Dr. Jeffrey Baron
What causes some children to have growth problems and be extremely short as adults? This was the question raised at the 8th annual John Laws Decker Memorial Lecture,
an event that features the winner of the Distinguished Clinical Teacher Award (DCTA).
Dr. Jeffrey Baron, chief of NICHD’s section on growth and development, is the 2011 DCTA winner and was recognized for excellence in mentoring health care professionals and teaching
on issues related to patient care. His talk covered three major areas: the factors that regulate
growth, how these factors cause growth defects in children and treatments for children experiencing growth problems.
“The central concept in this field is that children get taller because their bones get longer. And their bones get longer because of the growth plate, a thin layer of cartilage that is found in vertebrae and at the ends of long bones,” Baron said.
Childhood growth is carefully regulated by multiple factors including hormones, genes and nutrition. “If we want to understand childhood growth and growth disorders, we have to understand the regulation at each of these levels,” Baron said.
The presence of growth hormone, for example, is important for normal childhood growth. But diagnosing growth hormone deficiency is not easy. For one thing, it is hard to get an accurate reading of how much growth hormone a child’s body is making. Current tests for growth hormone deficiency often yield false positive results. “In my opinion, we’re over-diagnosing growth hormone deficiency left and right,” Baron said.
He also explained that what looks like growth hormone deficiency may really be growth hormone insensitivity, meaning the body makes growth hormone but cannot properly respond to it.
What roles do other hormones play? Glucocorticoid has a slowing effect on growth. Others, like thyroid hormone and androgen, have accelerating effects on growth. The hormone estrogen, however, reveals a more complicated story.
Baron explained that when a child comes into the office with a growth problem, “You have to consider hundreds of diagnoses with each individual.”
Photos: Bill Branson
“When it comes to estrogen, it’s often said it’s a two-edged sword,” Baron noted. While estrogen can accelerate growth, it can also accelerate aging of the growth plate and hasten the time at which growth will stop. Children also need good nutrition to grow properly— meaning the right amount of calories and nutrients. Poor nutrition can affect hormone levels in a way that negatively affects growth. For example, children who are not getting proper nutrition might be able to produce growth hormone, but their bodies cannot properly respond to it. Baron said that in this way, “Malnutrition can be thought of as an acquired form of growth hormone insensitivity.”
He further explained that our bodies have evolved to conserve energy in times of starvation. “Growth is a luxury that can be postponed for better times,” Baron said.
Another piece of the childhood growth puzzle lies in our genes. Researchers have identified over 200 genes required for normal growth plate function. A mutation in the SHOX gene, for example, can lead to severely abnormal skeletal growth.
How do we diagnose and treat children with growth problems? Baron explained that when a child comes into the office with a growth problem, “You have to consider hundreds of diagnoses with each individual.”
Doctors start by charting a child’s growth curve and can move into more complicated assessments like genetic testing. After diagnosis, treatments can include medications that increase the rate as well as the duration of growth. Injections of growth hormone have successfully increased the rate of growth but remain controversial because the long-term safety of the treatment is unknown.
Researchers are cautiously optimistic about treatments that extend the duration of growth, including one drug still in clinical development that can “shut off” estrogen as a way to prolong growth. Baron noted that this drug and several others have great potential but are not yet ready for “prime time.”
Baron thanked the fellows in the Endocrinology Training Program who nominated him for the teaching award. “It’s one of the great pleasures of this job,” said Baron. “To teach you, to learn with you and to take care of patients together.”
The lecture honors the memory of Dr. John Decker, director of the Clinical Center from 1983 to 1990. He oversaw major advances at the CC, including the development of the positron emission tomography program and the clinical use of magnetic resonance imaging.