Puberty and Growth Flashcards
WHO vs CDC growth curve
WHO
- Breastfed infants to 12m
- How kids should grow in ideal conditions
- No weight plot after age 10yrs – recommend plotting BMI only
- Addition of %iles – up to 99.9th and down to the 0.1th %iles
- International sample population (vs.US)
CDC
- Observational describe
how to measure growth proportions
1) U/L segment ratio
- lower segment = from the pubic symphysis to the ground while the child is standing straight with shoes off and feet
together
- upper segment= Subtract the lower segment from the total height
- Calculate ratio
**Normal is 1.7 in neonate to slightly below 1.0 in the adult.
2) Arm span
- Measure child’s arm span while she/he is standing with back touching wall and feet together. Arms should be fully extended against the wall and parallel to the floor with fingers together and outstretched, palms facing forward. Measure straight across (to length of 3rd finger), on the wall, once the child has stepped away.
**Should be ~ equal to height
3) Head circumference
- Measure from the occiput to the forehead around the head – objective is to measure maximal HC. Rpt 3x.
- Plot measurement on growth curve
Causes of abnormal proportions
Increased U/L
1. Achondroplasia
2. Hypochondroplasia
3. Turner
● Osteogenesis imperfecta
● Hypophosphatemic rickets
● (Pseudo)pseudohypoparathyroidism
Decreased U/L
1. Scoliosis
2. Spinal irradiation
where is GH produced/secreted
anterior pituitary somatotrophs
where is the Main organ GH acts to make IGF1
liver
GH receptor - what does it activate and cause
activates post receptor signaling through JAK/STAT
Leads to transcription of 3 important GH dependent genes:
IGF-1
IGFBP-3
ALS (acid labile subunit)
Growth hormone receptor pathway steps
- Dimerization of GH receptors
i. Different domains of a single GH molecule associate with homologous regions on 2 independent GH receptors, promoting dimerization of the receptors.
GH receptor lack a tyrosine kinase domain - Recruitment of JAK2 (Janus Kinase 2)
i. With dimerization, JAK2 is associated with and activated by the GH receptors. - Activation of JAK2’s intrinsic tyrosine kinase activity
i. JAK2 undergoes autophosphorylation and concurrently tyrosine phosphorylates the GH receptors - Recruitment of STAT (Signal Transducer & Activator of Transcription) Factors:
i. The phosphorylation of the GH receptors by JAK2, provides a docking station for STAT factors (STAT5a & STAT5b are most relevant to GH). - Transcription
i. STATs are phosphorylated. They dissociate from the GHR, migrate to the nucleus, and bind to specific STAT-binding DNA regulatory elements (SIE/ISRE/ GAS) responsible for transcriptional control of GH target genes such as IGF-1.
Pharmacologic agents that stimulate secretion of GH
- AMINO ACID
Arginine - NEUROTRANSMITTER
Clonidine (alpha adrenergic agonist)
L-dopa (dopamine agonist)
Propranolol (beta-adrenergic antagonist)
GABA agonists (muscimol)
ALPHA AGONIST
BETA ANTAGONIST
- HYPOGLYCEMIA
Glucagon (relative hypoglycemia)
Insulin (hypoglycemia) - HORMONES
GHRH
Peptide–ACTH, alpha-MSH, vasopressin
Estrogen - OTHER
Potassium infusion
Physiologic stimulants for GH
Hypoglycemia
Exercise
Sleep
Stress
Protein depletion/starvation/AN
Chronic renal failure
Ectopic production of GHRH
Acromegaly (TRH, GnRH)
physiologic inhibitors of GH secretion
Hyperglycemia (postprandial)
Elevated FFA
Obesity
Hypo or hyperthyroidism
Somatostatin
Progesterone
Glucocorticoids
Alpha adrenergic inhibition
Beta adrenergic stimulation (GH)
what hormones are involved in growth
Growth hormone
Thyroid hormone
Sex steroids
Corticosteroids
Growth hormone - other name
- stimulated by
- inhibited by
somatotropin
stimulated by GH-releasing hormone (GHRH or GRF)
suppressed by hypothalamic GH release-inhibiting factor (somatostatin or SRIF)
what does GH do directly, besides IGF1
stimulates lipolysis,
increased amino acid transport into tissues,
increased protein and glucose synthesis in liver
also has direct effect on cartilage growth
how is GH secreted throughout day
in a pulsatile manner
Clinical Signs of GH deficiency
- Poor growth
(increased fat mass leading to a chubby or cherubic appearance with immature facial appearance, immature high-pitched voice, and delay in skeletal maturation)
midface hypoplasia - Neonatal Hypoglycemia
- Prolonged jaundice
- Micropenis
- breech position
- delayed dentition
- giant cell hepatitis
- midline defects
- higher incidence of hyperlipidemia with elevated total cholesterol and low-density lipoprotein
what agent can be used for a GH stim test
L-Dopa
Clonidine
Arginine
Glucagon
Insulin-induced hypoglycemia (very dangerous)
GHRH
Growth hormone–releasing peptides (GRP)
how do corticosteroids affect growth
if XS - poor growth
if low, not a big effect if well otherwise
Acquired causes of GH deficiency
Hypothalamic-pituitary tumors
Histiocytosis X
Central nervous system infections
Head injuries
GH deficiency following cranial irradiation
Central nervous system vascular accidents
Hydrocephalus
Empty sella syndrome
Syndromes/Conditions w Short Stature + Obesity
Laurence-Moon
Biedl-Bardet
Prader-Willi syndrome
hypothyroidism,
glucocorticoid excess,
pseudohypoparathyroidism with Albright Hereditary Osteodystrophy
achondroplasia
gene
features
FGFR3 mutation
frontal bossing
mid-face hypoplasia
exaggerated lumbar lordosis
limited elbow extension
genu varum
trident hand
motor delay
spinal stenosis
obesity
intelligence normal
Russell silver syndrome
criteria for dx
4/6 of:
- SGA (birth weight and/or length ≥2 SD below the mean for gestational age)
- Postnatal growth failure (length/height ≥ 2 SD below the mean at 24 months)
- Relative macrocephaly at birth (HC >1.5 SD above birth weight and/or length)
- Frontal bossing or prominent forehead (forehead projecting beyond the facial plane on a side view as a toddler [1–3 years])
- Body asymmetry (limb length discrepancy ≥0.5 cm, or <0.5 cm with ≥2 other asymmetric body parts)
- Feeding difficulties or body mass index ≤2 SD at 24 months or current use of a feeding tube or cyproheptadine for appetite stimulation
what does SHOX stand for
Short stature HOmeoboX-containing gene
Noonan syndrome
short stature, webbed neck, low posterior hairline, and facial resemblance to Turner syndrome, but the karyotype is 46,XX in the female or 46,XY in the male
Prader Willi Syndrome
poor intrauterine movement,
acromicria (small hands and feet),
developmental delay
almond-shaped eyes along
infantile hypotonia
poor feeding as infant
short stature
insatiable hunger
obesity
glucose intolerance
delayed puberty
Prader Willi syndrome gene
lack of expression of paternally inherited imprinted genes on chromosome 15q11-13
when to stop GH therapy
GV <2cm/y
BA fused
GH Tx Side Effects
intracranial hypertension
slipped capital femoral epiphysis (SCFE)
scoliosis progression
Insulin resistance
Theoretical increased risk of malignancy
Gynecomastia (for boys)
Local reaction at site of injection
Increased growth of nevi (?)
Hypertrophy of tonsils/adenoids (?)
Laron syndrome
= GH insensitivity
Molecular mechanism:
- Primary GH resistance - Receptor mutation (decreased or absent).
Note: Decreased serum GHBP levels
- GH insensitivity - Post-receptor defects.
Note: Normal GHBP levels
- Primary IGF-1 deficiency – synthesis or receptor
Autosomal recessive
GH elevated due to decreased or absent IGF-1
Does not respond to GH treatment… need recombinant IGF-1
Causes of tall stature: nonendocrine
- constitutional tall stature
- genetic tall stature
- syndromes of tall stature
—Kilnefelter
—Marfan
—-Cerebral gigantism
—Homocystinura
—Beckwith-Wiedemann - XYY and XYYY syndromes
Causes of tall stature: endocrine
Pituitary gigantism
Sexual precocity
Thyrotoxicosis
IDM
GH excess - names
pituitary gigantism before epiphyseal fusion
acromegaly after
pituitary gigantism - features
Grow excessively rapidly,
coarse features,
large hands and feet with thick fingers and toes, and
often frontal bossing and large jaws
glucose intolerance or frank diabetes mellitus,
hypogonadism, and
thyromegaly
pituitary gigantism - causes
- GH secreting pituitary adenoma or somatotrophs
- constitutive activation of GH secretion as is sometimes found in the McCune-Albright syndrome
- excess secretion of GHRH
ectopic GH secretion (rare)
thyrotoxicosis and growth
increased growth, advanced bone age, and, if occurring in early life, craniosynostosis
how to test for pituitary gigantism
GH suppression test with OGTT
1.75g/kg oral glucose (max 75g)
measure serum GH before and two hours after glucose administration
GH should be <1 or 5 ng/L depending on resource
effects of anorexia nervosa
- GH axis: low IGF1, normal or high GH
- insulin: low
- cortisol: high
- thyroid: sick euthyroid
- hypogonadotropic hypogonadism
- decreased leptin and oxytocin
- increase ghrelin, peptide YY and adiponectin
Signs of estrogenization
- Breast development (mainly from E, but other factors too)
- Areolae become more pigmented and erectile as development progresses
- Enlargement of the labia minora and majora
- Dulling of the vaginal mucosa from its prepubertal reddish hue to pink (due to cornification of the vaginal epithelium),
- Production of a clear or slightly whitish vaginal secretion prior to menarche
Start of central puberty in males
- physiology
Starts with testicular enlargement
2.5cm or 4ml
Most of the increase in testicular size is due to seminiferous tubular development secondary to stimulation by follicle-stimulating hormone (FSH), with a smaller component due to Leydig cell stimulation by luteinizing hormone (LH)
hCG secreting tumour - what happens to male testes
Leydig cells are stimulated by LH (not FSH) so the testis does not grow as large as in normal puberty. (but they do enlarge)
mechanism of earlier puberty in obese females
local aromatase activity in adipose tissue
how does estrogen affect growth
- indirectly stimulates IGF-I production by increasing the secretion of GH
- directly stimulates IGF-I production in cartilage
- stimulating maturation of the chondrocytes and osteoblasts, ultimately leading to epiphysial fusion