It is 1 disease, but it has a spectrum of severity.
Until recently, PBD-ZSD was viewed as 3 separate diseases, but we now know it is a set of disorders that form a spectrum, or continuum, of 1 disease. This spectrum can range from mild (infantile Refsum disease, or IRD), to moderate (neonatal adrenoleukodystrophy, or NALD), to severe (Zellweger syndrome, or ZS).

It is 1 disease, but it has a spectrum of severity.
Until recently, PBD-ZSD was viewed as 3 separate diseases, but we now know it is a set of disorders that form a spectrum, or continuum, of 1 disease. This spectrum can range from mild (infantile Refsum disease, or IRD), to moderate (neonatal adrenoleukodystrophy, or NALD), to severe (Zellweger syndrome, or ZS).

It is 1 disease, but it has a spectrum of severity.
Until recently, PBD-ZSD was viewed as 3 separate diseases, but we now know it is a set of disorders that form a spectrum, or continuum, of 1 disease. This spectrum can range from mild (infantile Refsum disease, or IRD), to moderate (neonatal adrenoleukodystrophy, or NALD), to severe (Zellweger syndrome, or ZS).