Genetic Diagnosis for Inherited Diseases
What are inherited diseases?
Inherited diseases are those caused by a gene mutation or chromosomal change that is passed from parent to child during the reproductive process.
This DNA change may be passed in one of several different types of genetic inheritance –
Autosomal recessive: Autosomal recessive inheritance means an affected individual receives one copy of a mutated gene from each of their parents, giving them two copies of a mutated gene. Parents, who carry only one copy of the gene mutation will not generally show any symptoms, but have a 25% chance of passing the copies of the gene mutations onto each of their children. Cystic fibrosis is one of the most common inherited diseases due to this mode of inheritance.
Autosomal dominant: In the case of autosomal dominant inheritance just one parent is the carrier of the gene mutation, and they have a 50% chance of passing it onto each of their children. Syndromes inherited in an autosomal dominant inheritance are caused by just one copy of the gene mutation. Larsen syndrome is a disease inherited in this way.
X-linked recessive: Syndromes inherited in an X-linked recessive pattern generally only affect males. Males only have one X chromosome, and so one copy of a gene mutation on it causes the syndrome. Females, with two X chromosomes, only one of which will be mutated, are not likely to be affected. Fragile X syndrome is one of the most well known syndromes inherited in this way.
X-linked dominant: Syndromes inherited in an X-linked dominant pattern, a mutation in just one of the copies of the gene, causes the syndrome. This can be in one of the female X chromosomes, and in the one X chromosomes males have. Males tend to have more severe symptoms than females. Rett syndrome is one example of a rare disease inherited due to this mode.
Not all genetic syndromes are inherited. They may be the result of a spontaneous, unknown, or new mutation. Some mutations might also be triggered by environmental factors. This means that some rare disease may be classed as an inherited disease in some cases, but not in others.
Genetic diagnosis for inherited diseases
A rare disease diagnosis may be triggered if the parents of a child are known to be carriers for a specific gene mutation. It might also be a process that parents-to-be choose to undergo before starting a family, to understand both their own genetic health and the potential risk of their future children developing or carrying the gene mutation for a rare disease.
Genetic diagnosis for inherited disease will also be recommended for an individual with a family medical history of symptoms that might relate to a rare disease, or a pattern of specific symptoms within a family that might point to a genetic syndrome.
Misdiagnosis & diagnosis accuracy
Misdiagnosis amongst inherited disease patients is still much too high. The rate of misdiagnosis is believed to be as high as 73%. This suggests that there is a real issue with accuracy in the diagnosis of rare disease. This inaccuracy delays treatment, support, and the right intervention for individuals with an inherited disease, and ultimately impacts on positive life outcomes also. Genetic diagnosis for inherited diseases has a long way to go in terms of improving accuracy rates, and in ensuring patients are supported and treated properly both in the short and long term management of their condition and care.
A delayed diagnosis is a very real challenge for many inherited disease patients. On average patients wait 4 years for a diagnosis, due to misdiagnosis, limited access to targeted genetic testing, and limited access to genetic counseling services. Over 50% of patients do not receive an accurate diagnosis.
A delayed diagnosis has similar consequences as a misdiagnosis in terms of what it means for an inherited disease patient. Delayed treatment, delayed support, and delayed care are the very real consequences.
Delayed access to testing & support
Limited and delayed access to genetic testing and support, through the services of genetic counseling, are also two of the major challenges facing genetic diagnosis for inherited disease.
Genetic counselors, through genetic counseling, provide valuable information and support to rare disease patients about their syndrome, symptoms, and options for testing. This knowledge and experience helps lead patients to a more accurate diagnosis, and a faster one too. This in turn means more timely access to the care and support that improves long term life outcomes for patients with an inherited disease.
- Increase awareness about rare disease, and advocate for greater research and funding for inherited diseases
- Improve access to crucial services that improve the accuracy of a diagnosis, specifically genetic counseling
- Increase understanding about how rare diseases are inherited and caused, the importance of carrier screening
Understanding the current challenges facing genetic diagnosis for inherited diseases, is the first step, in understanding how to improve the entire diagnostic process for rare disease patients.