Maple Syrup Urine Disease, Phenylketonuria & Alkaptonuria

1. Course Code: GEB204
Course Title: Biochemistry & Molecular Biology of Disease
Presentation on
Maple Syrup Urine Disease, Phenylketonuria & Alkaptonuria
Group Members
Asma Hossain
ID: 2015-2-77-004
Rahatul Kabir
2015-2-77-033
Syeda Kashfia Kabir
2015-2-77-008
Kaberi Mostafa Saathi
2015-2-77-017
Farhana Shikder Lamia
2015-2-77-025
http://www.skara.se/

2. Metabolic Disorder
• A metabolic disorder can happen when abnormal chemical reactions in the body alter
the normal metabolic process.
• It can also be defined as inherited single gene anomaly, most of which are autosomal
recessive.
• Inherited metabolic disorders are one cause of metabolic disorders, and occur when a
defective gene causes an enzyme deficiency. Metabolic diseases can also occur when
the liver or pancreas do not function properly.
• Some metabolic disorders are
Maple syrup urine disease
Phenylketonuria
Alkaptonuria

3. Maple Syrup Urine Disease

4. Introduction
• Maple syrup urine disease (MSUD) is an inherited metabolic disorder. Metabolic
disorder can happen when abnormal chemical reactions in the body alter the
normal metabolic process
• Person who is affected by MSUD is unable to process certain amino acids
properly.
• MSUD is a rare genetic disorder characterized by deficiency of certain enzymes.
• MSUD due to an enzyme defect in the catabolic pathway of the branched chain
amino acids.

5. Inheritance Pattern of MSUD
• MSUD is an autosomal recessive metabolic disorder affecting branched chain amino
acid.
• Develops from inheriting a mutated gene from each parent.
• Mutation in BCKDHA (19q13.1-q13.2), BC2DHB (6p22-p21, 6p14 for Ashkenazi Jews)

6. Molecular mechanism

7. Signs & Symptoms of MSUD
• Symptoms are:-
 Sweet smelling urine and sweat
 Poor feeding
 Loss of appetite
 Weight loss
 Irregular sleep pattern

8. • Babies with MSUD may also have episodes known as a “metabolic
crisis”. Symptoms of a metabolic crisis include:-
 Lack of energy
 Vomiting
 Irritability
 Breathing difficulties

9. Causes of MSUD
• Mutations in the BCKDHA, BCKDHB,
and DBT genes can cause maple syrup
urine disease. This 3 genes make a protein
complex which is essential for breaking
down the branched chain amino acids
leucine, isoleucine, and valine.
• Mutations in any of these three genes
reduce or eliminate the function of the
protein complex, preventing the normal
breakdown of the amino acids.
• Accumulation of these amino acids and
their toxic byproducts results in the serious
health problems associated with MSUD.

10. Risk Factors
• It is reported by National Organization for Rare
Disorders that MSUD occurs at the same rate in
males and females.
• The risk for having any form of MSUD depends
on whether parents are carriers of the disease. If
both parents are carriers, their child has:
I. 25% chance of receiving two mutated genes
which causing MSUD.
II. 50% chance for receiving only one defective
gene and being a carrier.
III. 25%chance of receiving one normal gene from
each parent.

11. Diagnosis
• Physical exam with evaluation of family medical history of the newborn.
• Urine amino acid test.
• Plasma amino acid test: A blood sample drawn from the baby’s heel detects high
leucine levels.
• Urine smell which is like maple syrup.
• Ear wax may be examined sometimes for smell; it is similar to maple syrup smell.

12. Treatment
• High-protein foods need to be limited in diet. Such as:
milk, fish, meat, egg, nuts etc.
• Tracking BCAA levels.
• Thiamine supplement is beneficial for the children who
have “thiamine-responsive MSUD”.
• Liver transplant surgery is an optional treatment for
people with MSUD.
• In the past, dialysis was used to cleanse the body. This is
no longer used.

14. • PKU is an metabolic disorder (inborn error) inherited in
autosomal recessive manner.
• Caused by a defect in the gene that helps create an enzyme that
breaks down phenylalanine.
• Phenylalanine is an essential amino acid in the body.
• Unprocessed phenylalanine builds up toxic levels in the blood
and brain without proper management.
• Very rare, only 1/15000 children in the U.S are born with it.

15.  Mental retardation
 Seizures, shaking, or jerking movements
 Stunted or slow growth
 Skin rashes, like eczema
 Microcephaly
 Mousy odour in urine, breath
 Hypopigmentation or albinism
 Very low IQ

16.  Caused by a mutation in PAH gene
located on the 12th chromosome.
 The mutated PAH gene can reduce the
activity of phenylalanine hydroxylase
enzyme.
 phenylalanine from the diet cannot be
processed effectively.
 phenylalanine can build up to toxic
levels in the blood and other tissues.
 The excessive amounts of this
phenylalanine can cause brain damage
and other developmental problems.

19. Guthrie’s test
•Newborn blood sample
•microorganism Bacillus subtillus
FeCl3 test
•PKU in urine gives a bluish green color when it reacts with FeCl3 .
•This test is not specific.
Prenatal diagnosis
•Requires molecular testing
•CVS
•Amniocentesis

20.  .

21.  We can manage the PKU through the
diet and regular blood testing.
 Foods that are high in protein must be
avoided as all protein contains
phenylalanine.
 Foods containing aspartame should
not be consumed.
 A special metabolic formula that
provides all other vitamins, minerals,
proteins and energy the baby needs to
grow is essential.
 The energy and varieties are provided
by low-protein foods, including fruits,
non-starchy vegetables.

22. ALKAPTONURIA

23. WHAT IS ALKAPTONURIA?
Alkaptonuria (AKU, black urine disease, black bone disease) is
an inborn error of amino acid metabolism: rare disorder of
autosomal recessive inheritance in which the body cannot process
the amino acids phenylalanine and tyrosine , which occur in
protein due to a mutation in a gene.
AFFECTED POPULATIONS:
It affects males and females in equal numbers, although
symptoms tend to develop sooner and become more severe in
males.
In the United States it is estimated to occur in 1 in 250,000-
1,000,000 live births.
Alkaptonuria has been reported in all ethnic groups. Areas with
increased frequencies of the disorder have been identified in
Slovakia, the Dominican Republic and Germany.

24. MOLECULAR MACHANISM
It results from absence of homogentisate 1,2
dioxygenase (HGD) enzyme, predominantly
produced by hepatocytes in the liver and
within the kidney, is responsible for the
breakdown of homogentisic acid (HGA); an
intermediate in the degradation pathway of
the amino acids (phenylalanine and tyrosine)
to the Krebs cycle.

25. MOLECULAR MACHANISM
• It is caused by a mutation or defect in HGD gene.
• Cytogenetic Location: chromosome 3 in region 3q21-q23.
• Molecular Location: base pairs 120,628,168 to 120,682,571
on chromosome 3.
• HGD is split into 14 exons, ranging from 35 to 360 bp in
lengths.
• AKU-causing mutations are distributed throughout the entire
HGD gene with some prevalence in exons 8, 7, 6, 3 and 13.
• Missense mutations are the most numerous, followed by
splicing, frameshift, nonsense, genomic deletions and finally,
one change leading to expansion.
• More than 65 mutations in the HGD gene have been
identified in people with alkaptonuria. Most of these
mutations change single amino acids used to build the
homogentisate oxidase enzyme. For example, a substitution
of the amino acid valine for the amino acid methionine at
protein position 368 is the most common HGD mutation in
European populations.
• Due to this mutation or defect in HGD gene which causes
lack of this enzyme and that results in the accumulation of
HGA.

26. MOLECULAR MACHANISM
HGD protein and effects of the mutations:
• The HGD gene codes for the protomer composed of 445 amino acids.
• The functional, wild-type HGD enzyme is a hexamer (it has six subunits) that are
organized in two groups of three (two trimers) and contains an iron atom.
• Different mutations may affect the structure, function, or solubility of the
enzyme. Some will affect the assembly of the hexamer, others will affect the
stability of the protomer and some will interfere with the active site of the
enzyme.
• Without HGD, the build up of HGA occures in the bones, cartilage and urine.
• In contact with air, HGA reacts with oxygen and turns the urine black. This is
caused by a black pigment called “alkapton”, and leads to the name alkapton-
uria.
• This same black pigment, in a process called ochronosis, causes tissue and bone
to darken and degenerate. This causes painful and disabling joint disease, known
as osteoarthritis.

27. The risk factors of Alkaptonuria include:
• Family history of the condition: Alkaptonuria is a
genetic disorder inherited in an autosomal recessive
pattern. This means that the mutation must be inherited
from both parents in order to inherit the disorder and
manifest the signs and symptoms of Alkaptonuria.
• If the individual only inherits one copy of the mutated
gene, they will be a carrier of AKU and will not
manifest the disorder.

28. Some Symptoms of Alkaptonuria
Dark stains on a baby’s diaper one of the earliest
signs of Alkaptonuria. Symptoms become more
noticeable after ages, such as:
• Dark spots in the sclera of eyes
• Thickened and darkened cartilage in ears
• Blue speckled discoloration of skin, particularly
around sweat glands
• Dark-colored sweat or sweat stains
• Black earwax
• Kidney stones
• Osteoarthritis (especially hip and knee joints)
• Heart problems

29. Diagnosis
• The diagnosis of alkaptonuria is based
on the detection of a significant
amount of HGA in the urine by a test
called gas chromatography.
• DNA testing also used to check for
the mutated HGD gene.
• Family history is very useful in
making a diagnosis of alkaptonuria.
However, many people don’t know
they carry the gene. Their parents
might be carriers without realizing it.

30. Treatments
There is no specific treatment for Alkaptonuria. Main
treatment attempts have focused on preventing ochronosis
through the reduction of accumulating homogentisic acid.
Commonly recommended treatments include:
•Put on a low-protein diet.
•Large doses of Ascorbic acid or vitamin C
•Nitisinone may be effective in the treatment of alkaptonuria.
Nitisinone blocking the production and accumulation of
HGA.
•Doctor may prescribe anti-inflammatory medications or
narcotics for joint pain.
•Physical and occupational therapy may help to maintain
flexibility and strength in muscles and joints.
•Avoid activities that put a lot of strain on joints.
Other treatments for alkaptonuria are focused on
preventing and relieving possible complications, such as:
• Arthritis
• Heart disease
• Kidney stones

31. CONCLUSION
• Although these conditions do not reduce life expectancy, they
significantly affect quality of life.
• There is no proper treatments available to cure these diseases, we
can just prevent and manage these diseases.
• Since, here discussed all diseases are inherited in a autosomal
recessive manner, genetic counseling will help assess risks, before
planning for a child.

32. Thank You!
Any Questions?