IGS is not Pernicious Anemia.

Most people who've heard of B12 deficiency know about Pernicious Anemia (PA). They're not the same condition. Here's how they differ:

Pernicious Anemia:

• Autoimmune—your immune system attacks the cells that make intrinsic factor

• Develops later in life (typically 40s-60s)

• You were healthy before it started

• Your nervous system developed normally

• Diagnosis: intrinsic factor antibodies or parietal cell antibodies

Imerslund-Gräsbeck Syndrome (IGS):

• Genetic—you're born with a non-functional B12 receptor

• Present from birth

• You were never able to absorb B12

• Your nervous system may have never been fully built

• Diagnosis: genetic testing (CUBN or AMN gene mutations)

Why this matters:

Someone with PA was healthy for 40-50 years before their absorption failed. Their brain developed normally. Their nervous system was fully built. Treatment is restoring what they had.

Someone with IGS was depleted from the start. Their brain developed without adequate B12. Their myelin may have never been properly formed. Damage accumulates silently from infancy—often for decades before anyone thinks to check.

Same vitamin. Same injections. Very different disease. Very different timeline. Very different level of damage by the time it's caught.

If you were diagnosed with PA but your symptoms started in childhood—or if your B12 was deficient from your very first test—IGS may be what you actually have.