If you look carefully at your family tree, you may notice that certain diseases and conditions seem to follow a gender-specific pattern. There are a number of diseases that are sex-linked, which means these conditions mainly affect family members of one gender and are passed from parent to child.
How Gender-Specific Diseases Are Inherited
Sex-linked conditions and diseases are those that are carried by the X and Y chromosomes, the part of your genome that determines whether you're a male or a female. Males receive an X chromosome from their mother and a Y chromosome from their fathers. Females receive an X chromosome from each parent.
| Offspring Sex || Father (XY) || Mother (XX) |
| Male || Y || X |
| Female || X || X |
LiveScience reports that the X chromosome is much larger than the Y chromosome and, in addition to its role in sex determination, carries 1,098 genes responsible for many different characteristics. The smaller Y chromosome only carries 26 genes.
Male-Specific Genetic Diseases
Because males only have one copy of the X chromosome, many diseases are passed from mother to son. Unless they have two X chromosomes for the disorder, women are usually only mildly affected or are simply carriers of the disease.
Male-pattern baldness, also known as androgenetic alopecia, is a condition that affects both men and women; however, it's far more common in men. According to Genetics Home Reference, in the United States, 35 million men suffer from some level of male pattern baldness. Multiple genes cause androgenetic alopecia, but at least two of them are located on the X chromosome. In females, the second X chromosome offers some protection against baldness, which is why women are less likely to have this condition. There are a number of topical treatments to reduce the symptoms of male-pattern baldness.
Affecting only 1 out of every 50,000 people, Alport Syndrome causes vision and hearing problems and kidney disease. This disease affects both men and women, but because it is carried on the X chromosome, it has a much more serious effect on males. Males frequently experience progressive kidney problems and eventual kidney failure. Females' second X chromosome typically serves to mitigate the negative aspects of this disease. There is no cure for Alport Syndrome, but kidney dialysis and transplant can extend life.
Prostate cancer is another disease that affects men and has a genetic component. According to the National Cancer Institute, about 233,000 men are diagnosed with prostate cancer annually. Of these cases, up to 10% are genetic. There is still a great deal of research underway to identify the genes responsible for this type of cancer and the inheritance pattern that accompanies it. Prostate cancer can vary in severity, and depending on the type and stage, it is treated with surgery, chemotherapy, radiation, hormone therapy, or watchful waiting. In many cases, prostate cancer is treatable.
Duchenne Muscular Dystrophy
Duchenne Muscular Dystrophy affects one out of every 3,600 male babies born each year, according to the National Institute of Health. It involves a defective gene on the X chromosome that is responsible for producing dystrophin, a muscle protein. Females can be carriers of this gene, but because of their second X chromosome, they are almost never affected by the condition. Symptoms include progressive muscle deterioration, learning problems, and eventually, loss of basic functions for life. There is no cure, but treatments like steroids, assistive devices, and amino acid supplements can improve quality of life.
Red-Green Color Blindness
Certain types of color blindness, including defects in red-green color vision, are due to genes on the X chromosome and primarily affect males. In order for a woman to have this condition, she needs to have two defective X chromosomes. According to Genetics Home Reference, eight percent of males of Northern European descent suffer from red-green color blindness, while it only affects 0.5% of women. Men with red-green color blindness have a difficult time identifying different tones of red and green and may see these colors as brown or gray. There is no treatment for this condition.
Hemophilia is a blood clotting disorder that is carried on the X chromosome. According to the Centers for Disease Control and Prevention, about 1 in 5,000 male babies are born with hemophilia each year. Women can be carriers of the gene for hemophilia, but their second X chromosome offers protection against the disease. Hemophilia has different levels of severity, ranging from moderate bleeding problems to bleeding that is more difficult to control and is accompanied by joint issues, and sometimes, heart defects. Treatments can include specialized blood products, home care for injuries, and therapies from hemophilia treatment centers.
Fragile X is a condition that affects both males and females, but males are affected to a greater degree. As the name implies, this disease involves mutations on the X chromosome. According to the National Fragile X Foundation, about 1 in 3,600 males have this condition, which involves distinctive facial features, intellectual disability, and behaviors that can mimic ADHD and autism. About 1 in 250 women and 1 in 800 men carry a "premutation," or the beginnings of the fragile X mutation, on their X chromosome. The mutation can get progressively more severe with each generation, eventually leading to fragile X. Treatment for fragile X involves behavioral therapy and alternative education.
Female-Specific Genetic Diseases
There are fewer female-specific genetic diseases, but these conditions do still exist. According to the National Center for Biotechnology Information, there are two main genetic disorders that are female-specific.
Breast and Ovarian Cancer
According to the National Cancer Institute, certain types of breast and ovarian cancer are highly genetic. Gene mutations on chromosome 17 and chromosome 12 affect the body's ability to repair damage to cells. In many cases, this can lead to genetic coding errors causing uncontrolled cell growth in the breasts and ovaries. These gene mutations pass from parent to child and frequently affect multiple generations of a family. They account for up to 25% of genetic breast cancers and 15% of ovarian cancer cases.
Breast and ovarian cancer are treated according to the stage and type of cancer, and treatments often involve surgery, chemotherapy, hormone therapy, and radiation. Some women choose to be screened for the genetic mutations and have their breasts and ovaries removed as a preventative measure.
Occurring in about 1 in 10,000 female infants, Rett Syndrome typically involves a developmental regression sometime in the first 18 months of life, according to the International Rett Syndrome Foundation. Symptoms include problems with various types of brain function - from emotional and behavioral issues to cognitive challenges. The level of disability varies significantly, and treatment typically involves behavioral therapy and special education. Rett Syndrome results from a mutation on the X chromosome, which a girl can receive from either parent.
Implications for Genealogists
As you research your ancestors, you may encounter some of these disorders. Certain diseases may be listed as the cause of death on death certificates and other public records. Other conditions, like male-pattern baldness, may be evident in old photographs. It's helpful to record as much information as you can about the role of these gender-specific genetic diseases in your family tree. Future generations may even use your work to make medical decisions.