5a-Reductase catalyzes the metabolism of testosterone to DHT.

Individuals with 5a-reductase deficiency exhibit decreased concentrations of DHT and impaired virilization of the male urogenital tract.

Individuals with 5a-reductase deficiency appear phenotypically female externally or may have ambiguous external genitalia, with normal male internal genitalia.

(E) alpha-Iduronidase (correct)

The only lysosomal storage disease that presents with corneal clouding (as far as I know) is Hurler's syndrome, which is one of two mucopolysaccharidoses, the other being Hunter syndrome. Hunter syndrome can be distinguished from Hurler syndrome in that Hunter syndrome does not present with corneal clouding (Hunters see clearly [no corneal clouding] and aggressively aim for the X [X-linked recessive]). Hurler's syndrome is due to a deficiency in alpha-L-Iduronidase, and Hunter syndrome is due to a deficiency in Iduronate-2-sulfatase. Both diseases lead to an accumulation of heparan and dermatan sulfate.

(C) Cryptosporidium parvum (correct) vs (E) Giardia lamblia (incorrect)

There are three main protozoa that cause GI infections:

• Giardia lamblia - which causes fatty, foul-smelling stools, is transmitted via cysts in water (usually unfiltered river or lake water), and on histology, shows a flagellated, pear-shaped trophozoite with two large, central nuclei
• Entamoeba histolytica - which causes bloody diarrhea or dysentery, liver abscesses, RUQ pain, and presents with flask-shaped ulcers on colon biopsy
• Cryptosporidium - which causes watery diarrhea in immunocompetent hosts and severe diarrhea in AIDS patients, transmits via oocysts in water, and is an AIDS-defining illness (happens at CD4+ < 100/mm3)

(F) Pleural effusion (correct)

Pleural effusion presents with

• decreased breath sounds (fluid in the pleural cavity dampens the transmission of sound and mechanical waves)
• dullness to percussion
• decreased tactile fremitus

Note that in pleural effusion, these tests are all "dulled" or are all "decreased".

Pneumothorax presents with

• decreased breath sounds
• hyperresonance to percussion
• decreased tactile fremitus

all on the affected side.

Lobar pneumonia (or a consolidated lung) presents with

• decreased breath sounds
• dullness to percussion
• increased tactile fremitus because the consolidated lung is adjacent to the body wall