Biology of Disease

15.11 Summary

The sequence of nucleotides of the genes in the DNA forms the genetic
blueprint of cells, controlling all the cell’s activities. This DNA sequence
is transmitted to offspring in the gametes. Alterations in the sequence of
nucleotides or to the chromosomal content of cells, that is, mutations,
can lead to disease and/or death. Mutations may result in absence or
abnormality of a protein, perhaps an enzyme. Chromosomal aberrations
involve structural changes to individual chromosomes, such as deletions,

SUMMARY

CZhhVg6]bZY!BVjgZZc9Vlhdc!8]g^hHb^i]:YLddY ))*

Christine was born after a normal pregnancy. For

the first few days she was healthy but then started to

vomit frequently. Her mother noted that her urine had

a peculiar mousy smell. About a month after birth,

Christine was admitted to hospital for the frequent

vomiting where it was realized that the genetic screening

test after her birth had been deficient. Her blood was

analysed for phenylalanine as shown (reference value

in parentheses).

Plasma [phenylalanine] 1.6 mmol dm–3 (<0.1 mmol

dm–3)

Questions

(a) What is the diagnosis for Christine?

(b) How should Christine be treated?

(c) Why does Christine’s urine have a characteristic

mousy odor?

(d) What would happen to Christine if she were not

treated?

CASE STUDY 15.1

Jane is a 39-year-old healthy woman who has just given

birth to her first child, a son, Peter. She had wanted the

pregnancy in her words ‘to be completely natural’ and

had refused an amniocentesis. Unfortunately, Peter

shows the very obvious physical characteristics of Down

syndrome. Below is Peter’s karyogram.

Questions

(a) Examine the karyogram. What is the cause of Down

syndrome in this case?

(b) Given that a clinical diagnosis of Down syndrome

is nonproblematical, why is it necessary to obtain

a karyotype?

(c) What advice would you give Jane?

CASE STUDY 15.2