Parents Were Concerned About Their 16-year-old Son For The Following

Parents were concerned about their 16-year-old son for the following reasons: he had no deepening of his voice, scanty pubic and axillary hair growth, absence of beard and mustache growth, small penis, poor muscular development, and psychosocial immaturity.
Laboratory evaluation indicated the following:

Serum testosterone
100 ng/dL
Sperm count
10 million/mL semen
The following tests were performed:

Clomiphene (a nonsteroidal, weak estrogen agonist that stimulates the release of gonadotropins) 100 mg/day for seven days: 0% increase in LH (50% is normal)

Gn-RH (100 µg I.V.): 0% increase in LH in twenty minutes (300% is normal)

HCG (5000 I.U., I.V.): 50% increase in plasma testosterone one to three days after injection

This person was subsequently treated with FSH at 25-75 U three times/week and HCG as described above. Sperm count and testosterone levels were both near normal after two months of treatment, and primary and secondary sex characteristics appeared.

What is the endocrine disorder in this individual?
2. Is this a primary or secondary disorder? Why?
3. Why is HCG used in the treatment?
4. Both FSH and HCG are needed in the treatment. Explain Why