Galactosaemia

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Galactosaemia is also known as Galactose-1-Phosphate Uridyltransferase (GALT or GAL-1-PUT) Deficiency.

It is a rare inherited disorder.

  • Galactosaemia is the commonest carbohydrate metabolism disorder
  • Enzyme deficiency leads to hypergalactosaemia which has toxic effects


Galactosaemia should always be considered following:

  • E-Coli sepsis
  • Neonatal cataracts
  • Neonatal jaundice
  • Neonatal haemorrhage


See also the related articles:


Incidence

  • Incidence = 1 in 50 - 70 000
  • Age: presentation is invariably within the neonatal period.
  • Ethnicity: higher incidence in white populations


Aetiology

Image 1: Galactose Metabolism Pathway - click to enlarge

Galactosaemia is autosomal recessive


A variety of enzyme defects can lead to impaired Galactose metabolism:

  1. GAL-1-PUT deficiency is the commonest abnormality.
    1. The enzyme converts galactose-1-phosphate and UDP glucose to UDP galactose and glucose-1-phosphate.
    2. This defect leads to toxic hypergalactosaemia
    3. Caused by mutation in the GAL-1-PUT gene: Chromosome 9p13.
  2. Galactokinase converts galactose to galactose-1-phosphate and deficiency is less common.
  3. Uridine diphosphate (UDP) galactose-4-epimerase converts UDP galactose to UDP glucose and deficiency is again less common.


Sources of Galactose

Dietary: mainly dairy products, though also from sugar beet, gums and plant products.


Lactose, Lactase, Glucose and Galactose

Image 2: Lactose is a disaccharide of Glucose and Galactose - click to enlarge

Galactose is a monosaccharide.

  • When joined with Glucose it forms the disaccharide Lactose.
  • Lactose is hydrolysed in the gut by the enzyme Lactase (a beta-galactosidase).
    • Of note, Lactase is also produced by E-Coli.


Clinical features

Typical clinical features include:

  • Hepatomegaly usually with jaundice and coagulopathy
  • Cataracts
  • Developmental delay

History may reveal poor feeding, vomiting and poor weight gain. Cataracts may be apparent even in the early days of life.


Other features include:

  • Lethargy and hypotonia occur.
  • Sepsis (often with E. coli) can be fatal.
  • Ascites may even be apparent in early life.
  • Full fontanelle.
  • Developmental delay may affect speech, language and general learning.
  • In adults there is often short stature and there may be ataxia and tremor.
  • Hypergonadotrophic hypogonadism (women: premature ovarian failure / fertility unlikely)


Investigations

  • Urine Reducing Sugars
    • Lactose in milk will be hydrolysed in the gut into glucose and galactose (see Figure 2) and therefore be present in the urine.
    • Galactose may be present in the urine in any form of liver disease
  • Urine: albuminuria (early), generalised aminoaciduria (later)
  • Liver Function Tests - Hyperbilirubinaemia (initially unconjugated, later conjugated)
    • Hepatosteatosis and hepatits may occur early in the disease
    • Portal hypertension develops later. Cirrhosis is end-stage.
  • Gal-1-put erythrocyte assay
    • Assay may be erroneous if a blood transfusion has been administered - Gal-1-put testing on the parents can be undertaken.
    • Isoelectric focusing may distinguish variants.
    • Genotyping may allow molecular diagnosis
  • Ophthalmology - Slit Lamp Examination: screen for cataracts every 6 months until 3 years of age.
  • Metabolic acidosis
  • Haemolytic anaemia may occur


  • Raised serum phenylalanine may give a false positive test for phenylketonuria


Differential Diagnoses

  • Fructose-1-phosphate aldolase deficiency (fructose intolerance)
  • Galactokinase deficiency
  • Hereditary haemochromatosis
  • Alpha-1-antitrypsin deficiency
  • Sepsis
  • Tyrosinaemia
  • Mitochondrial disorders


Management

  • Lactose-containing milk should be discontinued to reduce immediate toxicity
    • Adults tolerate lactose better - lifelong dietary restriction is debated and usually advocated.
    • Not all features of the disease will be removed by this
    • Complete elimination of galactose from the diet is very difficult (sources include fruits and vegetables)
  • Treat sepsis
  • Treat Liver Disease
    • Vitamin K is likely to be required for coagulopathy
  • Dietician review
  • Endocrinology review (hypergonadotrophic hypogonadotrophism / ovarian failure)
  • Genetics review / Genetic Counselling
  • Speech Therapy
  • Education Support

Cataracts often reverse with dietary management.


Pregnancy with Galactosaemia

  • High levels of galactose in a pregnant women with galactosaemia does not appear to harm the foetus.
  • This contrasts with the situation in Phenylketonuria where diet in pregnancy must be very strictly managed.


Prognosis

Galactosaemia may be rapidly fatal


Morbidity and Mortality in early life stems from the presenting problems, particularly:

  • E-Coli sepsis
  • Liver disease / Coagulopathy


Antenatal Screening

See also the associated article:


Screening for Galactosaemia in the antenatal period is possible, though has not been adopted in the UK.

  • Austria, The Republic of Ireland and some States of the USA have screening programs.


References


Patient Support Information


See also the related articles:

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