Multiple Endocrine Neoplasia Type 1

Multiple Endocrine Neoplasia Type 1
-National Endocrine and Metabolic Diseases Information Service, National Institutes of Health

• An overview of MEN1.

Endoscopic Removal of Pituitary Tumors

Endoscopic transphenoidal resection of pituitary tumors at UCLA.

Drug-resistant hyperprolactinemia

MEN1 frequently involves pituitary disease. One study found pituitary disease occurred in 42% of MEN1 patients.⁽¹⁾ Depending on the specific type of pituitary disorder, treatment may include the surgical removal of an adenoma, the use of hormones or drugs to normalize pituitary function, or radiotherapy.

A prolactinoma, for example, is a non-cancerous pituitary tumor that produces the hormone prolactin; it's the most common form of pituitary tumor.⁽²⁾ Prolactinomas tend to cause hyperprolactinemia, abnormally high blood levels of prolactin. This can cause a variety of symptoms, including interfering with normal ovulatory function in women.

Normally, prolactin-producing cells are down-regulated, or inhibited, by dopamine signals from the hypothalamus.⁽³⁾ Therefore, hyperprolactinemia often is treated by dopamine agonists, usually Cabergoline or Bromocriptine.

Cabergoline usually is more effective than Bromocriptine at normalizing prolactin levels and restoring gonadal function.⁽⁴⁾ Yet it is not always successful in lowering prolactin to normal levels.

One particular patient, "P", was found to have hyperprolactinemia which then prompted an MRI scan and diagnosis of a pituitary adenoma. Treatment with Cabergoline was started. Within four months, the adenoma shrank and was no longer detectable via MRI, and P's prolactin level dropped to normal levels. But not for long. The prolactin level began to rise, and P's doctor responded with increasing dosage of Cabergoline. This went on for eight years, with Caborgoline dosage of up to 2.5mg/wk and prolactin levels typically about 50-100 mg/dL. When Cabergoline was discontinued, the prolactin would shoot up to about 180, and when Cabergoline was resumed, prolactin would reduce but not normalize. Periodic MRIs suggested possible empty sella syndrome and no sign of adenoma.

P's treatment subsequently was switched to Bromocriptine for a year, but her prolactin did not respond as well as it did to Cabergoline, and so Cabergoline was resumed.

What is there to do for a patient whose hyperprolactinemia does not respond sufficiently to dopamine agonist therapy, and who does not exhibit an operable adenoma?
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⁽¹⁾ Bruno Vergès, et al. Pituitary Disease in MEN Type 1 (MEN1): Data from the France-Belgium MEN1 Multicenter Study. The Journal of Clinical Endocrinology & Metabolism February 1, 2002 vol. 87 no. 2, 457-465.
⁽²⁾ http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001377/
⁽³⁾ http://en.wikipedia.org/wiki/Dopamine#Regulating_prolactin_secretion
⁽⁴⁾ Webster, et al. A Comparison of Cabergoline and Bromocriptine in the Treatment of Hyperprolactinemic Amenorrhea. N Engl J Med 1994; 331:904-909

The amino acid sequence of menin

The human gene MEN1 (also the name of the disorder associated with a mutant MEN1 gene) encodes the protein menin. UniProt specifies three isoforms of menin, Isoform 1 being called the 'canonical' sequence.¹ It is 615 amino acids in length, the others being 610 and 575 amino acids in length, respectively.

Menin Isoform 1:

        10         20         30         40         50         60
MGLKAAQKTL FPLRSIDDVV RLFAAELGRE EPDLVLLSLV LGFVEHFLAV NRVIPTNVPE

        70         80         90        100        110        120 
LTFQPSPAPD PPGGLTYFPV ADLSIIAALY ARFTAQIRGA VDLSLYPREG GVSSRELVKK 

       130        140        150        160        170        180 
VSDVIWNSLS RSYFKDRAHI QSLFSFITGW SPVGTKLDSS GVAFAVVGAC QALGLRDVHL 

       190        200        210        220        230        240 
ALSEDHAWVV FGPNGEQTAE VTWHGKGNED RRGQTVNAGV AERSWLYLKG SYMRCDRKME

       250        260        270        280        290        300 
VAFMVCAINP SIDLHTDSLE LLQLQQKLLW LLYDLGHLER YPMALGNLAD LEELEPTPGR 

       310        320        330        340        350        360
PDPLTLYHKG IASAKTYYRD EHIYPYMYLA GYHCRNRNVR EALQAWADTA TVIQDYNYCR 

       370        380        390        400        410        420
EDEEIYKEFF EVANDVIPNL LKEAASLLEA GEERPGEQSQ GTQSQGSALQ DPECFAHLLR 

       430        440        450        460        470        480 
FYDGICKWEE GSPTPVLHVG WATFLVQSLG RFEGQVRQKV RIVSREAEAA EAEEPWGEEA

       490        500        510        520        530        540 
REGRRRGPRR ESKPEEPPPP KKPALDKGLG TGQGAVSGPP RKPPGTVAGT ARGPEGGSTA

       550        560        570        580        590        600
QVPAPTASPP PEGPVLTFQS EKMKGMKELL VATKINSSAI KLQLTAQSQV QMKKQKVSTP

       610 
SDYTLSFLKR QRKGL 

The table contains standardized single-letter codes for the various amino acids. Wikipedia offers a table describing these codes.²
For example, the "Q" at amino acid position 64 represents glutamine, which is encoded either by codons CAA or CAG.³
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¹ UniProt entry on "MEN1_HUMAN"
² http://en.wikipedia.org/wiki/Amino_acid#Table_of_standard_amino_acid_abbreviations_and_properties (Wikipedia: Amino Acid).
³ http://en.wikipedia.org/wiki/Genetic_code#RNA_codon_table (Wikipedia: Genetic Code).

Cells use DNA methylation to control gene expression

• "Methylation of DNA (not to be confused with histone methylation) is a common epigenetic signaling tool that cells use to lock genes in the 'off' position."
• DNA methylation occurs at the cytosine bases of eukaryotic DNA, which are converted to 5-methylcytosine by DNA methyltransferase (DNMT) enzymes.
• ...methylation near gene promoters varies considerably depending on cell type, with more methylation of promoters correlating with low or no transcription.
• Although patterns of DNA methylation appear to be relatively stable in somatic cells, patterns of histone methylation can change rapidly during the course of the cell cycle. Despite this difference, several studies have indicated that DNA methylation and histone methylation at certain positions are connected.
• Tumor suppressor genes are often silenced in cancer cells due to hypermethylation.

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The Role of Methylation in Gene Expression. Theresa Phillips, Ph.D. 2008, Nature Education.

DNA methylation

Allfrey in 1964 described methylation as a chemical mark upon histones.^[Ref.1] According to newer sources, methylation also takes place on some CpG sequences of the DNA itself.^[Ref.11] CpG denotes a cytosine base next to a guanine base, a combination that tends to occur frequently. A methyl group (CH₃) may attach to the cytosine in a CpG pair, forming Me-CpG. DNA methylation is associated with the regulation of gene expression.

In human DNA about 80%-90% of CpG sites are methylated, but there are certain areas known as CpG islands where none of the sites are methylated. These are associated with the promoters of 56% of mammalian genes, including all ubiquitously expressed genes. ⁽¹⁾

MEN1 is a ubiquitously expressed gene^[Ref.6], so it would seem that we should take a closer look at methylation.
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⁽¹⁾Methylation. Wikipedia.

The Molecule that Shook the World

I've been reading a short book on DNA and genetics, and it has really surpassed my expectations. "DNA - A Graphic Guide to the Molecule that Shook the World", by Israel Rosenfield, Edward Ziff, and Borin Van Loon (2011, Columbia University Press), is designed much like a comic book. At first glance I didn't know whether to take the book seriously, but halfway through this little book I think it's a winner!

250 pages of serious material presented clearly and in a very readable, even entertaining form. DNA, replication, the genetic code, gene expression, chromosomes, epigenetics, the Human Genome Project, and much more... and every page illustrated to illuminate the material and to keep the reading brisk and with a sense of (occasionally bawdy) humor. This is a layman's book, a self-described "popular work" and "graphic novel". But unless You're a seasoned expert in the field, You may find this book very informative and enjoyable. Highly recommended.

This book may be one of the best, first sources to read for a layman who wants to begin to understand genetics and MEN1 a little more deeply.