Endocrine Flashcards
Diagnosis of diabetes
- Fasting BSL >7mmol/L (no caloric intake for 8hrs)
- 2hr plasma glucose >11.1 during OGTT (glucose load of 1.75g/kg, max 75g)
- Random BSL >11.1 in a pt with Sx of hyperglycemia or DKA
- HbA1c >6.5% (paediatric patients = 6.35%)
Premature thelarche
- Isolated breast development - slow progression
- Absence of other secondary sexual features
- Normal linear growth
- Normal bone age - important
- Peaks at around 2yo and again at 6-8yo
- Soy based formulas, lavender oil and tea tree oil - ??increased risk of premature thelarche
When to investigate “premature thelarche”
- Progressive secondary sexual development
- Increasing height velocity
- Accelerated bone maturation
GnRH dependent (central) precocious puberty
- Early maturation of hypothalamic-pituitary-gonadal axis
- Characterised by evidence of sustained sex steroid exposure:
- -> Accelerated linear growth
- -> Advanced bone age
- -> Progressive pubertal clinical changes
- -> Pubertal levels of FSH and LH (GnRH test: LH dominant with levels >5)
- -> Pubertal levels of oestradiol in girls, T in boys
- Ix with GnRH (leucrin) stimulation test
Causes of central precocious puberty
- Idiopathic (F>M)
- Loss of hypothalamic inhibition: structural growths
- -> Hypothalamic hamartomas - CNS tumours e.g. astrocytoma, pineal gland tumours, optic gliomas
- Acquired CNS insults e.g. CNS irradiation, hydrocephalus, subarachnoid cysts, CP, tub sclerosis
- Neurofibromatosis type 1 (optic glioma)
- Previous excess sex steroid exposure e.g. poorly controlled CAH
- Genetic e.g. gain of function mutation of kisspeptin gene, MKRN3 gene mutation (imprinting)
Treatment of central precocious puberty
- Administration of Leuprolide depot every 3mths
- GnRH analogue: provides constant serum GnRH which over-rides pulsatility of endogenous GnRH –> secondary feedback inhibition
- Effects: initially see a surge in LH/FSH, then as the GnRH receptor becomes desensitised, subsequent secondary inhibition
- Protocol: 11.25mg IM 3mthly with a review with LH level 1hr post-dose
- -> LH <2 = adequate suppression
- F/u: annual GnRH test and bone age
Long term outcomes after treatment with Leuprolide in central precocious puberty
- Height: greatest height gain seen in girls with onset of puberty <6yo (average gain 9-10cm)
- Menstrual cycles and fertility appear normal as adults
- Possible increased incidence of PCOS
McCune-Albright Syndrome
Cafe-au-lait spots
- Irregular “Coast of Maine” lesions
- Rarely cross midline
- Increases with age
Peripheral precocious puberty (cyst-related)
Polyostotic fibrous dysplasia (develops slowly over time)
- Need to continuously screen for it
Other manifestations: phosphate wasting, GH excess, Cushing’s, thyrotoxicosis, cardiac arrhythmias, cholestasis
Pathogenesis of McCune-Albright Syndrome
- Somatic mutation - not inherited
- Constitutive activation of alpha-subunit of G3 protein that activates adenylyl cyclase
- Affects signal transduction of multiple G protein coupled receptors e.g. LH, FSH, GHRH, TSH, ACTH, PTH, catecholamines etc
Causes of gonadotrophin-independent (peripheral) precocious puberty in girls
McCune Albright Syndrome Ovarian cysts Ovarian tumours Exogenous oestrogen exposure Adrenal tumours (aromatisation of T) CAH Primary hypothyroidism (TSH cross-reacts w/ LH/FSH-R) Pituitary gonadotrophin secreting tumours (rare)
Causes of gonadotrophin-independent (peripheral) precocious puberty in boys
McCune Albright Syndrome
Leydig cell tumours
HCG secreting tumours
Familial male-limited precocious puberty (LH-R mutation)
Exogenous oestrogen exposure
Adrenal tumours
CAH
Primary hypothyroidism (testicular enlargement only)
Pituitary gonadotrophin secreting tumours (rare)
What is the primary reason for short stature in Turner Syndrome?
Haploinsufficiency of SHOX gene
- SHOX gene is located at distal ends of short arms of both sex chromosomes
Risk of germ cell tumours in DSD conditions
High-risk requiring gonadectomies:
- Dysgenetic gonads (+Y) that are intra-abdominal 15-35%
- PAIS (non-scrotal) 50%
- Frasier syndrome 60%
- Denys-Drash (+Y) 40%
- Turner (+Y - mosaic?) 12% (intermediate risk)
Intermediate risk for germ cell tumours
- For monitoring +/- Bx
- 17B-HSD 28%
- Dysgenetic gonads (+Y) - unknown risk –> Bx
- PAIS (scrotal glands) - unknown risk –> Bx
When is the best time to take a cortisol level?
Early morning (+/- ACTH stimulation)
- Crucially time-dependent
- Regulated by stress and circadian rhythm
- By midnight –> minimal cortisol, by 2am –> start producing cortisol, by 6-9am –> maximal concentration should be reached
Incidence of classical CAH in female
1/28,000
When do physiological pre-pubertal gonadotrophin surges occur?
- Mid-gestation: LH/FSH levels peak, then decline/disappear by term
- Second surge between 30-100 days of life: “mini-puberty of infancy”, can utilise this opportunity for a “free” stimulation test
- If ex-premature infant, perform at CGA
“Pro-testis” factors
- SOX9 gene: influences expression of SRY
2. SRY gene: transcription factor which promotes the development of testes, Sertoli and Leydig cells
Camptomelic dysplasia
- AD, translocation w/ breakpoint at 17q24-25 or deletion of 17q
- Excess female phenotype in 46XY –> absence of SOX9 –> no SRY gene product
- CF: pierre robin sequence, short bowed limbs, dislocatable hips, 11 ribs, club feet, laryngotracheomalacia, C-spine instability
- Early neonatal death is common
Genes responsible for development of bipotential gonads
LIM1, SF1, WT1
Denys Drash Syndrome
- Missense mutation in WT1
- If 46XY, cannot express full testicular development and vice versa for 46XX
- CF: mesangial sclerosis causing early, infantile nephrotic syndrome –> early renal failure, increased risk of Wilm’s tumour (aggressive)
WNT4 deletion in 46XX
- WNT 4 is a “pro-ovary factor” that promotes development of mullerian structures
- 46XX DSD - no germ cells, ovarian failure and mullerian agenesis
Adrenal hypoplasia congenita
DAX1 deletion
Tests to consider in ovotesticular DSD/46XX testicular/46XY complete gonadal dysgenesis
i.e. “True hermaphrotidism”
Blood karyotype Scrotal skin fibroblast biopsy Gonadal biopsy - Need to identify genotype/karyotype - Usually due to mosaicism or chimerism
CAH: 21-hydroxylase deficiency
- No cortisol!
- Circulatory collapse - 80% - no aldosterone, 20% produce aldosterone
- Na wasting, hyperkalemia with acidosis - 46XX DSD: virilisation due to shunting of cholesterol by-products down androgen synthesis pathway
- 46XY: normal male genitalia
CAH: 11-beta hydroxylase deficiency
- Further down steroidogenesis pathway
1. 11-DOC = weak mineralocorticoid (excessive amts) –> high Na, hypertension
2. 46XX DSD (mild virilisation)
CAH: which enzyme deficiency causes a 46XY DSD?
- 17B-hydroxysteroid dehydrogenase: involves androgen pathway only
- 3B-hydroxysteroid dehydrogenase: able to produce DHEA, but low androstenedione; Na wasting and low cortisol
- 17a-hydroxylase: rare, HTN and hypoK with renin suppression, sex hormones cannot be synthesised correctly
- Reduced androgen production –> undervirilisation of 46XY
Differential diagnoses for an isolated micropenis
- Familial
- Idiopathic
- Hypopituitarism (assoc. undescended testes)
- Prader-Willi Syndrome
- Floppy neonate with feeding problems
Mechanism of micropenis in hypopituitarism
- Usually, there is a gonadotrophic surge in 3rd trimester, which does not occur if there is hypopituitarism
- Underdeveloped (not ambiguous!) genitalia with micropenis and undescended testes
Congenital anorchia
“Disappearing testes”
- 46XY DSD: undervirilised due to reduced testosterone production
- Possible intrauterine torsion
Antimullerian hormone defect
46XY with uterus/mullerian structures
- Normal male genitalia
- However, due to absence of AMH, mullerian structures also persisted and developed internally
- Usually presents with “herniation” and incidentally found during surgery
- Normal male phenotype after removal of mullerian structures
Investigations for isolated micropenis
Rule out hypopituitarism (MRI)
Genetic testing for Prader-Willi (if suspected clinically)
At +30 days, test for testosterone, LH, FSH levels
- If abN: further Ix for central hypogonadism (DDx: Kallman syndrome)
- If normal: counsel family, ?testosterone replacement therapy
Investigations in neonatal period for ambiguous genitalia
Neonatal period:
- USS to assess internal organs (day 1)
- Karyotype (day 1)
- Electrolytes and BSL (day 1-2)
- 17-OH (day 4+)
Day 30+:
- Testosterone, oestrogen, LH, FSH - time with “minipuberty”
- Cloacogram (pre-surgery for planning)
- At 18mo, if complex DSD suspected: laparoscopy with biopsy of internal structures, scrotal skin biopsy (fibroblasts) for chromosomes, androgen receptor studies
Management/support for DSDs
- Address Q’s regarding fertility, sexuality; avoid stereotyping/gender bias etc etc
- Medical treatment as required
- Gender surgery
- Delay constructional surgery
- Primary duty is to child
- Limited evidence of good outcome
- Base advice on evidence not personal opinion
- Excision surgery must have clear indication - Screen for malignancy: gonadectomy vs biopsy vs monitor
- Psych support
Causes of adrenal insufficiency
- Tertiary: hypothalamus
- Tumour, malformation
- Iatrogenic: high dose corticosteroid therapy - Secondary: pituitary
- CRH receptor defect, isolated ACTH def
- Panhypopit - Primary: adrenals
- Acquired vs congenital
Waterhouse-Friederichsen syndrome
Haemorrhage into adrenal glands –> acquired adrenal insufficiency
- Meningococcus septicaemia
- Stressed neonate (e.g. extreme preterm)
Natural course of autoimmune Addison’s disease
- Antibody formation against 21-OH, SCC, 17-OH
- Increasing resting plasma RENIN
- Raised afternoon ACTH
- Depressed ACTH-stimulated cortisol response
- When 90% of adrenal function depleted = disease manifestation - decreased aldosterone and cortisol
APECED Syndrome
- Mutation in AIRE gene (21q22.3) - autoimmune regulator
- Autoimmune adrenalitis, hypoparathyroidism, mucocutaneous candidiasis
Autoimmune polyendocrinopathy (APS) 2
Autoimmune adrenalitis
Autoimmune thyroiditis
T1DM (dififcult to control due to adrenal antibodies)
Other features common to APS 1 and 2
Chronic active hepatitis (cause of mortality), malabsorption, alopecia, vitiligo, pernicious anaemia and hypogonadism
Pathogenesis of hyperpigmentation in Addison’s
ACTH and MSH formed from POMC –> excess ACTH can bind cutaneous melanocortin-1 receptor
Triple A syndrome
- Adrenal insufficiency
- Alacrima
- Achalasia
- Neurological impairment with early onset dementia
Long term steroid (cortisol) replacement
Hydrocortisone:
- Suppressive dose = 10-15mg/m2/day
–> CAH: suppress androgens to reverse virilisation
- Replacement dose = 6-10mg/m2/day
–> Secondary adrenal failure (20% higher than baseline production)
- Stress (e.g. infection): 3-5 fold increase in HC dose
- Surgery: IV 100mg/m2/day on day 1 and 2
Fludrocortisone: ~0.1mg/day
Monitoring hydrocortisone dose long term in CAH patients
Monitor with height velocity and bone age
- Excessive HC: weight gain –> reduced growth velocity –> delayed bone age –> decrease dose
- Insufficient HC: continue androgen production –> increased height velocity –> increased bone age (leading to short stature) –> reduce dose
- If androgen control still poor, add fludrocortisone
Effect of pH on plasma calcium
- Low pH: increased ionised calcium
- High pH: decreased ionised calcium
Hormones that affect plasma Calcium
Increase plasma Ca:
- GH (through IGF1)
- Thyroxine
- Oestrogens
Decrease plasma Ca:
- Glucocorticoids: inhibits osteoclast formation+activity, long term - decreases protein synthesis in osteoblasts, decreases intestinal absorption of Ca, increase Ca excretion
Phosphate
- Major control of P: renal
- -> Increased excretion mediated by PTH binding to receptors in proximal tubule
- -> Reabsorption primarily occurs in proximal tubule - easily saturable process –> urinary spillover if high P
- Buffered by Ca and bone
- Gut absorption is linearly related to dietary intake
PTHrP
- Critical for normal foetal development
- -> Most important hormone in maternal-foetal Ca transfer
- -> Widely expressed in many tissues, modulator of cell growth and differentiation
- Paraneoplastic phenomena: mediator of syndrome of “humoral hypercalcemia of malignancy”
Effects of PTH
Chromosome 11, 1/2 life = 10min
Stimulated by hypocalcemia and hyperphosphatemia
Mechanism:
- Major = bone mobilisation - increased osteoclast activity
- Increased renal reabsorption at DCT, increased PO excretion
- Stimulates 1a-hydroxylase enzyme to increase Vit D hydroxylation
Effects of Vitamin D (1,25-VD)
- Major: Increased Ca and PO reabsorption in small intestine (jejunum)
- Increases osteoclast activity in bone
- Increased renal tubular reabsorption of calcium and phosphate
Major source of vitamin D
- Skin (>80%): 7 dehydrocholesterol in skin –> Vit D3 by UVB light
- Diet (10%): Vitamin D2 (ergocalciferol)
Risk factors for Rickets of Prematurity
Ca and P deficiency - def of Phos > Ca
- Prematurity (80% of Ca/P transfer in utero occurs in 3rd trim)
- BW <1000g
- Cholestatic jaundice
- Complicate neonatal course
- Prolonged TPN
- Soy formula/breast milk without fortification
- Medications: corticosteroids, diuretics
- Poor vitamin D intake
Risk factors for Vitamin D Deficiency Rickets
- Unsupplemented, prolonged breastfeeding + late weaning (BM Vit D = <25IU/L)
- Maternal Vit D deficiency
- Dark skin ethnicity
- Decreased sun exposure
- Malabsorption
- AEDs
Biochemical abnormalities in Vitamin D Deficiency Rickets
- Hypocalcemia
- N/Low phosphate –> P wasting due to PTH activity
- High PTH and ALP
- Low Vitamin D (esp 25-D = storage form)
- -> Monitor response to therapy by measuring 25-D levels
Biochemical abnormalities in Rickets of Prematurity
- Hypophosphatemia (inadequate intake/reduced in utero transfer)
- -> Appropriate renal response = low P in urine
- Calcium levels are variable (low/N/high)
- -> 1,25-D activated due to low P –> increased intestinal absorption, unable to be stored in bone (due to low P - cannot form hydroxyapetite), excreted in urine
- Normal 25-D, N/high 1,25-D (low P activates renal 1a-hydroxylase)
- High ALP (>x5-6 ULN is suggestive of diagnosis)
- -> Increased bone demineralisation
PHEX gene
Phosphate regulating endopeptidase on X chromosome
- Present predominantly in bone and teeth
- Product of PHEX gene degrades and inactivates hormone-like substances that promote phosphate excretion + impair bone mineralisation
- Indirectly inactivates FGF23
Fibroblast growth factor 23 (FGF-23)
Humoral mediator that decreases renal tubular reabsorption of phoshate and decreases activity of renal 1a-hydroxylase activity
Familial hypophosphatemic rickets
a.k.a Vitamin D resistant rickets
- X-linked mutation in PHEX gene –> increased levels of FGF-23
- Males are affected with full phenotype, affected mothers may only have fasting hypophosphatemia
- Defect in PO reabsorption (renal wasting) –> phosphaturia
- Defect in hydroxylating 25-Vit D
- CF: rickets esp lower limbs, poor growth, delayed dentition, tooth abscesses
- Ix: Low PO, Low 1,25 Vit D, normal Ca/25-Vit D/PTH, high ALP due to poor mineralisation
- Tx: oral phosphate and calcitriol
Excess 1,25-Vit D (excessive doses of calcitriol)
Hypercalcaemia –> hypercalciuria (renal reabsorption mechanism becomes saturated) –> nephrocalcinosis
Excessive phosphate supplementation
High P –> reduced Ca (increased binding, decreased 1,25-D conversion)
Stimulates PTH –> worsens bone reabsorption –> decreased mineralisation and #
Calcitonin
Produced by parafollicular cells of thyroid in response to hypercalcemia
Stimulates Ca deposition in bones
Decreases Ca absorption in intestines
Promotes Ca excretion in kidneys
Calcium-sensing receptor
- CaSR of parathyroid gland continuously senses serum ionised Ca
- Class C G-protein coupled receptor –> phosphoinositide turnover
- Rapidly adjusts PTH release for even minute changes in ionised Ca levels
- -> When active, inhibits PTH secretion
- CaSR in renal tubules has direct effect on calcium reabsorption
Biochemical defects in hypoparathyroidism
Normally, PTH: increases bone resorption –> increase Ca, increases renal PO excretion
- Low serum Ca, normal/high PO4
- Low urinary Ca
- Inappropriately normal or low PTH
- ALP low/normal
Other: calcification of basal ganglia, cataracts, long QT
Pseudohypoparathyroidism Type 1A - clinical features:
- Inactivating mutation of GNAS (maternally inherited mutation)
- TSH resistance - <2yrs, usually presents first,
- PTH resistance - presents in infancy or later
- GHrH resistance in pituitary - contributes to short stature
- FSH/LH resistance - menstrual irregularities in older girls
Other: brachydactyly 3-5th fingers, syndactyly 2-3rd toes, subcutaneous calcifications, cataracts, short stocky build with round face, flat nasal bridge and short neck, mental retardation
Pseudopseudohypoparathyroidism
Same inactivating mutation of GNAS inherited from father = Albright hereditary osteodystrophy phenotype without endocrine dysfunction
Recall: tissue-specific parental imprinting of GNAS
Vitamin D deficiency
- Based on 25-OH Vit D level
- Deficiency = <50nmol/L
- Insufficiency = 50-<75nmol/L
Treatment of Vitamin D Deficiency (acute therapy)
- Age <1mth: 1000IU (25microg) daily for 3/12
- Age 1-12mth: 3000IU (75microg) daily for 3/12
- Age >12mth: 5000IU (125microg) daily for 3/12
OR Stoss therapy (noncompliance risk): high dose of Vit D3 at beginning of winter to maintain Vit D level
- 300,000 - 500,000IU as once off dose
- Vit D3 stored in fat –> very long half life
DDx for vitamin D deficiency rickets
- Calcium deficiency
- Type 1 Vit D dependent rickets: 1-alpha hydroxylase deficiency
- Type 2 Vit D dependent rickets: mutation in vit D receptor, end-organ resistance to 1,25-OH
- Hypophosphatemic rickets
- -> X-linked
- -> RTA
- -> Hereditary hypophosphatemic rickets w/ hypercalciuria
- -> Nutritional phosphate deficiency