Which of the following statements is true regarding autosomal recessive inheritance?
Correct Answer D:
Autosomal recessive:
In autosomal recessive inheritance:
If two heterozygote parents:
Autosomal recessive disorders are often metabolic in nature and are generally more life-threatening compared to autosomal dominant conditions.
What chromosome abnormality is associated with Klinefelter's syndrome?
Correct Answer B:
Klinefelter's syndrome:
Klinefelter's syndrome is associated with karyotype 47, XXY
Features:
Diagnosis is by chromosomal analysis
A rapid urine screening test is developed to detect Chlamydia. A trial involving 200 men and women is performed comparing the new test to the existing NAAT techniques:
What is the negative predictive value of the new test?
Correct Answer A: Negative predictive value = TN / (TN + FN) = 172 / (172 + 5)
Screening test statistics:
It would be unusual for a medical exam not to feature a question based around screening test statistics. The available data should be used to construct a contingency table as below:
TP = true positive; FP = false positive; TN = true negative; FN = false negative
The table below lists the main statistical terms used in relation to screening tests:
Positive and negative predictive values are prevalence dependent. Likelihood ratios are not prevalence dependent.
An 18-year-old male presents is reviewed in the endocrinology clinic due to concerns about delayed pubertal development, despite being 1.77m tall. On examination he has scant pubic hair and reduced testicular volume. The following blood results are obtained:
What is the most likely diagnosis?
Correct Answer E: Klinefelter's - LH & FSH raised.
Kallman's - LH & FSH low-normal.
Kallman's syndrome is a recognized cause of delayed puberty secondary to hypogonadotrophic hypogonadism.
It is usually inherited as an X-linked recessive trait. Kallman's syndrome is thought to be caused by failure of GnRH-secreting neurons to migrate to the hypothalamus.
The clue given in many questions is lack of smell (anosmia) in a boy with delayed puberty.
A 60-year-old man who is currently receiving chemotherapy for non-small cell lung cancer presents for review. He is currently being treated with oral calcium supplements as hypocalcaemia was detected during a recent admission. Bloods taken two days ago reveal the following:
Which one of the following tests may help determine why his calcium level remains low despite calcium supplementation?
Correct Answer E: Cisplatin, often used in the management of non-small cell lung cancer, is a well known cause of magnesium deficiency. Without first correcting magnesium levels it is difficult to reverse hypocalcaemia.
Whilst measuring the parathyroid hormone level is always useful it is likely to be elevated unless the patient has coexistent hypoparathyroidism.
Hypocalcaemia: causes and management: The clinical history combined with parathyroid hormone levels will reveal the cause of hypocalcaemia in the majority of cases.
Causes:
Acute pancreatitis may also cause hypocalcaemia. Contamination of blood samples with EDTA may also give falsely low calcium levels.
Management:
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