Patient B Records

Patient B comes in referred to us by a physician. He experiences breathlessness and erratic heartbeat. He is 35 years old and a dwarf.

Patient B's Chart:

Results from Auscultation Exam

This is a difficult sound to diagnose for the uninitiated. The main thing that is obvious is that the first and the second sounds (the "lub" and the "dub") are not single snapping sounds, but occur as paired smaller sounds. The sounds are said to be "split" in this condition. This may be hard to hear, but the graphic representation shows this well.

With just this evidence alone, it is difficult to make a diagnosis, but with later evidence, you will be able to determine that this is partly due to an excessive blood flow into the right ventricle during diastole.

Results from Echocardiography Exam

The echocardiogram shows that the wall between the right and left atria is completely missing in this patient.

This is a severe form of congenital atrial septal defect. The missing wall allows blood reaching the left atrium to cross back to the right side and be pumped through the lungs again, overloading the right heart and making the lungs congested with too much blood.

Another consequence of the mixing wall is the equalization of pressure in the atrium. Normally, the left atrium (part of the systemic circulation) is at a higher pressure than the right atrium (part of the pulmonary circulation). Without the wall, what used to be the right atrium becomes more pressurized than is normal, and excessive blood will flow into the right ventricle during diastole. With more blood to pump, the pumping action of the right ventricle is prolonged and no longer in synchrony with the left ventricle. The resulting different timings of the valve closures can be heard as "split" sounds.

Results from Pedigree Exam

If this trait were dominant, one would expect to see affected individuals in at least one of the parents and in about half of the children. Clearly this is not the case. Yet, the patient has a niece (III/4) who is affected. This pattern of inheritance is consistent with autosomal recessive traits. The patient (and the affected niece) is homozygous with respect to this recessive mutation, while both parents (I/1 and I/2) as well as the younger brother (II/5) and sister-in-law (II/6) are heterozygous carriers.