1. Galactosemia

2. Galactose Six carbon aldose carbohydrate
Major dietary source is lactose
from milk and milk products
Epimer of glucose
Differs from glucose at carbon 4
Lactose

3. Galactose Metabolism
Patients with galactosemia lack activity of uridyltransferase

4. Clinical Features Failure to Thrive Vomiting Diarrhea Jaundice
Short Term (within 1-2 days after birth)
Failure to Thrive
Vomiting
Diarrhea
Jaundice
Cataracts
Infection and Sepsis
POTENTIALLY LETHAL IF UNDIAGNOSED/UNTREATED

5. Inheritance 1 in ~40,000 live births (7-8K patients in US)
The gene for GALT is located on chromosome 9p13
Classic galactosemia and the other disorders of galactose metabolism are all transmitted by autosomal recessive inheritance and the vast majority of patients are compound heterozygotes

6. Cause of Symptoms? aldose reductase??
Buildup of galactitol causes ????
Mental retardation
Cataracts
Buildup of galactose-1-phosphate ????
Liver and renal damage
Severe mental retardation
Aldose
Reductase
Galactose
Galactitol
NADPH + H+
NADP+

7. The GALT Gene Located at 9p13 4.3 kb in DNA length 11 exons
379 amino acids

8. Missense mutations within the GALT gene
S135L = Leu for Ser
Almost exclusively in individuals of African decent
50% of African American mutations
Q188R = Arg for Gln
Classic galactosemia
60-70% of mutated chromosomes  5  6
K285N = Asn for Lys
2nd most common disease-causing mutation  9
N314D = Asp for Asn
Duarte alleles
2 variations: D1 & D2  10

9. Q188R Most deleterious mutation on GALT gene
Ireland and British (highest frequency)
Close proximity to His-186, the putative catalytic site
Homozygous individuals
show no activity (in vitro)

10. Etiology GALT Mutations: 61% missense mutations
10% small deletions or insertions
9% non-sense mutations (towards C-term)
5% splice-site mutations

11. Diagnosis Newborn screening 48 states including Florida Assays either:
detects level of blood galactose or
measures GALT activity

12. Diagnosis
If you have the misfortune of being born in Washington or Louisiana…
Present with symptoms
Test for reducing substance in urine
Confirm via enzymatic assay

13. Dietary Management Initial management that continues throughout life
Eliminate galactose from the diet
Lactose*
Galactose*
Life-long diet
Calcium supplements
Avoid some pharmaceuticals
Endogenous galactose
Vitamin K
JH Walter, JE Collins & JV Leonard, 1999.

14. Low Galactose Food Pattern
Food Group
Allowed
Not Allowed
Milk & Milk Substitutes
Soy or MCT Formula: Isomil, Nutramigen, Prosobee, Pregsestimil
Breast Milk, Animal Milk, Cheeses, Butter, Ice Cream, Yogurt
Fruits
Most Frozen, Fresh, Canned & Dried*
Dates, Papaya, Persimmon, Watermelon
Vegetables
Most Frozen, Fresh, Canned, & Dried*
Bell Peppers, Tomatoes
Meats & Meat Substitutes
Beef, Poultry, Lamb, Ham Pork, Fish, Game, Kosher Franks, Eggs, Nuts
None*
Breads
Rice, Pasta, Cereals, Breads
Fats
Oil, Lard, Shortening, Mayonnaise
Butter, some margarines
LK Mahan & S Escott-Stump, 1996.

15. male gonad not affected
Clinical Features
Long Term (puberty)
Manifestations
Notes
amenorrhea
male gonad not affected
ovary failure
language problems
mental retardation
especially females

16. Long Term Management Outpatient review throughout life
Dietary compliance
Growth
Biochemical Analysis
Red Cell Galactose-1-Phosphate
Urinary Galactitol
Development
Speech
Cognition
Motor skills
Opthalmology
JH Walter, et al., 1999.

17. An attempt to begin building genotype/
phenotype correlations for various GALT
missense mutations in the hopes of
identifying predictive factors for outcome

18. Background

19. Steady-State Levels
0.2X

20. Activity Wild Type 100± 6 N314D 103 ± 33 E291K 63 ± 10 R201H 63 ± 10
P183T ± 7
T350A ± 1
Y323D ± 1
V151A 5 ± 1
S135L ± .4
R67C ± .4
L139P ± .6
F171S <0.2
Q188R <0.2
R231H <0.2
R259W <0.2
K285N <0.2
R333W <0.2

21. Growth in Glycerol/Ethanol with 0.05% Gal
All strains grew equally well in Glc
Growth in Gal Correlates Well With Activity!!

22. Gal-1-P Accumulation >Gal-1-P correlates with < Activity,
Note lag in intermediate growth correlates
With presence of gal-1-p

23. UDP-Gal is Depleted in Nulls
Arrow Indicates Addition of Gal
Open circle with Gal
Black circle w/out Gal
UDP-Gal levels are depleted in
Nulls (this is true for yeast and
humans but NOT mice???)

24. Conclusions
Enzy Act Negatively Correlates with growth in low gal and gal-1-p accumulation
Depletion of UDP-Gal in the presence of gal in Nulls (same as humans but NOT mice--see next paper)--how?
How do Gal-1-P levels go back down in nulls?

25. Goal: To generate a mouse-KO of GALT in
Order to study galactosemia

26. Successful KO (Mendelian #s)
No GALT Act and Mice
Accumulate Gal-1-P

27. So Far So Good Nulls have elevated gal, galactitol, gal-1-P
(later studies show normal UDP-Gal in KO)

28. Uh Oh Develop to breeding age fine! Females are fertile!
No cataracts, no liver damage, no phenotype!!!

29. What? How toxic is gal-1-p? Is UDP-Gal depletion the culprit?
What about pyrophosphorylase activity?
Aldose Reductase Activity (human>>>mouse)
-is galactitol culprit?
Examples of other diseases which often time biochemically reproduce but do not “clinically” reproduce phenotype
Tay-Sachs, Glycogen Storage Disease TypeII, Lowe and Lesch-Nyhan Syndromes, X-linked adrenoleukodystrophy, alpha-galactosidase deficiency (Fabry disease), and metachromatic leukodystrophy