Growth in childhood Flashcards
Describe human growth
Human growth is an interaction between genetics, environment and nutrition. As such, growth is a measurement of health. In fact, chronic diseases in children often affect growth first.
Growth is a genetically pre-determined balance between cellular hyperplasia and apoptosis.
Note that not all systems mature at the same time, thus each organ or system has a period of vulnerability. If growth is perturbed during this period, it may cause organ damage or have systemic consequences.
Describe normal growth and its regulation
Normal growth is defined as the progression of changes in height, weight, and head circumference that are compatible with established standards for a given population. The progression of growth is interpreted within the context of the genetic potential for a particular child.
Growth is regulated by growth hormones, thyroid hormones and steroid hormones.
Describe the determinants of normal growth, and correlation between length and adult height
Somatic growth and biologic maturation are influenced by several factors that act independently and in concert to modify a child’s genetic growth potential.
The influence of maternal nutrition and intrauterine environment are reflected primarily in the growth parameters at the time of birth and during the first months of life, whereas genetic factors have an influence later in life.
The correlation coefficient between length and adult height is only 0.25 at birth, but increases to 0.8 at two-three years of age.
Foetal growth is determined mostly by nutritional factors and placenta:
- the placenta acts like an endocrine organ by releasing growth factors and hormones that interact and condition how the foetus is growing
- GH and IGF regulate the function of the placenta
The correlation coefficient between length and adult height varies with age:
- 0.25 at birth
- 0.8 at 2-3 years
- 0.9 at 14-15 years
Do the drivers that determine fetal weight also act in puberty?
Yes, determinants of foetal weight can also act in puberty. For example, there is a strong correlation between gestational maternal diabetes and autism/ADHD.
List the requirements for normal growth
- Emotional stability and a secure family environment.
- Adequate nutrition.
- Absence of chronic disease.
- Normal hormonal regulation.
- Absence of defects impairing normal cellular or bone growth.
Describe the genetic factors affecting growth
It is estimated that 70–90% of adult stature is genetically determined, nutritional and socioeconomic factors being equal. In addition to genetic factors affecting the production and response to insulin, thyroid hormones, sex steroids, and the GH-IGF1 axis, growth is controlled through genes acting in the growth plate (FGFs).
Homeobox genes are a group of genes with capacity to bind to DNA domains and regulate proteins. As such, they can alter the balance between hyperplasia and apoptosis.
At least 20% of causes of short stature are due to defects in hoemobox genes.
- PAX6 - Aniridia (Peter’s Syndrome)
- P**AX8 – Hypothyroidism due to thyroid dysgenesis
- MSX1 – Craniosynostosis
- **SHOX - Short stature in Turner and Leri-Weill SS.
- HESX1 – familial septo-optic dysplasia
Describe the GH-IGF axis
- Thyroid hormone fundamental for growth - children with thyroid deficiency do not progress in height
- Now diagnosed at birth with screening tools
- GHRH release from hypothalamus → GH release from pituitary in pulsatile manner
- Somatostatin shuts off the whole system
- Periods of rapid growth are separated by periods of no measurable growth
- Growth is also seasonal - growth velocities increase during spring and summer months
- Ghrelin produced by gut and stomach stimulates GH secretion
- Growth hormone:
- Act directly on cartilage
- Induce synthesis of IGF1 in liver → stimulate growth of cartilage in growth plate
- IGF1 circulates in blood in a complex → needs to be cleaved for IGF1 to be released
* Mutation in any component of this pathway can produce short stature
- IGF1 circulates in blood in a complex → needs to be cleaved for IGF1 to be released
- Homeobox gene mutations present with severe hypoglycaemia because regulatory hormones not
released (growth hormone, cortisol, etc.)
The GH-IGF axis has metabolic functions and works to:
- Increase lipolysis
- Increase protein synthesis
- Increase glucose levels
Describe the stages of growth
- Foetal growth, which is regulated by IGF-2 and GH. It is mostly dtemined by maternal nurtition and placenta (in turn regulated by GH and grwoth factors). The largest length grwoth occurs in the 2nd trimester thus any negative influences on the mother during this time will affect length. The average birth length is roughly 50 cm. The birth weight is mainly determined by the 3rd trimester
- Infancy, occurs within the first two years, and is largely determined by nutrition. The average growth is 35 cm per year.
- Childhood, in which growth is largely determined by GH. Growth rate decelerates to 5.5 cm/year. Growth either catches up or slows down. Until puberty, boys and girls grow at the same rate
- Puberty, which is determined by sex steroids and GH. Steroid hormones cause an increase in GH resulting in a growth spurt. When growth is low, weight is gained, and when growth is high, weight is lost. While the growth curve appears linear, velocity varies constantly.
The difference between girls and boys is between 10 and 12 cm.
Girls enter puberty approximately 2 years earlier.
Describe how growth is evaluated
- To determine the child’s growth percentiles, weight and length (or height) should be plotted on the appropriate growth chart at each well-child visit and as indicated at interval visits.
- Normal variants can be within 20% of the spectrum of growth
- Hypogonadotropism can be difficult to distinguish from late puberty
- The physical examination should include careful measurements of weight, length, and head circumference.
- Head circumference and weight-for-length should be plotted for children under 2 years
- BMI should be plotted for children older than 2 years
- Growth can be slowed or accelerated by a variety of conditions. Changes in growth may be the first sign of a pathologic condition.
- Growth velocity, the change in growth over time, is a more sensitive index of growth than a single measurement.
Describe how target height is determined
- plot target height using mother’s height plus 12.5 cm for boys or father’s height minus 12.5 cm for girls
- G2 - is the age at which the child starts puberty
Describe extrapolated height and its usefulness
Extrapolated height is not a good correlation, particularly at young age.
It relies on bone age.
Below puberty, it is difficult to do a height prognosis because he has a margin of 8.5 cm.
Describe the BMI and its use
The body mass index (BMI) characterizes the relative proportion between the child’s weight and the height squared. It is important to plot after age 2.
A child is considered overweight if it is greater than 85th percentile.
A child is obese if it greater than 95th percentile.
Describe relevant body proportions
The proportions of the body change during fetal and postnatal growth. The most commonly used descriptors of body proportions are the ratio of the upper body segment to the lower body segment and the ratio of arm span to height.
- Upper Segment to Lower Segment: The lower segment is measured from the top of the symphysis pubis to the plantar surface of the foot. The upper segment is calculated by subtracting the lower segment from the child’s height
- Arm Span to Height: The arm span is the distance between the tips of the middle fingers when the arms are raised to a horizontal position. A 10-15 cm difference is normal by age of 10 to 12 – where the arm span is bigger than height
Describe the differences in the onset of puberty between boys and girls
The first sign of puberty in girls is breast development.
This occurs around 10.5 years with peak velocity at 11.5 years.
The first sign of puberty in boys is the enlargement of testes.
This occurs around 11.5 years with peak velocity at 13.5 years.
List some causes of short stature
- Nutritional
- Constitutional delay
- Familial
- GH Related
- GHD/GH Resistance
- Hypothyroidism
- Sex Hormone Related
- Delayed puberty
- HGHG
- Glucocorticoid Excess
- Cushings/Iatrogenic
- Genetic Causes
- XO
- T21
- Syndromes
- Pseudohypoparathyroidism
- PWS
- LMB
- Skeletal dysplasias
- Miscellaneous
- GH Related
