There are a few disorders that occur only in men, but are always inherited through their mothers. These include hemophilia, red-green colour blindness and two forms of muscular dystrophy. Of course, there are many more defects that can be inherited. Each chromosome inherited from a parent carries many thousands of genes or units of genetic information, and if any one of these genes is faulty a defect can occur.
However, these few disorders such as hemophilia are passed on in the odd way because they are linked with the X chromosome. This is one of the chromosomes that determine gender. Both men and women have X chromosomes in which one of these genes is faulty, but whenever the defective chromosome is matched by another normal X chromosome, then the defect will not appear. The normal chromosome guarantees the correct function such as colour vision, which means the normal gene is dominant.
Only a healthy chromosome from the male parent masks the defective chromosome from the female parent. Thus, a father with the defective gene cannot pass it on to his son at all, because to them he contributes only his Y chromosome. But a mother can pass it onto her sons, because to them she contributes their X chromosome, which may be defective, and their other Y chromosome, will not mask it, because it does not have a gene responsible for the defective function.
The only way in which a woman can show signs of one of these defects is if she has inherited defective X chromosomes from both sides of the family. This is very unlikely, but does happen rather more often in the case of colour blindness. A woman who does not show signs of the disorder, but can pass it on is called a carrier. Only chance decides whether or not any one of her children inherits the defective X chromosome; the child can equally inherit the healthy one. So if a carrier becomes pregnant, there is a one in four chance of her having a normal son or daughter, an affected son or daughter, or a carrier daughter.
If a woman is found to be a carrier, there is a risk not only to her own subsequent children but also to those of her female relatives on the maternal side, because they may also have inherited the defective gene. If no previous family history is discovered after careful check, it is likely to be an isolated mutation in either mother or child. If in the mother, she can still pass it on to subsequent children.
Let us examine closely some of the male inherited conditions:
Haemophilia
This disorder is characterised by uncontrollable bleeding, even after slight wounds. It is caused by a deficiency of one of the elements needed to make the blood clot.
Symptoms
In mild cases, the disorder may remain undiscovered until revealed by some incident such as loss of a tooth. In severe cases, it will be obvious soon after birth. There is often persistent blood flow from any cut even a minor one or in any bruise. Without special treatment this may continue for hours or even days, despite normal attempts to stop it. Even when the flow does finally stop, it may recur soon after.
The real danger, however, is from internal bleeding. Superficial cuts and scratches are not threatening unless the mucous membrane is involved, and deep cuts do not kill unless a major vein or artery is involved. But bleeding in soft tissues such as the kidney is serious, and bleeding in large joints can eventually cripple them. Both these can occur spontaneously in severe cases. The symptoms may decline with age and at any age there may be periods free from trouble.
Treating haemophilia
The haemophiliac has to take special care in all he does and in severe cases his sphere of activity is drastically curtailed. Any sports involving body contact or danger of injury must be avoided though he can still swim, run and so forth. Haemophiliacs often wear warning tags, in case they are involved in accidents. If bleeding does occur the missing factor is injected intravenously to help clotting. This is also done if an operation or tooth extraction is necessary.
Muscular dystrophy
This is a disease in which the muscles waste away. Muscle tissue does not replace itself, and slowly gives way to fibrous tissue and fat. It may be due to absence or excess of protein or presence of abnormal protein. There are several forms of the disease, all of which are hereditary, but two are sex-linked-inherited almost only by men, and through female carriers. The carriers themselves may have slight muscle weakness, but are usually apparently normal.
Duchenne type
This is the most common and most severe form of muscular dystrophy. Half of those with muscular dystrophy are boys with the Duchenne type. The disease is invariably fatal and most of those with it die by the time they are 25. The first symptoms develop between the age of two and five. Walking is often clumsy and running is poor with frequent falls. Climbing stairs and getting up after falls becomes difficult.
Weakness begins with certain muscles of the shoulders, upper arms, and thighs. Diagnosis is often done by measuring enzymes in the blood serum and examining small muscle samples under a microscope. If muscular dystrophy is suspected in a family, these tests can also diagnose it within a few days of a child’s birth.
There is no cure or effective drug treatment, but exercise and muscle stretching can slightly slow down the progress of the disease, but eventually, usually between the age f eight and 11, the child has to use a wheelchair. The spine curves, muscle weakness spreads, eventually affecting even eating and drinking and muscle contraction distorts limb positions. Finally respiratory and heart muscles are involved and death occurs, usually between 16 and 25. There are tests that help detect if a woman is a carrier though none can show when she isn’t.
Becker type
This is almost similar to the Duchene in the muscles affected and pattern of inheritance, but it is often rare and comes much later in life, is slower and milder. Patients can usually still walk in their thirties and often into middle age.
Published in May 2013
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