Genetics, Stats

Question 1

A boy has retinal dystrophy. His father also has it while his mother is healthy. There is no history of consanguinity. His two sisters are healthy.

What mode of inheritance is most likely?
X-linked dominant
autosomal recessive
X-linked recessive
autosomal dominant

Answer 1

This cannot be X-linked recessive because fathers cannot pass this disease to their sons. It is very unlikely to be X-linked dominant because such conditions are extremely rare in clinical practice, and one would expect others in the family to be affected. This leaves autosomal dominant or recessive. A condition occurring in 2 consecutive generations without consanguinity is unlikely to be recessive. Thus autosomal dominant is the most likely here

Question 2

A study compared carotid endarterectomy with medical therapy for stroke prevention over 2 years. 18% of patients in the medical therapy group developed a stroke, compared with 8% in the carotid endarterectomy group.
What is the number needed to treat over 2 years to prevent 1 stroke?
20%
100 / 18
100 /8
100 /(18 - 8)
(18-8) / 100

Answer 2

100 /(18 - 8)

Question 3

A 37-year-old woman develops a left-sided facial weakness. She has impairment of taste in the anterior two thirds of the tongue, and complains that sounds are much louder than usual on that side. There is no disturbance of balance or nystagmus evident. Tear production is normal in both eyes.

Where is the lesion affecting her seventh cranial nerve most likely to be:
at the left stylomastoid foramen
proximal to the left geniculate ganglion
in the left facial canal
at the left cerebellopontine angle
in the left parotid gland

Answer 3

Generally speaking, the more proximal a lesion, the greater the number of functions affected. A distal lesion (outside the stylomastoid foramen) may only affect motor function. Lesions in the facial canal can affect taste to the anterior two thirds of the tongue, more proximally in the canal may produce hyperacusis due to involvement of stapedius muscle. Abnormalities in tear production can occur with lesions of the geniculate ganglion. Cerebellopontine angle lesions usually produce eighth nerve disturbance, in addition.

Question 4

Ocular abnormality most likely seen in Sturge Weber

Answer 4

Sturge-Weber syndrome is characterized by naevus flammeus of the facial skin with angioma of the meninges. It is associated intra-ocularly with:
choroidal haemangioma
glaucoma due to vascular proliferation in the angle

Question 5

Thymus originates from what pharyngeal pouch ?

Answer 5

The thymus is the only option above arising from the third pharyngeal pouch. The tympanic membrane arises from the first pharyngeal pouch. The superior parathyroid gland arises from the fourth pharyngeal pouch. The parafollicular gland arises from the fifth pharyngeal pouch.

Question 6

Recognised complications of YAG capsulotomies include:

Answer 6

Recognised complications of YAG capsulotomies include:
lens pitting
iritis
raised IOP
retinal break
macula oedema