Not Amenable to Lambda Transduction", by Morse, M. L. and J. W. Labelle, Genetics 48(6): 835-840, June, 1963
23. ^ "Symposium on Bacterial and Viral Genetics (Canberra, August 1957)", by Lederberg, J., B. W. Holloway, E. M. Lederberg, F. M. Burnet, F. Fenner, and R. J. Best, Australian Journal of Science 20:71-76, August, 1957
24. ^ "Fine structure of Gal loci in Escherichia coli K-12", by Lederberg, E., Tenth International Congress of Genetics, Montreal, 1958
25. ^ "Genetic and functional aspects of galactose metabolism in Escherichia coli K-12", by Lederberg, E. M., Microbial Genetics, Tenth Symposium, Soc. Gen. Microbiol., Great Britain, p. 115, 1960
26. ^ "Interaction of streptomycin and a suppressor for galactose fermentation in E. coli K-12", by Lederberg, E. M., L. L. Cavalli-Sforza, and J. Lederberg, Proceedings of the National Academy of Sciences, U. S., 51:678-682, April, 1964

External links

• Galactosemia Resources and Information
• Parents of Galactosemic Children, Inc. website
• What is Galactosemia?
• Galactosemic Families of Minnesota
• Galactosemia Handbook - A Guide for Families
• galactosemia.org
• GeneReviews/NIH/UW entry on Galactosemia
• OMIM entries on Galactosemia
• GeneReviews/NCBI/NIH/UW entry on Epimerase Deficiency Galactosemia
• OMIM entries on Epimerase Deficiency Galactosemia