14 y.o. with low DLCO and clear CT of Lungs

I noticed my 14 year old daughter getting short of breath about 6 months ago and thought she just needed more exercise although her BMI is 18% and she does go out and play a lot.  However her breathing continued to be a problem so I took her to the doctor.  A PFT was done earlier in January, the results are:

1.  There is a proportionate decrease in FVC and FEV1 with a preserved FEV1/FVC ratio consistent with a Restrictive Lung Defect.      
2.  Reduced total lung capacity measured by Plethysmography suggesting a mild restrictive pattern.    
3.  Elevated residual volume suggests Air Trapping.    
4.  DLCO is Moderately Reduced.

Her adjusted DLCO value was 54% of the predicted value, her TLC was 76%, the FVC was 79%,  and the FEV1 was 81%.  I took her to the ER the other night because she couldn't breath and her chest xray looked okay and the EKG appeared normal.  A CT was done and that came back normal as well.  The only thing noted was a 23 degree thoracic scoliosis which is not causing any of her breathing problems.  Is there something the doctors could be missing that would cause these issues?  

One doctor is suspecting Marfan Syndrome.  She has loose joints, wears bifocals, has an eye tracking problem, has a congenital bladder diverticulum, corrected kidney reflux, an Interstim implant for urinary dysfunction, mild osteopenia and ADD.  Any insight would be wonderful!  Thank you so much!

[zodiacqueen]

Hi, have you looked into pulmonary hypertension and pulmonary embolism?  Pulm emb. will only show up with a CT with contrast?  Pulmonary hypertension, I believe can be tested with a special catheter placed in the pulmonary vessels.  They test the pressures within the lungs.  These 2 are possibilities.  I sure hope the doctors thought of these conditions!

Good luck to you.  I hope you and your daughter find a solution very soon!