Mystery osteoporosis causes 30female

Diagnosed with osteoporosis early 30s with no risk factors or family history. Rheumy are doing a tonne of investigations but so far all normal, minus low phosphate for the last 4 years (mild-moderate) and low urea (again for many years).

Got a urine sample and repeat fasted phosphate bloods to do, along with some extras thrown in, to check for kidney wasting conditions. Looked up all the conditions I could find and none seem to fit. Understanding low phosphate can lead to osteomalacia not osteoporosis.

Genetic testing will be the next step, but again, none seem to fit from what I can see.

What other conditions can cause this at such a young age? I am active, do impact activities, eat well, been sporty my whole life, everything else is in range, no family history. Got hypermobile Ehlers Danlos and POTS.

Phosphate been 0.6-0.75 last 4 years

Vitamin D was previously classed as just low but now apparently the boundaries have moved so it's been normal 50-70ish

Urea often 1.4ish