disorders of amino acid metabolism
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this video explains disorders of
this video explains disorders of amino acid metabolism which include phenylketonuria, alkaptonuria, albinism, and tyrosinemia.
PHENYLKETONURIA (PKU)
i. Deficiency of phenylalanine hydroxylase is the cause of this disease. It is a recessive condition.
ii. The child is mentally retarded with an IQ in the range of 25–50. About 20% of inmates of lunatic asylum may have PKU.
iii. Agitation, hyperactivity, tremors, and convulsions are often manifested.
Laboratory Diagnosis
i. Blood phenylalanine level is drastically increased.
ii. Ferric chloride test: Phenylketone (phenylpyruvate), phenyl lactate, and phenylacetate are excreted in the urine. This could be detected by adding a drop of ferric chloride to the urine. A transient blue-green color is a positive test.
Treatment of Phenylketonuria
i. Early detection is very important. About 5 units of IQ are lost for each 10-week delay in starting the treatment.
ii. The treatment is to provide a diet containing low phenylalanine. Food-based on tapioca (cassava) will have low phenylalanine content.
iii. This special diet is to be continued till 5 years of age; by which time brain development is completed. After that, the child can have a normal diet.
ALKAPTONURIA
Alkaptonuria is an autosomal recessive condition. The metabolic defect is the deficiency of homogentisate oxidase. This results in the excretion of homogentisic acid in urine. There is no mental retardation.
Diagnosis: Urine becomes black on standing when it becomes alkaline. The homogentisic acid is oxidized to black-colored alcapton bodies. Ferric chloride test will be positive for urine.
Benedict's test is strongly positive. Therefore, alkaptonuria comes under the differential diagnosis of reducing substances in the urine.
ALBINISM
1. The Greek word, albino means white. Albinism is an autosomal recessive disease with an incidence of 1 in 20,000 population.
2. Tyrosinase is completely absent, leading to defective synthesis of melanin.
3. The ocular fundus is hypopigmented and the iris may be grey or red. There will be associated photophobia, nystagmus, and decreased visual acuity.
4. The skin has low pigmentation, and so skin is sensitive to UV rays. The skin may show the presence of naevi and melanomas. Hair is also white.
5. Manifestations are less severe in tyrosinase positive type, where the abnormality is in the uptake of tyrosine by melanocytes.
6. Albinism may be produced by the following causes
a) Melanocyte deficiency secondary to a failure of melanoblasts to colonize the skin.
b) Failure of melanocytes to form melanosomes.
c) Due to tyrosinase deficiency, melanin is not produced in the melanosomes.
d) Failure of melanosomes to form melanin owing to substrate deficiency.
e) Failure of melanosomes to store melanin or to transport melanin to keratinocytes.
f) Excessive destruction of functional melanosomes
Tyrosinemia (Type I)
i. It is also called tyrosinosis. It is an autosomal recessive condition with an incidence of 1.5 per 1,000 births. It is due to a deficiency of the enzyme fumaryl acetoacetate hydrolase.
ii. Symptoms manifest by the first 6 months of life and death occurs rapidly. Cabbage-like odor and hypo- glycemia and eventual liver failure are seen. There may be mild mental retardation.
iii. Urine contains tyrosine, para hydroxy phenyl pyruvic acid (p-HPPA), and hydroxyphenyl lactic acid; and serum shows tyrosine.
iv. Tyrosine and phenylalanine restricted diet is advised.
Tyrosinemia (Type II)
It is also known as Richner-Hanhart syndrome. It is due to a deficiency of tyrosine aminotransferase (tyrosine transaminase). Mental retardation, keratosis of the palmar surface, painful corneal lesions, and photophobia are seen. There is increased excretion of tyrosine and tyramine in urine. A diet low in protein is advised.
Neonatal Tyrosinemia
This is due to the absence of the enzyme para hydroxy phenylpyruvate hydroxylase. This deficiency may cause transient hypertyrosinemia in the newborn; this will respond to the administration of ascorbic acid and dietary protein restriction.
#biochemistry#phenylketonuria#alkpatonuria#albinism#tyrosinemia
check out study material here
https://chem4students.blogspot.com/?m=1
PHENYLKETONURIA (PKU)
i. Deficiency of phenylalanine hydroxylase is the cause of this disease. It is a recessive condition.
ii. The child is mentally retarded with an IQ in the range of 25–50. About 20% of inmates of lunatic asylum may have PKU.
iii. Agitation, hyperactivity, tremors, and convulsions are often manifested.
Laboratory Diagnosis
i. Blood phenylalanine level is drastically increased.
ii. Ferric chloride test: Phenylketone (phenylpyruvate), phenyl lactate, and phenylacetate are excreted in the urine. This could be detected by adding a drop of ferric chloride to the urine. A transient blue-green color is a positive test.
Treatment of Phenylketonuria
i. Early detection is very important. About 5 units of IQ are lost for each 10-week delay in starting the treatment.
ii. The treatment is to provide a diet containing low phenylalanine. Food-based on tapioca (cassava) will have low phenylalanine content.
iii. This special diet is to be continued till 5 years of age; by which time brain development is completed. After that, the child can have a normal diet.
ALKAPTONURIA
Alkaptonuria is an autosomal recessive condition. The metabolic defect is the deficiency of homogentisate oxidase. This results in the excretion of homogentisic acid in urine. There is no mental retardation.
Diagnosis: Urine becomes black on standing when it becomes alkaline. The homogentisic acid is oxidized to black-colored alcapton bodies. Ferric chloride test will be positive for urine.
Benedict's test is strongly positive. Therefore, alkaptonuria comes under the differential diagnosis of reducing substances in the urine.
ALBINISM
1. The Greek word, albino means white. Albinism is an autosomal recessive disease with an incidence of 1 in 20,000 population.
2. Tyrosinase is completely absent, leading to defective synthesis of melanin.
3. The ocular fundus is hypopigmented and the iris may be grey or red. There will be associated photophobia, nystagmus, and decreased visual acuity.
4. The skin has low pigmentation, and so skin is sensitive to UV rays. The skin may show the presence of naevi and melanomas. Hair is also white.
5. Manifestations are less severe in tyrosinase positive type, where the abnormality is in the uptake of tyrosine by melanocytes.
6. Albinism may be produced by the following causes
a) Melanocyte deficiency secondary to a failure of melanoblasts to colonize the skin.
b) Failure of melanocytes to form melanosomes.
c) Due to tyrosinase deficiency, melanin is not produced in the melanosomes.
d) Failure of melanosomes to form melanin owing to substrate deficiency.
e) Failure of melanosomes to store melanin or to transport melanin to keratinocytes.
f) Excessive destruction of functional melanosomes
Tyrosinemia (Type I)
i. It is also called tyrosinosis. It is an autosomal recessive condition with an incidence of 1.5 per 1,000 births. It is due to a deficiency of the enzyme fumaryl acetoacetate hydrolase.
ii. Symptoms manifest by the first 6 months of life and death occurs rapidly. Cabbage-like odor and hypo- glycemia and eventual liver failure are seen. There may be mild mental retardation.
iii. Urine contains tyrosine, para hydroxy phenyl pyruvic acid (p-HPPA), and hydroxyphenyl lactic acid; and serum shows tyrosine.
iv. Tyrosine and phenylalanine restricted diet is advised.
Tyrosinemia (Type II)
It is also known as Richner-Hanhart syndrome. It is due to a deficiency of tyrosine aminotransferase (tyrosine transaminase). Mental retardation, keratosis of the palmar surface, painful corneal lesions, and photophobia are seen. There is increased excretion of tyrosine and tyramine in urine. A diet low in protein is advised.
Neonatal Tyrosinemia
This is due to the absence of the enzyme para hydroxy phenylpyruvate hydroxylase. This deficiency may cause transient hypertyrosinemia in the newborn; this will respond to the administration of ascorbic acid and dietary protein restriction.
#biochemistry#phenylketonuria#alkpatonuria#albinism#tyrosinemia
check out study material here
https://chem4students.blogspot.com/?m=1
3 سال پیش
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