We inherit from our parents not only external features, such as the color of hair or eyes, but also a number of diseases or a greater predisposition to them. Genetic diseases linked to the X chromosome constitute a fairly large group, the symptoms of which are often revealed only in women or only in men. Why is this happening? What are the most common gender-linked diseases?
Gender-linked inheritance
The inheritance of traits is governed by the laws of genetics, which are better known to us thanks to Mendel’s laws (the famous research on pea crossing). Sex determines the presence of a pair of XX (female) or XY (male) chromosomes. A woman in her “genetic suit” has two X chromosomes (one from the father, one from the mother), while the man has only one X chromosome.
X-linked genetic diseases can be inherited either recessively or predominantly. Recessive disorder occurs mainly in men, while heterozygous women are carriers of the defective gene, but do not show symptoms of the disease. A genetic disease can occur in a woman when both X chromosomes in their genetic material contain a mutated gene.
Based on these principles:
- the man cannot transfer the disease to his son,
- women with sex-linked diseases most often inherited two faulty genes from their father and mother,
- if the disease is recessive, the sick man has healthy offspring of both sexes,
- if the disease is dominant, the symptoms of the disease will appear in all daughters of the sick man,
- female carriers are healthy, but pass the defective gene to half of their offspring of both sexes.
As genetic diseases are currently incurable, treatments are aimed at alleviating symptoms and improving the patient’s quality of life.
10 sex-linked genetic diseases
Hemophilia
It is a genetic blood disorder that belongs to bleeding disorders. It is inherited recessively, which means that only males get sick, while females are asymptomatic carriers.
The underlying cause of the disease is the lack or deficiency of blood clotting factors. This means that in the event of damage to a blood vessel (e.g. nose hemorrhage), the formation of a clot becomes difficult, which under physiological conditions is formed by the cooperation of coagulation factors, morphotic elements and thrombocytes. Thus, the bleeding time is significantly extended.
Depending on the clotting factor, the following are distinguished:
- haemophilia A (factor VIII deficiency),
- haemophilia B (factor IX deficiency),
- haemophilia C (factor XI deficiency).
The first symptoms of the disease appear already in childhood. The severity of symptoms depends on the level of deficiency of a given clotting factor.
Due to new treatment options, the everyday life of patients with hemophilia may look different than a dozen or so years ago. Thanks to the therapy, patients have a chance to lead a normal, active life, fulfilling themselves both professionally and privately. Clotting factor concentrates were a breakthrough in the treatment of hemophilia, and new methods of therapy, such as non-substitutable treatment, can be called a real revolution.
Color blindness (color blindness)
Color blindness, commonly known as color blindness, is an X-linked recessive genetic disease. It occurs more frequently in men than in women. The disease is characterized by an inability to perceive red and green (and to a lesser extent yellow and orange) colors correctly.
There are three types of color blindness:
- Monochromatism – this is a complete inability to distinguish colors. It is the rarest of all types of color blindness, and a person with this condition sees the world in shades of black and white.
- Dichromatism – occurs due to the lack of a photoreceptor. The patient is unable to distinguish between red and green.
- Trichromatism – is characterized by a decrease in the sensitivity of suppositories located on the retina, as a result of which the organ of sight does not perceive fully saturated colors.
Color blindness can also develop as a result of diseases of the retina or the visual tract, as well as a consequence of the chronic use of certain psychoactive drugs or the aging of the body.
One of the methods of vision correction are specially designed glasses that adapt to the defect and allow you to see expressive and fully saturated colors.
Duchenne muscular dystrophy
X-linked recessive inheritance. Only males suffer from it. The mutation concerns genes encoding muscle proteins (dystrophins) that play important building functions. Their absence disrupts the work of large muscle groups, including those that form not only the locomotor system, but also the heart. Due to the lack of dystrophins, necrosis and replacement of muscle tissue with fibrous tissue occurs.
The first symptoms of Duchenne muscular dystrophy appear in young boys. Sick children are less physically agile, have problems with learning to walk, often lean on their hands and fall over. Most often, at the age of 12, patients are confined to a wheelchair. Cases of death are generally respiratory muscle damage or advanced cardiomyopathy. In the mildest version of the disease, a person with muscular dystrophy may live up to around 50 years of age.
Fragile X syndrome (FRA X)
The cause of the development of the fragile X chromosome syndrome is a dynamic mutation in the FMR1 gene located on the X chromosome. The symptoms of the disease appear mainly in men. With this condition, a phenomenon known as the Sherman Paradox is observed. This means that the greater the number of generations in which the gene mutation has been passed on is the higher the probability of the appearance of symptoms.
A person with a mutation in the FMR1 gene is distinguished by protruding auricles, delayed speech development and intellectual disability (moderate or severe). Often these symptoms are accompanied by: hyperactivity, concentration disorders and some features of autism.
Rett syndrome
Rett syndrome only affects women. The genetic mutation of the MECP2 gene located on the X chromosome is lethal for most men and ends in death already at the stage of fetal development. The symptoms of the disease appear suddenly and progress very dynamically, leading to significant intellectual and motor impairment.
Initially, a girl with the disease develops properly. The first and worrying sign may be the gradual loss of power over free movements. Epilepsy, difficulty walking and performing simple activities may also develop over time. The child also begins to show cognitive problems. In the early stages of development, Rett syndrome is confused with early childhood autism.
Alport team
This congenital disease occurs mainly in boys and leads to severe kidney failure accompanied by visual and hearing impairment. The mutation affects several COL4A3-6 genes located on the X chromosome. Alport syndrome may be inherited in a dominant or recessive manner, and the consequence of such inheritance is an abnormal structure of type IV collagen in the eye, ear and kidneys.
Symptoms of Alporta syndrome include:
- proteinuria or hematuria,
- polyneuropathy,
- hypertension,
- gradual deafness starting already in childhood,
- posterior subcapsular cataract.
The disease usually does not appear until after the age of 10. The earlier symptoms are not specific, such as frequent colds, problems with concentration, lack of appetite and poor body structure. Rapid diagnosis allows to some extent to inhibit the deteriorating damage to the kidneys, eyes and hearing.
Choroba Charcota-Mariego-Tootha
It is one of the groups of genetic diseases inherited in an autosomal dominant or recessive way, the symptoms of which are manifested already in childhood. The exact clinical picture depends on the type of mutation in one of several genes.
Motor-sensory neuropathy belongs to a heterogeneous group of peripheral nerve diseases. Based on differences in nerve conduction velocity, Charcot-Marie-Tooth disease is classified into the following groups:
- CMT1 – demyelinating form with slowing of nerve conduction velocity,
- CMT2 – axonal form with normal or slightly decreased nerve conduction velocity.
The disease progresses slowly and slowly affects subsequent groups of muscles and nerves. Common symptoms include foot deformities, impaired gait and posture, as well as sensory disturbances and muscular atrophy in the distal parts of the limbs.
Menkes disease
Menkes Disease is otherwise known as Curly Hair Disease. It is a relatively rare genetic disease, the essence of which is the disturbance of copper metabolism in the body. The disease mainly affects the male sex, and women are carriers of the defective ATP7A gene. As a result of the mutation, the absorption of copper in the intestines and its transport to the central nervous system are reduced.
Symptoms of Menkes’ disease result from a significant copper deficiency and include:
- psychomotor development delay,
- reduction of muscle tone,
- seizures
- bladder diverticula,
- flabby skin,
- curly hair with a tendency to fall out and break,
- enlargement of the bone structure, leading to numerous fractures.
Menkes’ disease appears most frequently between the ages of 2 and 4 months. The newborn may have difficulty feeding, breathing problems and a low body temperature. Diagnosis is based on clinical symptoms and the presence of biochemical markers.
Coffin Lowry’s syndrome
It is a rare X-linked genetic disease that is inherited in an autosomal dominant fashion. Coffin Lowry syndrome arises as a result of a mutation in the RSK2 gene encoding a signaling protein.
Congenital defects are manifested primarily in the form of mental retardation and general developmental delay. Children are distinguished by an atypical skeleton structure and facial dysmorphism (wide nose and mouth, large ears, prominent forehead, wide eyebrows, eye hypertelorism).
Barth’s team
It is a genetically determined sex-linked metabolic disease. Symptoms already appear in young boys, while girls are asymptomatic carriers. The mutation concerns the tafazine gene (TAZ), which contributes to an increased concentration of 3-methylglutaconic acid in the urine.
Barth syndrome is characterized by, inter alia, Dilated cardiomyopathy, low and delayed growth, impaired mitochondrial function, neutropenia, low blood cholesterol, as well as facial dysmorphia (prominent frontal tumors, deeply set eyeballs, prominent cheeks).
As people age, there are more serious problems with recurring infections, swelling and cardiovascular failure. Thus, the risk of stroke and even sudden cardiac arrest increases. Children with Barth syndrome also experience learning difficulties due to impairment of cognitive functions, concentration and visual-spatial perception