Galactosemia

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This entry is adapted from the peer-reviewed paper https://medlineplus.gov/genetics/condition/galactosemia

Galactosemia is a disorder that affects how the body processes a simple sugar called galactose.

genetic conditions

1. Introduction

A small amount of galactose is present in many foods. It is primarily part of a larger sugar called lactose, which is found in all dairy products and many baby formulas. The signs and symptoms of galactosemia result from an inability to use galactose to produce energy.

Researchers have identified several types of galactosemia. These conditions are each caused by mutations in a particular gene and affect different enzymes involved in breaking down galactose.

Classic galactosemia, also known as type I, is the most common and most severe form of the condition. If infants with classic galactosemia are not treated promptly with a low-galactose diet, life-threatening complications appear within a few days after birth. Affected infants typically develop feeding difficulties, a lack of energy (lethargy), a failure to gain weight and grow as expected (failure to thrive), yellowing of the skin and whites of the eyes (jaundice), liver damage, and abnormal bleeding. Other serious complications of this condition can include overwhelming bacterial infections (sepsis) and shock. Affected children are also at increased risk of delayed development, clouding of the lens of the eye (cataract), speech difficulties, and intellectual disability. Females with classic galactosemia may develop reproductive problems caused by an early loss of function of the ovaries (premature ovarian insufficiency).

Galactosemia type II (also called galactokinase deficiency) and type III (also called galactose epimerase deficiency) cause different patterns of signs and symptoms. Galactosemia type II causes fewer medical problems than the classic type. Affected infants develop cataracts but otherwise experience few long-term complications. The signs and symptoms of galactosemia type III vary from mild to severe and can include cataracts, delayed growth and development, intellectual disability, liver disease, and kidney problems.

2. Frequency

Classic galactosemia occurs in 1 in 30,000 to 60,000 newborns. Galactosemia type II and type III are less common; type II probably affects fewer than 1 in 100,000 newborns and type III appears to be very rare.

3. Causes

Mutations in the GALT, GALK1, and GALE genes cause galactosemia. These genes provide instructions for making enzymes that are essential for processing galactose obtained from the diet. These enzymes break down galactose into another simple sugar, glucose, and other molecules that the body can store or use for energy.

Mutations in the GALT gene cause classic galactosemia (type I). Most of these genetic changes almost completely eliminate the activity of the enzyme produced from the GALT gene, preventing the normal processing of galactose and resulting in the life-threatening signs and symptoms of this disorder. Another GALT gene mutation, known as the Duarte variant, reduces but does not eliminate the activity of the enzyme. People with the Duarte variant tend to have much milder features of galactosemia.

Galactosemia type II results from mutations in the GALK1 gene, while mutations in the GALE gene underlie galactosemia type III. Like the enzyme produced from the GALT gene, the enzymes made from the GALK1 and GALE genes play important roles in processing galactose. A shortage of any of these critical enzymes allows galactose and related compounds to build up to toxic levels in the body. The accumulation of these substances damages tissues and organs, leading to the characteristic features of galactosemia.

4. Inheritance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

5. Other Names for This Condition

classic galactosemia
epimerase deficiency galactosemia
galactokinase deficiency disease
galactose epimerase deficiency
galactose-1-phosphate uridyl-transferase deficiency disease
GALE deficiency
GALK deficiency
GALT deficiency
UDP-galactose-4-epimerase deficiency disease
UTP hexose-1-phosphate uridylyltransferase deficiency

References

Berry GT. Classic Galactosemia and Clinical Variant Galactosemia. 2000 Feb 4[updated 2020 Jul 2]. In: Adam MP, Ardinger HH, Pagon RA, Wallace SE, Bean LJH,Stephens K, Amemiya A, editors. GeneReviews® [Internet]. Seattle (WA): Universityof Washington, Seattle; 1993-2020. Available fromhttp://www.ncbi.nlm.nih.gov/books/NBK1518/
Berry GT. Galactosemia: when is it a newborn screening emergency? Mol GenetMetab. 2012 May;106(1):7-11. doi: 10.1016/j.ymgme.2012.03.007.Review.
Bosch AM. Classical galactosaemia revisited. J Inherit Metab Dis. 2006Aug;29(4):516-25.
Fridovich-Keil J, Bean L, He M, Schroer R. Epimerase Deficiency Galactosemia. 2011 Jan 25 [updated 2016 Jun 16]. In: Adam MP, Ardinger HH, Pagon RA, WallaceSE, Bean LJH, Stephens K, Amemiya A, editors. GeneReviews® [Internet]. Seattle(WA): University of Washington, Seattle; 1993-2020. Available fromhttp://www.ncbi.nlm.nih.gov/books/NBK51671/
Fridovich-Keil JL, Gambello MJ, Singh RH, Sharer JD. Duarte VariantGalactosemia. 2014 Dec 4 [updated 2020 Jun 25]. In: Adam MP, Ardinger HH, PagonRA, Wallace SE, Bean LJH, Stephens K, Amemiya A, editors. GeneReviews®[Internet]. Seattle (WA): University of Washington, Seattle; 1993-2020. Availablefrom http://www.ncbi.nlm.nih.gov/books/NBK258640/
Fridovich-Keil JL, Gubbels CS, Spencer JB, Sanders RD, Land JA, Rubio-Gozalbo E. Ovarian function in girls and women with GALT-deficiency galactosemia. JInherit Metab Dis. 2011 Apr;34(2):357-66. doi: 10.1007/s10545-010-9221-4.
Karadag N, Zenciroglu A, Eminoglu FT, Dilli D, Karagol BS, Kundak A, Dursun A,Hakan N, Okumus N. Literature review and outcome of classic galactosemiadiagnosed in the neonatal period. Clin Lab. 2013;59(9-10):1139-46. Review.
Openo KK, Schulz JM, Vargas CA, Orton CS, Epstein MP, Schnur RE, Scaglia F,Berry GT, Gottesman GS, Ficicioglu C, Slonim AE, Schroer RJ, Yu C, Rangel VE,Keenan J, Lamance K, Fridovich-Keil JL. Epimerase-deficiency galactosemia is not a binary condition. Am J Hum Genet. 2006 Jan;78(1):89-102.
Timson DJ. The molecular basis of galactosemia - Past, present and future.Gene. 2016 Sep 10;589(2):133-41. doi: 10.1016/j.gene.2015.06.077.

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Camila Xu

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Table of Contents

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1. Introduction

2. Frequency

3. Causes

4. Inheritance

5. Other Names for This Condition

References

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1. Introduction

2. Frequency

3. Causes

3.1. The genes associated with Galactosemia

4. Inheritance

5. Other Names for This Condition

References