At age 16, Peter visits his family doctor for the first time because of macroscopic haematuria. He’s also worried about the fact his abdomen keeps growing in size. His blood pressure is 150/110 mm Hg and the abdominal ultrasound shows multiple cysts over both kidneys, varying in size. His plasma creatinine is 110 micromol/l. He’s successfully treated with antihypertensive drugs. The boy’s mother, who is also hypertensive, turns out to have polycystic kidneys as well. It is concluded that both patients have the autosomal dominant form of polycystic kidney disease. Another ultrasound reveals that Peter’s younger brother – aged 10 – does not have polycystic kidneys. Questions. 1. Does this mean the brother has not been affected with the autosomal dominant form of polycystic kidney disease? 2. After browsing the internet, Peter wonders if further investigations of his brain have to take place in order to detect small vessel anomalies. What would you tell him? 3. What is the chance of Peter’s future children being affected?
the younger brother may also develop plycystic kidney disease, as the disease is autosomal dominant, he probably has cysts but are still undeticted.
Answers. 1. An ultrasound on someone this age is not enough to rule out the possibility of autosomal dominant polycystic kidney disease. A positive test result is to be expected in 11% of 10-year old patients, 33% at age 20 and 43% in 30-year old patients. Therefore, further investigation by using the gene-linkage technique is indicated in this case. Then, there will be almost 100% certainty about whether the brother carries the affected gene. 2. There’s still controversy about the use of cerebral angiography in polycystic kidney disease. Recent studies say that 38% of the patients should have an aneurysm. Obviously, the chance of an aneurysm rupturing increases with the aneurysm’s size, so surgery is recommended when the vessel is more than 1 cm in diameter. It is expected that when technology improves, all patients will be screened. At what age, however, remains unclear. 3. Assuming Peter’s wife will not be affected, their children will have a 50% chance of inheriting this form of polycystic kidney disease; if ‘A’ is the affected allele and ‘a’ the unaffected one (making Peter ‘Aa’ and his wife ‘aa’), then their offspring will either be ‘Aa2’, ‘Aa3’, ‘a1a2’ or ‘a1a3’ (Aa1 x a2a3). Two out of four have the dominant disease bearing allele, so 50% it is. It should also be mentioned that the presence of the condition can be confirmed with prenatal diagnostics. Literature. ’Klinische nefrologie’ (De Jong et al.) (4th edition); a Dutch medical book on nephrology.
