Question

Simon and Adrienne are healthy people who lived in a rural area with poor health services when they had their first child, Benjie. He had seizures in infancy, and as he grew into toddlerhood it became apparent that he was severely mentally retarded. He died at 26 months of age. Because he had never been diagnosed with a specific disorder, an autopsy was performed. His brain showed signs of great derangement, with nerve cells degenerating and missing. No diagnosis was made, and because no other relatives had been affected, a genetic problem was not suspected. The family physician assured the couple that the condition was not likely to repeat. The couple waited a few years, then had another child after moving to Chicago. When little Julie had the same symptoms as her brother, Simon and Adrienne took her to a major medical center. Urine and cerebrospinal fluid tests revealed large amounts of the chemical carnosine, which consists of two types of amino acids, alanine and histidine, joined together. Digestion should have broken the carnosine down into the individual amino acids, which are small enough to enter the bloodstream. When a medical geneticist learned of Julie's test results, she tested the urine of the parents. Each had half the normal activity for an enzyme called carnosinase. Julie has, and Benjie had, an inherited disorder, carnosinemia.

1. The mode of inheritance for carnosinemia in this family is __________ .

2. What is the biochemical evidence that indicates the mode of inheritance?

3. The probability that Simon and Adrienne can conceive a child who does not inherit carnosinemia is ____

4. The probability that they can conceive a child who is a carrier like they are is_____.

5. Devise a treatment for carnosinemia. 6. In one experiment on two children with carnosinemia, all sources of dietary protein with an alanine next to a histidine were eliminated from the diet. The children still excreted carnosine in the urine. What is an explanation for this finding?

Answer 1

1. Autosomal recessive

Carnosinemia is having an autosomal recessive mode of inheritance. Recessive gene has to be inherited from both the parent to exhibit the disease.

2. While testing both parent half the normal activity of enzyme carnosine. Parents apperas normal but they are affected hence carriers. Each carry one defective and one normal  gene. Disease which skip generation is said to be recessive type of inheritance,  And both child irrespective of sex is affected which is suggestive of it is not an sex linked inheritance.

3.   

Genotype parent :Cc X Cc (Heterozygous individual because both are carriers)

Poossible Gamete : (C) (c) (C) (c)

Possible Genotype of child

	C	c
C	CC	Cc
c	Cc	cc

CC : Normal :1/4 chances for the child to be normal in each birth

Cc: Carrier 1/2 chances for the child to be carrier in each birth

cc: Diseased 1/4 chances for the child to be diseased in each birth

Probability of Child to be normal :25%

Probability of Child to be Carrier : 50%

Probability of Child to be affected :25%

Question 4

And: 50%

Question 5

Carnosinemia

It is a inherited disorder. Defect in the enzyme Carnosinase responsible for the degradtion the carnsoine. Carnosine is an antioxidant.It is essential for the proper grpwth and development.  Due to lack of enzyme it get accumulated in the urine and CSF. It causes denegeration of the neurons.

No specific treatment developed

Restriction of the diet, reduce red meat which contain high level of carnosine.

Question 6

Ans: Carnosine is a dipeptide compound made by the combination of beta alanine and histamine. It is present in high amount in meat and abscent in the plant products. It is a non essentail compund as it can be synthesized in the body with the help of alanine and histamine. Alanine is an non essential amino acid. A strict diet can only reduce the symptom but not cure carnosinemia. Carnosine enzyme split the carnosine into beta alanine and histidine in the absence of enzyme carnosine will be present in the urine.