IB Biology SL1
3.3.3 Marfan Syndrome
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adapted from
http://web.mit.edu/esgbio/www/mg/geneticcounseling.html
http://www.marfan.org/nmf/GetContentRequestHandler.do?menu_item_id=2
Marfan syndrome is a heritable dominant condition that affects the connective tissue. The primary purpose of
connective tissue is to hold the body together and provide a framework for growth and development. In Marfan
syndrome, the connective tissue is defective and does not act as it should. Because connective tissue is found
throughout the body, Marfan syndrome can affect many body systems, including the skeleton, eyes, heart and
blood vessels, nervous system, skin and lungs.
Marfan syndrome affects men, women and children, and has been found among people of all races and ethnic
backgrounds. It is estimated that at least 1 in 5,000 people in the United States have the disorder
Some common features of the syndrome (not all are present in all cases):
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long (relative to height),
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flat feet
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dislocated eye lens
thin limbs
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spinal curvature (scoliosis)
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detached retina
prominent shoulder blades
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protruding or caved-in
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long fingers & thumbs
breastbone
It also causes heart valve abnormalities and weakening of the aortal wall. During heavy exercise, the weakened
aortal wall can burst, leading to almost instantaneous death.
Diagnosis
Although the gene for Marfan syndrome has been found, there is no simple blood test or skin biopsy to make the
diagnosis. The diagnosis needs to be made after examinations by a number of doctors, including a doctor who
specializes in bones (orthopedists), eyes (ophthalmologist) and heart (cardiologist), as well as a medical
geneticist (a doctor with special knowledge about inherited diseases). The exam includes:
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information about any family members who may have the disorder or who had an early, unexplained
heart-related death
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a thorough physical examination, including an evaluation of the skeleton for the ratio of arm/leg size to
trunk size and other changes that affect the bones and joints
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an eye examination, including a "slit lamp" evaluation by an eye doctor (ophthalmologist) after fully
dilating the pupil
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heart tests such as an echocardiogram (a sound-wave picture) by a heart doctor (cardiologist) used to
examine the heart valves and aorta.
One doctor coordinates the findings from all examinations. The medical geneticist most commonly handles this.
The doctor may diagnose the Marfan syndrome if the patient has a family history of the condition and there are
specific problems in at least two of the body systems known to be affected. For a patient with no family history of
the disorder, at least three body systems must be affected before a diagnosis is made. In addition, two of the
systems must show clear physical signs that are relatively specific for the Marfan syndrome.
A Case Study in Genetic Counseling
Read the following information and complete the tasks and questions that follow.
proband
the first affected individual in a family with a genetic disorder who is manifesting the
disease and is diagnosed so
Proband: Anne
Anne is 16 years old and is a junior in high school. She has read some information in the popular press on Marfan
Syndrome and she and her parents are concerned that Anne might have this syndrome. Her general physician
has referred her to the Genetics Counseling Clinic. Anne is 5' 11", and wears contact lenses to correct for myopia
(nearsightedness). She plays on her school's varsity volleyball and basketball teams. NCAA scouts are already
interested in her playing ability and there is a chance she will be offered college scholarships in both sports. Her
armspan:height ratio is 1.08:1. (In one group of 27 adults, this ratio was 1.006 with standard deviation = 0.03.)
The Siblings
David
Age 25, married to Jessica, age 25, one daughter named Kristi, age 3 months. David wears glasses, is 6' 3", has
long fingers and toes, played basketball and ran track in high school, had some knee problems that developed
during his high school athletic career. Jessica is 5' 8", no glasses, no health complaints other than occasional
migraine headaches. She and David had one miscarried pregnancy in the first trimester before the birth of Kristi.
Cheryl
Age 14, 5' 9", no glasses, has a slight case of scoliosis. She was born with club feet which responded well to
corrective treatment.
The Parents
Mary
Age 47, 5' 7", wears glasses, has hay fever. Has been diagnosed with carpal tunnel syndrome and mild diabetes.
Had two miscarriages in addition to her three children.
Peter
Age 49, 6' 1", wears glasses, concave chest, high blood pressure, partial lens dislocation in left eye, long fingers
and toes. Has complained about chronic tennis elbow.
The Aunts and Uncles
Mary's Siblings
Dorothy
Age 46, wears glasses, 5' 3", no major health problems. Has had an ovarian fibroid tumor removed at age 40.
Married and has 4 children.
Ellen
Age 50, 5' 5", high cholesterol, has been diagnosed with irritable bowel syndrome. Unmarried, no children.
Eric
Age 51, 6' 1", wears reading glasses, has recurrent back problems from a car accident, suffers from exerciseinduced asthma. Is married and has two children from his first marriage and three from his second.
Peter's Siblings
Frank
Age 55, 6' 4", wears glasses, slight hearing loss in one ear. Was treated for alcoholism, is a heavy smoker and
has developed a chronic cough. Divorced, the father of 2 children.
Alice
Age 56, 5'7", wears glasses, arthritis in left shoulder. Married, has one daughter and a son who was born with
cerebral palsy.
John
Deceased, heart attack at age 46, 6'2", had dislocated lens in right eye. He and his wife had three children. Their
youngest lives with his wife, who is still living, as she is slightly mentally retarded.
Larry
Age 58, 6'3", no glasses, high blood pressure. Divorced twice, lives alone now. Had two children by his first
marriage and one by his second. Is a heavy drinker.
Grandparents
Anne's Maternal Grandparents
Evelyn
Died at age 76 of stroke, 5'4", arthritis in hands and feet, wore reading glasses. Was said to have had as many as
5 miscarriages.
William
Age 81, no glasses, 5'10", no major health problems. Has a slight limp due to a bad right knee, occasional rashes,
and hemorrhoids.
Anne's Paternal Grandparents
Gloria
Age 86, 5'8", high blood pressure, some knee and ankle problems. Is concerned about her constipation. Wears
glasses for distance and reading.
Charlie
Died at age 44 of a heart attack, severe vision problems, described as long and lanky. Contracted polio at age 26.
Has been wheelchair dependent since his polio treatment.
IB Biology SL1
3.3.3 Marfan Syndrome
After reading the information provided, complete the following tasks and questions on a separate sheet of
paper. Please use complete sentences and show all of your working where appropriate.
1. Construct a pedigree (by hand) of Anne’s family with respect to Marfan Syndrome.
a) Include an appropriate title, the names of each member and label the appropriate generations.
b) Assign possible genotypes to each member of Anne’s family using the following alleles:
M – having Marfan Syndrome
m – not having Marfan Syndrome
c) Neatness counts… use a ruler!
2. Which members of Anne’s family appear to possibly have Marfan Syndrome?
3. For each family member that appears to have Marfan Syndrome, what are the chances their offspring will
have Marfan Syndrome? Include support for your answers.
4. Assume Anne is heterozygous dominant for the Marfan trait. Construct a Punnett Square for a cross
between Anne and a recessive male.
a) What are the possible genotypes of the offspring?
b) What are the possible phenotypes of the offspring?
5. The genetics counseling community ascribes to a belief in non-directive counseling. That is, they feel that
it is their duty to provide all of the information that is available and desired by a family so that they can
make the decisions that are appropriate to them based on their own cultural, moral, religious, etc. beliefs.
The genetic counseling community cringe when people have the misconception that what they do is to tell
people what decisions to make and what course of action to take.
a) What are the ethical and social issues involved in this particular case for Anne and her parents?
b) Assuming you are part of a genetics counseling team, what information would you provide to
Anne and her family?