Disaccharidases Deficiences

Question 1

How do Disaccharidase deficiency lead to Pathology?

Answer 1

• Increased osmotic load in small bowel
• Increased carbohydrate substrate
• Production of fatty acids, acetate, butyrate, hydrogen gas
• Bowel distention, abdominal pain, diarrhoea

Question 1

How does dissacharidase deficiency commonly occur?

Answer 1

• Most commonly secondary to GI diseas.
• Isolated enzyme defect is rare

Question 2

Why are biochemical tests not preferred for diagnosis of disacharidase deficiency?

Answer 2

• Poor diagnostic performance
• Challenging
• Rarely performed

Question 3

What are the types of Lactase Deficiency?

Answer 3

Primary

• Congenital
• Acquired
• Developmental (related to Prematurity)

Secondary

Question 4

What are features of congenital lactase deficiency?

Answer 4

• Rare, autosomal recessive disorder
• Severe presentation
• Histology and other enzymes normal

Question 5

What are features of Acquired lactase deficiency?

Answer 5

• Lactase falls with age
• Genetic basis

Question 6

What causes secondary lactase deficiency?

Answer 6

Intestinal Disease

• Flattening of villi causing lactose malabsorption
• Bacterial overgrowth in small intestine resulting in lactose fermentation
• Other disaccharidases affected but less reserve of lactase

Question 7

How is the diagnosis of lactase deficiency made?

Answer 7

1. Clinical​​
   
   • Symptoms resolve after lactose avoidance
   • Formal lactose provocative test
2. Hydrogen breath test​​
   
   • Histological examination
   • Enzyme analysis
   • Relies on biopsy quality
3. Small bowel biopsy
4. Genetic testing
   
   • ​​Primary enzyme deficiency
5. Analysis of faeces

Question 8

What are tests for faecal analysis?

Answer 8

Tests using Faecal reducing substances

1. Benedict’s test
   
   • Reduction of Cu2+ ions
   • Colour change noted
   • Detects all sugars
2. Thin layer chromatography

Question 9

What are limitations of tests using faeal reducing substances?

Answer 9

• Lack of sensitivity and specificity
• Quality of the sample (uniformity, timing)
• False negative results: Bacterial degradation of disaccharides on sample storage
• False positive results: Lactose may be present in unaffected patients with diarrhoea
• Subjective
• Technical difficulties: IQC, EQA, UKAS
• Most UK laboratories have withdrawn the tests

Question 10

What is Classic Galactosaemia (GALT Deficiency)?

Answer 10

• Autosomal Recessive condition
• Leads to severe liver and renal disease which develop at a few days of life. Can cause hypoglycaemia rarely
• Can also cause progressive neurological disease possibly due to Gal-1-P and galactitol
• Cataracts caused by increased galactitol in lens
• Withdrawal of lactose improves Symptoms. If left untreated, can cause sepsis (E.Coli), death

Question 11

What are the enzymes affects in Classic Galactosaemia?

Answer 11

Affects

• Glucokinase
• Galactose-1-Phosphate Uridyl Transferase
• UDP-Epimerase

Question 12

What is the biochemistry of Classical Galactosaemia?

Answer 12

• Elevated liver enzymes
• Jaundice (unconjugated or mixed)
• Abnormal Clotting
• Amino Acids (Tyrosine, Phenylalanine, Methionine)
• Renal Tubular Disease (Acidosis, Amino aciduria)

Question 13

What are diagnostic tests for Galactosaemia?

Answer 13

• Urine tests for galactose (Dipstick, Benedict’s reducing substances)
• Urine sugar chromatography
• Beutler test (qualitative GALT activity in erythrocytes)
• Urine galactitol

Question 14

Which tests have been withdrawn in most centres?

Answer 14

Urine tests for galactose (Dipstick, Benedict’s reducing substances)

• Dip-stick tests detect glucose (may be positive in galactosaemia)
• Benedict’s is non-specific
• Relies on dietary intake
• Technical difficulties (IQC, EQA, UKAS)

Urine Sugar Chromatography

• Relies on dietary intake
• Time taken for assay
• Subjective
• Technical difficulties

Question 15

What are limitations of the Beutler test for analysis for Gal-1-PUT?

Answer 15

False Positive

• K-EDTA anticoagulant
• Delayed analysis
• Glucose-6-phosphate dehydrogenase deficiency can also be picked up

False Negative

• Transfused red blood cells
• Variant alleles

Question 16

What are the features of Urine Galactitol?

Answer 16

Benefits

• Useful if patient transfused
• Also detects galactokinase deficiency

Limitations

• GC-MS so unsuitable for rapid screen

Question 17

What are features of the newborn screening of Galactosaemia?

Answer 17

Included in Irish NBS programme but not recommended by UK National

• Analysis of Galactose and Gal-1-P
• GALT enzyme activity second line test

Question 18

What are limitations of screening for Galactosaemia?

Answer 18

• Does not prevent long-term problems caused by galactosaemia
• Identifies mild variants
• Many cases present before screening result is available

Question 19

How does Galactosaemia get picked up by the UK newborn screening?

Answer 19

Galactosaemia leads to ↑phenylalanine,↑tyrosine, and ↑methionine so inadvertently detected by newborn screening

• Phe/Tyr ratio <1 show no PKU
• ↑phenylalanine, ↑tyrosine, ↑methionine suggest liver disease
• No increase in succinylacetone which means no Tyrosinaemia type 1

Question 20

What is the treatment for Galactosaemia?

Answer 20

• Life-long dietary restriction of galactose
• Avoid all animal milk and breast milk
• Avoid milk in processed foods
• Some hard cheeses are low in galactose
• Non-dairy galactose ?significance
• < endogenously produced galactose

Question 21

What are the long term outcomes for Galactosaemia?

Answer 21

Low lactose/galactose feed leads to resolution of acute neonatal symptoms. Less success with long-term outcome

Cognitive impairment

• Low IQ
• Abnormalities on brain MRI

Bone health

• Nutritional deficiency
• Low bone mineral density

Gonadal impairment

• Primary ovarian insufficiency
• Sub-fertility in males and females – HRT given

Question 22

What are the non classical Galactosaemias?

Answer 22

• Mild GALT deficiency
• Galactokinase deficiency
• Uridine diphosphate galactose 4’-epimerase deficiency (GALE)

Question 23

What are features of mild GALT Deficiency?

Answer 23

• Duarte mutation
• Identified by borderline Beutler test and mutation analysis
• Urine galactitol
• Detected in some NBS programmes or incidentally
• Mild phenotoype, may be asymptomatic
• Benefit of galactose restriction unclear

Question 24

What are features of Galactokinase deficiency?

Answer 24

* Clinically well in neonatal period * Cataracts * Most patients have no other features * Some cases with long-term complications * GALT (Beutler test) is normal * Urine galactitol used

Question 25

What are features of Uridine diphosphate galactose 4’-epimerase deficiency (GALE)?

Answer 25

* Benign to severe neonatal disease * Improve on low galactose/lactose feed * ↑Gal-1-P on some NBS programmes * RBC GALE activity * Gene mutation analysis

Question 26

What are causes of Hereditary Fructose Intolerance?

Answer 26

* Aldolase B deficiency * Fructose-1,6-bisphosphatase deficiency

Question 27

What are symptoms of Aldolase B deficiency?

Answer 27

* GI pain * Vomiting * If untreated, progresses to Lethargy, Coma, Convulsions

Question 28

What is the biochemistry of Aldolase B deficiency?

Answer 28

* Abnormal LFTs * Renal tubular dysfunction

Question 29

What are investigations for Aldolase B deficiency?

Answer 29

* Based on clinical and nutritional history. Onset of symptoms with weaning * Genetics testing mainly * Fructose tolerance test

Question 30

What is the treatment for Aldolase B deficiency?

Answer 30

Resolution with withdrawal of fructose. Children avoid fructose-containing foods (‘neurotic’)

Question 31

How are results intepreted for the Fructose Intolerance test?

Answer 31

* Normal Enzyme Activity: ↑ Glucose and PO4 * Impaired aldolase: ↓ Glucose and PO4

Question 32

What is the GLUT-1 channel?

Answer 32

GLUT1 facilitates transport of glucose across blood brain barrier

Question 33

What is the biochemistry of Fructose-1,6-bisphosphatse deficiency?

Answer 33

* Decreased Gluconeogenesis * Increased NADH/NAD * Increase Lactate * Increased Glycerol * Decreased glucose when fasting or glycogen stores or low (neonates)

Question 34

What is the treatment for Fructose-1,6-bisphosphatse deficiency?

Answer 34

* Avoid Fasting particularly during illness * Regular carbohydrate feeds

Question 35

What can deficiency in GLUT1 lead to ?

Answer 35

* Severe epilepsy * Complex movement disorder * Developmental delay * Milder variants have movement disorder or late-onset epilepsy

Question 36

How is diagnosis of Glucose transporter-1 deficiency made?

Answer 36

* Low CSF/blood glucose ratio. Can also be meningitis so check CSF cell count * Genetic confirmation required

Question 37

What is the treatment of Glucose transporter-1 deficiency?

Answer 37

**Ketogenic diet** * Ketones cross BBB acting as an alternative fuel