Monogenic Hypertension

Thitisak Kitthaweesin MD.

Monogenic Hypertension

• HT is a major public-health problem

• Molecular pathogenesis in most patients remains poorly understand

• Genetic factors …known to play a role in determining inter-individual variation in BP.

Monogenic Hypertension

• There are mutations and polymorphisms that altering BP in human

• All the gene are involve directly or indirectly in control of Na reabsorption

• Mutations have been found in monogenic hypertension diseases that cause disorders of BP regulation

Dietary Na

Kidneys

Urinary Na

Renin

Blood volumeBlood pressure

Na transport

Aldosterone

ACTH

GRA

Adrenal hyperplasia

Deoxycorticosterone

MN receptor

Cortisol

Cortisone

ENaC(Liddle’s) Gordon’s

syndrome

Adducin

Angiotensinogen

Progesteronesensitivity

AME

Dietary Na

Kidneys

Urinary Na

Renin

Blood volumeBlood pressure

Na transport

Aldosterone

ACTH

GRA

Adrenal hyperplasia

Deoxycorticosterone

MN receptor

Cortisol

Cortisone

ENaC(Liddle’s) Gordon’s

syndrome

Adducin

Angiotensinogen

Progesteronesensitivity

AME

Glucocorticoid-remediable aldosteronism (GRA)

• AD monogenic HT

• Results from a chimeric gene product that place 18-hydroxylase (Aldosterone synthase) under control of ACTH promoter

• ACTH-regulated 18-hydroxylase activity is aberrantly expressed in Zona fasciculata and acts upon control to form 18-hydroxy cortisol and 18-oxocortisol

Aldosterone

• Adrenal hormones are synthesized in different areas of adrenal cortex– ZG…Aldosterone– ZF…Glucocorticoid (cortisol)– ZR…Androgen,estrogen

• ZG…well adapted for aldosterone production– low conc of 17-alpha hydroxylase– final step in conversion of corticosterone to ald

osterone

Aldosterone

• Aldosterone synthase

– >95% homology with 11-hydroxylase

– convert deoxycortisol to cortisol in ZF

– addition of hydroxyl group at C-18

– oxidation to an aldehyde

• Two distinct genes products perform terminal step in biosynthesis– 11 beta-hydroxylase (CYP11B1)…glucocorticoid

– 18-hydroxylase or Aldosterone synthase (CYP11B2)…mineralocorticoid

• Linkage analysis localized the gene to chromosome 8

• Chimeric gene consisting of the promoter-regulatory region of CYP11B1 and structural portion of CYP11B2 is localized between CYP11B2 and CYP11B1

• Protein product…perform all reaction required for aldosterone production >>>ACTH-dependent hyperaldosteronism

• Ectopic expression of chimeric protein express CYP17…formation of 18-hydroxy and 18-oxocortisol (biochemical hallmarks)

• Chimeric gene resulted from miotic mismatch and unequal crossing-over…located 5’ to intron 4 of CYP11B gene

GRA

ZF

ZGA II A II

ACTH ACTH

Aldo Aldosterone

CortisolCortisol

Aldo

- 18 OH Cortisol-OOO OOOOOOO18

l

ZG

ZF

Normal GRA

GRA

• Clinical…volume expansion

• Salt-sensitive HT

• Tend to have hypokalemic metabolic alkalosis

• Low renin-High aldostertone

• 18-OH and 18-oxocortisol in plasma and urine

• Replacement of prednisolone ameliorate HT & disappearance of abnormal stetroids

GRA and Pregnancy

• GRA not appeared to more prone to pre-eclampsia

• GRA…chronic HT, increased risk of exacerbation of HT during pregnancy

• Cesarean section rate > general and other obstetrics…2 folds

WycoffJAetal.Hyper t ensi on, 2 0 0 0

Apparent Mineralocorticoid Excess (AME)

• AR form of monogenic HT

• Results from inactivation of 11-beta-hydroxysteroid dehydrogenase type2 (11B-HSD2)

• Causing reduced metabolism of cortisol to cortisone…local cortisol excess and MN response

• Metabolic clearance of cortisol is prolonged in AME

• Excess urinary excretion of the reduced metabolites of cortisol… increased Tetrahydrocortisol:tetrahydrocortisone Ratio

Fredrick V. Osorio and Stuart L. Linus

AME

• Resembles the syndrome observed in persons integrity large amounts of licorice

• Volume expansion

• Salt-sensitive HT

• Hypokalemic metabolic alkalosis

• Low renin-Low aldosterone

• HT respond to thiazide or spironolactone but no aldosterone and abnormal steroid products in urine

AME

• Palermo et al. ( NEJM, 1998 )– Resolution of AME syndrome after KT in 38 ye

ar old woman– Abnormal ratio of reduced metabolite of cortiso

l/cortisonr in urine was not corrected– Ratio of urinary free cortisol to cortisone was c

orrected and correlated with the resolution of the syndrome

Liddle’s syndrome

• AD form of monogenic HT

• Volume expansion

• Salt-sensitive HT

• Hypokalemic metabolic alkalosis

• Low renin-Low aldosterone

• Not respond to spironolactone

• But triamterene can reduce BP

Liddle’s Syndrome

• A 16 yr-old girl referred with a provisional diagnosis of primary aldosteronism

• BP was consistently elevated at 180/120• Serum K was 2.6 mEq/l and serum HCO3

- 30 mEq/l

• The pt’s younger brother had BP 200/110,serun K 2.4 mEq/l and serum HCO3

- 29 mEq/l

Liddle’s Syndrome Workup

• Initial observation• Low rate of aldosterone secretion• No response to SV-9055,an inhibitor of

aldosterone secretion• No response to spironolactone, a

mineralocorticoid receptor antagonist • Triamterene a direct inhibitor of CCD Na+ and K+

transport , normalizes BP and serum K+• Renal transplantation normalize BP and serum K+

(Botero-Velez et al,NEJM 1994)

ENaC MUTATIONS IN LIDDLE’S

• 5 kindreds with c-terminal deletions of 45-75 amino acid in Beta-ENaC (Shimkets et al,cell,1994)

• 1 kindred with c-terminal of 76 amino acid in Gamma-ENaC

• 2 kindreds with missense mutation of Gamma-ENaC ( Hansson et al, Nature,1995)

• HYPERGENE data (Persu et al.Hypertension,1998)– Sequence analysis of Beta ENaC subunit in 532 HT proband

(101 low renin HT)

– Missense mutation in 7 unrelated individual,3 probands of African

– Mutation …T594M -6%, G442V -34.8%

NEDD4 protein binds to PY domain >>> internalized

and destroyPY domain

mutation,NEDD4 can’t

bind,internalize and destroy

Regulation of ENaC

-DanielaRotinCONH,2 0 0 0

Fredrick V. Osorio and Stuart L. Linus

Gordon’s syndrome

• One or more gene responible for Type II pseudohypoaldosteronism

• Linkage analysis to chromosome 1q31-q42, 17p11-q21, 12p?

• Type II pseudohypoaldosteronism in adults with HT( Gordon’s syndrome )– HyperK , intact renal Na conservation– Normal renal function, HT, low PRA, low to normal

PA– Normal antinatriuretic response to MN– But absent kaliuretic response– Distinguished from hyporenin/hypoaldosteronism by

• Normal renal function• Absent Hx of DM, uniform presence of HT• Absence of salt wasting when dietary NaCl restrict• Lack of kaliuretic response to MN

• Type II pseudohypoaldosteronism in adults with HT( Gordon’s syndrome )– Schambelan et al….primary defect may be related to

“enhanced Cl reabsorption in early distal tubule”…limit Na delivery to more distal tubule,decreased lumen negativity,impaired K secretion due to voltage-shunt effect

– Increased NaCl reabsorption expand ECF volume…HT and suppress RAAS

– Hyper K contributes to inhibition of renin secretion– PA..normal or suppressed depending upon balance

between inhibitory effect of volume expansion and stimulatory effect of hyper K

• Type II pseudohypoaldosteronism in adults with HT( Gordon’s syndrome )– Rx with thiazides or loop diuretics …enhance

renal H,K excretion…correct met acidosis, hyper K, HT, return PA&PRA to normal

Pseudohypoaldosteronism

• Type II pseudohypoaldosteronism in adults with HT( Gordon’s syndrome )

NaCl shunt

KH

NaCl reabsorption

Transtubular PD

ECF expansion

K/H secretion

hyperK

acidosis

Hyporenin/hypoaldo

Mineralocorticoid Receptor Defect

• Geller et al. ( Science, 2000 )• New mendelian form of HT caused by an activatin

g mutation in MR• Screened MR coding regions in 75 individuals ref

erred for evaluating monogenic HT• One patient…15 year boy with severe HT(210/120

mmHg), normokalemia, suppressed aldosterone level…Heterozygous for missense mutation altering Serine at codon 810 (S810) to Leucine (L810) …MRL810

Progesterone activates MRL810

• MR is a ligand-activated transcription factor

• Structures…– Long N terminal domain binds to transcription f

actors– Central DNA-binding domain– C terminal ligand-binding domain (LBD)

• L810 mutation in LBD altered receptor-ligand specificity

Progesterone activates MRL810

• No difference between receptor in response to MR agonosts ( aldosterone, cortisol)

• But MRL810 proned to have significant activity in the absence of ligand

• Antagonists of wild-type MR (progesterone)…potent agonists of MRL810

• Spironolactone… activated MRL810 …...contraindicated in MRL810

Pregnancy in MRL810

• 2 affected women and 5 pregnants

• Severe maternal HT, hypokalemia, hyperkaliuria

• Termination of pregnancy or early delivery

• No other signs of pre-eclampsia

• Support of in-vitro finding that progesterone agonized MRL810

Progesterone-induced Activation of MRL810

• Require a novel helix3/helix5 interaction

• S810 on helix 5 was near alanine 773 (A773) on helix 3 but distance is too great for stabilizing effect

• When L810 is substituted, longer non-polar leucine side chain come into close contact with A773

Progesterone-induced Activation of MRL810

• How does this interaction allow progesterone-mediated activation of MR?– Progesterone distinguished from MR agonists by a

bsence of C-21 hydroxyl group

– C-21 hydroxyl group form hydrogen bond with carbonyl group of asparagine 770 (N770) on helix 3…necessary for aldosterone-induced activation of MR

– In MRL810 …novel interaction of A773 with L810 replace this function

Helix3/helix5 interaction in progesterone mediated

activation of MRL810

2Geller DS et al. Science,000

Autosomal-dominant HT with brachydactyly

• First described bt Bilginturan et al. In 1973

• Dramatic increase in BP with age and die of stoke before age 50

• Map the gene to 12p

• PRA and aldosterone are normal

• Not salt-sensitive

• Normal RAAS and catecholamine response

Autosomal-dominant HT with brachydactyly

• Evidence of Neurovascular contact (NVC)– Left sided posterior cerebellar artery or ventricular

artery loop or bilateral– May result in hyperactive dysfunction of underlyin

g structures

• HT ...may related to increased sympathetic activity

Thank You