🔗 Multiple Endocrine Neoplasia
MEN 1, MEN 2A, MEN 2B — genetics, clinical patterns, surgical protocols, and exam-favourite rules — MRCS high-yield.
Overview of MEN Syndromes
Multiple Endocrine Neoplasia (MEN) syndromes are rare, autosomal dominant inherited disorders characterised by the development of hyperplastic and neoplastic lesions in two or more endocrine glands. Each type has a characteristic combination of affected glands, a specific genetic mutation, and critically distinct surgical management rules.
MEN 1
Werner Syndrome
MEN1 gene · Chromosome 11 · Menin protein
The “3 P’s”
- 95% Parathyroid hyperplasia → Primary HPT, hypercalcaemia
- 70% Pituitary adenoma (prolactinoma most common)
- 50% Pancreatic/duodenal endocrine tumours (gastrinoma, insulinoma)
Autosomal dominant · tumour suppressor gene (loss of function)
MEN 2A
Sipple Syndrome
RET proto-oncogene · Chromosome 10 · gain-of-function
2 P’s and 1 M
- ~100% Medullary Thyroid Carcinoma (MTC) → calcitonin
- 50% Phaeochromocytoma → catecholamines
- 5–20% Parathyroid hyperplasia → hypercalcaemia
Autosomal dominant · RET gain-of-function oncogene
MEN 2B
Most Aggressive
RET proto-oncogene · Codon 918 · gain-of-function
1 P and 2 M’s
- ~100% Medullary Thyroid Carcinoma — most aggressive variant
- 50% Phaeochromocytoma
- ~100% Marfanoid habitus + Mucosal neuromas — lips, tongue, GI tract
- ⚠️ No parathyroid involvement
Autosomal dominant · RET codon 918 · most aggressive MTC
At-a-Glance Comparison
| Feature | MEN 1 | MEN 2A | MEN 2B |
|---|---|---|---|
| Gene | MEN1 (chr 11) — Menin | RET (chr 10) — codon 634 most common | RET (chr 10) — codon 918 |
| Type | Tumour suppressor (loss of function) | Proto-oncogene (gain of function) | Proto-oncogene (gain of function) |
| Parathyroid | ✅ 95% — 4-gland hyperplasia | ✅ 5–20% — hyperplasia | ❌ Not affected |
| Pancreas / gut | ✅ 50% — gastrinoma, insulinoma | ❌ | ❌ |
| Pituitary | ✅ 70% — prolactinoma most common | ❌ | ❌ |
| MTC | ❌ | ✅ ~100% | ✅ ~100% — most aggressive |
| Phaeochromocytoma | ❌ | ✅ ~50% | ✅ ~50% |
| Marfanoid / neuromas | ❌ | ❌ | ✅ — pathognomonic |
| Prophylactic thyroidectomy | Not applicable | Yes — by age 5 typically | Yes — in infancy (<6 months) |
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