HPTA refers to hypothalamic-pituitary-thyroid axis. HPGA refers to hypothamalic-pituitary-gonadal axis. Any other use is incorrect, and I don't care how many initials the person has after their name. It's a common mistake, generally made by those outside of the field of endocrinology, but a mistake nevertheless.
HPG-axis hormones during puberty: a study on the association with hypothalamic and pituitary volumes.
Psychoneuroendocrinology. 2010 Jan;35(1):133-40. doi: 10.1016/j.psyneuen.2009.05.025.
Molecular regulation of hypothalamus-pituitary-gonads axis in males.
Gene. 2014 Nov 1;551(1):15-25. doi: 10.1016/j.gene.2014.08.048. Epub 2014 Aug 26.
Hypothalamic-pituitary-gonadal axis in two men with aromatase deficiency: evidence that circulating estrogens are required at the hypothalamic level for the integrity of gonadotropin negative feedback.
Eur J Endocrinol. 2006 Oct;155(4):513-22.