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CHAPTER 6: Developmental Genetics
Case 1
A 2-year-old child is referred to geneticists because of a large head circumference above the 97th centile, although it is growing parallel to the centile lines. The parents would like to have another child and are asking about the recurrence risk. The cerebral ventricles are dilated and there has been much discussion with the neurosurgeons about possible ventriculoperitoneal shunting. On taking a full family history, it emerges that the paternal grandmother is under review by dermatologists for skin lesions, some of which have been removed, and a paternal uncle has had some teeth cysts removed by a hospital dentist.
Case 2
A 4-year-old girl is brought to a pediatrician because of behavioral difficulties, including problems with potty training. The pediatrician decides to test the child’s chromosomes because he has previously seen a case of 47,XXX (triple X) syndrome in which the girl had oppositional behavior. Somewhat to his surprise the chromosome result is 47,XY—i.e., the ‘girl’ is genetically ‘male’.
CHAPTER 7: Patterns of Inheritance
A 34-year-old man has developed some spasticity of his legs in the past few years and his family has noted some memory problems and alteration in behavior. He has very brisk peripheral reflexes. He is seen with his mother in the genetic clinic and she is found to have significantly brisk peripheral reflexes on examination but has no health complaints. It emerges that her own father probably had problems similar to her son’s in his thirties, but he was killed in the war.
A couple has a child who suffers a number of bone fractures during early childhood after minor trauma and is told that this is probably a mild form of osteogenesis imperfecta. The parents did not suffer childhood fractures themselves, and when they have another child who also develops fractures they are told the inheritance is autosomal recessive. This includes an explanation that the affected children should not see the condition occur in their offspring in the future.
CHAPTER 8: Population and Mathematical Genetics
The incidence of a certain autosomal recessive disorder in population A is well established at approximately 1 in 10,000, whereas in population B the incidence of the same disorder is much higher at approximately 1 in 900. A man from the first population group and a woman from the second population group are planning to marry and start a family. Being aware of the relatively high incidence of the disorder in population B, they seek genetic counseling.
Neurofibromatosis type 1 is a relatively common mendelian condition. In a population survey of 50,000 people in one town, 12 cases are identified, of which 8 all belong to one large affected family.
CHAPTER 9: Polygenic and Multifactorial Inheritance
A 16-year-old requests oral contraceptives from her general practitioner. On taking a family history, it emerges that her mother had a deep vein thrombosis at the age of 40 years and died after a pulmonary embolism at age 55 years. There is no other relevant family history.
A 35-year-old woman is diagnosed with diabetes and started on insulin treatment. She and her 29-year-old brother were adopted and have no contact with their birth parents. Her brother has no symptoms of hyperglycemia. Both have normal hearing and no other significant findings.
CHAPTER 10: Hemoglobin and the Hemoglobinopathies
A Chinese couple residing in the United Kingdom has had two pregnancies and the outcome in both was a stillborn edematous baby (hydrops fetalis). These pregnancies occurred when they lived in Asia and they have no living children. They seek some genetic advice about the chances of this happening again, but no medical records are available for the pregnancies.
A young adolescent whose parents are of West Indian origin is admitted from accident and emergency after presenting with severe abdominal pain and some fever. An acute abdomen is suspected and the patient undergoes laparotomy for possible appendicitis. However, no surgical pathology is identified. Subsequently the urine appears dark.
CHAPTER 11: Biochemical Genetics
A 2-year-old boy, who has a baby sister age 4 months, is admitted to hospital with a vomiting illness and drowsiness. Despite his vomiting symptoms improving quite quickly with intravenous fluid support, his blood glucose remains low and intravenous fluids are required longer than might normally be expected. The parents say that something like this happened before, although he recovered without seeing a doctor.
Emerys Elements of Medical Genetics
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