Name: Rosie Gilbert

Theme: Enzymology

OPTION LIST

A	galactosidase A	I	porphobilinogen deaminase
B	glucose-6-phosphate	J	lactate dehydrogenase
C	myophosphorylase	K
D	prostate specific antigen	L
E	adenosine deaminase	M
F	alanine aminotransferase	N
G	alkaline phosphatase	O
H	glucagon	P

For each scenario below, choose the most appropriate answer from the list above. Each option may be used once, more than once or not at all.

1. An elderly man turns up at his GP complaining of tiredness and a troublesome back pain. His wife interrupts to say that he keeps getting up during the night to go to the toilet. On further questioning concerning his waterworks, he admits to some difficulty in passing urine and a feeling of incomplete voiding. You order some blood tests. Which enzyme is most likely to be raised?

2. A 3-month-old boy was admitted to hospital with failure to thrive, and a persistent cough. On examination his height and weight were below the third centile. Subsequent immunological investigations have shown marked T- and B-cell lymphopaenia and hypogammaglobulinaemia, suggestive of severe combined immunodeficiency (SCID). This disorder is frequently caused by a deficiency in which enzyme?

3. A worried mother brings her obese 12 year old son to the GP, saying that he avoids exercise and has been recently found to be skipping his PE lessons. When confronted about this, the boy claimed that ‘it hurts when he exercises’. The skeptical GP was about to say ‘no pain, no gain’, when he remembered a lecture in medical school about McArdle’s glycogen storage disease (type V), which causes stiffness following exercise. He referred the boy for a muscle biopsy, which confirmed a deficiency in an enzyme involved in glycogen metabolism. Name this enzyme.

4. A 36 year old pregnant woman presents with abdominal pain in the right upper quadrant. Blood tests reveal elevation of liver enzymes, in a pattern which suggests biliary outflow obstruction. Which enzyme is likely to be the most elevated?

5. A young man presents with a history of recurrent febrile illness associated with painful parasthesiae in his hands and feet. On examination, you notice small red papules clustered in his pelvic and thigh region. Urine dipstick shows protein +++. The patient complains that no doctor has been able to find out what is wrong with him. However, having recently passed your path exam, you suspect he might have Fabry’s disease, an X-linked disorder of glycolipid metabolism due to deficiency of ___?

ANSWERS

1. D

2. E

3. C

4. G

5. A