text: Yo, listen up, I got a story to tell,
  'Bout a disorder that you know so well.
  X-linked agammaglobulinemia, it's the name,
  A primary immunodeficiency, it's a real pain.
  
  Caused by mutations in the BTK gene,
  On the X chromosome, it's a crazy scene.
  Messing up B-cell development, that's the deal,
  Immunoglobulin levels drop, it's for real.
  
  Infections and neoplasms, they come along,
  XLA patients, they can't be strong.
  Colorectal cancer, a risk they face,
  For occasional cases, it's a real disgrace.
  
  Low levels of B lymphocytes, that's the key,
  Immunoglobulins low, can't you see?
  Congenital immune disorder, it's a tough road,
  Makes 'em more prone to drug-related toxic load.
  
  So before you start chemo, gotta be wise,
  Gene sequencing, monitoring, no compromise.
  Predicting DRT, that's the aim,
  For XLA patients with CRC, it's a whole new game.