Connie Winslow is deaf. When she was old enough to attend school, she began havi

Question

Connie Winslow is deaf. When she was old enough to attend school, she began having fainting spells that her teachers and parents noticed happened when she became excited. One Christmas, she was so thrilled with her gifts that she immediately fainted. Her parents took her to the emergency room, where the doctors once again told them, there wasn’t a problem. The spells continued and after awhile, Connie began to predict the occurrence of the attacks, telling her parents that her head hurt before she fainted. After checking Connie’s heart, a neurologist finally diagnosed her with long-QT syndrome with deafness, also known as Jervell and Lange-Nielson syndrome (see OMIM 220400). He explained that she has a severe form of syndrome, which is an inherited heartbeat irregularity that can be fatal. Seven different genes can cause long- QT syndrome.   The doctor told them of a case described in the textbook, in 1856: a young girl, called at school to face the headmaster for an infraction, became so agitated that she dropped dead. When the parents were summoned, they were not surprised hey had lost two other children to great excitement.

The Winslows visited a medical geneticist, who discovered that each had a mild heartbeat irregularity that did not produce symptoms. The parents had normal hearing. Connnie’s younger brother was also hearing impaired and suffered night terrors but so far had not fainted during the day. Like Connie, he had the full syndrome. A younger sister was still a baby, and was tested. She did not have either form of the family’s illness; her heartbeat was normal.

Today, Connie and her brother are treated with beta-blocker drugs, and each has a pacemaker to regulate heartbeat. Diagnosing her may also have saved her brother’s life.

Which hereditary concept(s) most likely apply to the condition in this family? Explain using facts given in the case.

How is the inheritance pattern of Jervell and Lange-Nielson syndrome similar to that of familial hypercholesterolemia?

How is it possible that Tina did not inherit either the serious or the asymptomatic from of the illness?

Do the treatments for the condition affect the genotype or the phenotype?

Explanation / Answer

1) Jervell and Lange-Nielson syndrome follows an autosomal recessive pattern of inheritance. In this case both of the parents are carriers, who carry a single disease allele. Connie and her younger brother have inherited the recessive alleles from both parents. Hence they are affected. They each had a probabilty of 1/4 in being affected.

2) Jervell and Lange-Nielson syndrome and familial hypercholesterolemia are both autosomal disorders. But familial hypercholesterolemia follows a autosomal dominant pattern of inheritance, in which presence of one disease allele is sufficient express the phenotype of the disease.

3) If Tina is the younger sister who is a baby, then she is not expressing the phenotype because she is not a carrier or an affected individual. She has inherited normal alleles from both of her parents. Her chance of being normal was also 1/4 in this autosomal recessive disease.

4) The treatments affect the phenotype of the affected individuals. Abnormal heart beat is the phenotype produced by the abnormal genotype. The beta blocker drugs slow down the heart beat and the pacemaker controls the heart beat.

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