Genetic counseling involves the assessment and interpretation of genetic information from individuals, families, or communities by healthcare professionals or genetic counseling specialists. This process includes providing appropriate medical advice and support. The specific tasks include helping patients and their family members document family and medical histories, selecting appropriate genetic testing plans, interpreting genetic test results, obtaining detailed clinical phenotypes, analyzing genetic mechanisms, informing patients of possible prognoses and treatment options, assessing recurrence risks in future generations, and developing reproductive plans, including prenatal diagnosis or preimplantation genetic testing.
Target Groups
The target groups for genetic counseling are high-risk populations for hereditary diseases, which include:
- Couples or individuals with a family history of genetic disorders, birth defects, unexplained epilepsy, intellectual disabilities, tumors, or other conditions closely related to genetic factors, or couples who have previously had a child with a congenital defect.
- Individuals with intellectual disabilities or birth defects, or couples in which one partner has such conditions.
- Couples with a history of recurrent pregnancy loss or stillbirths of unknown cause.
- Couples who have been exposed to adverse environmental factors during pregnancy or who have chronic illnesses.
- Individuals with abnormalities detected during routine screenings or common genetic disease screening.
- Others in need of counseling, including couples with infertility despite years of marriage, advanced maternal age (women aged 35 or older), or consanguineous marriages.
Types
Genetic counseling is categorized based on its subject matter and target groups. The main categories include premarital counseling, preconception counseling, prenatal counseling, pediatric genetic disease counseling, cancer genetic counseling, and other specialized counseling (such as for neurological genetic disorders or hematological disorders).
Principles
Certain ethical and moral principles must be adhered to during the genetic counseling process.
Principle of Autonomy
The wishes and decisions of the individual seeking counseling should be respected. Any choices made, particularly regarding pregnancy outcomes and genetic testing, must not be influenced by coercion or undue pressure. The differing attitudes and viewpoints of individuals due to their religious beliefs and social backgrounds must also be acknowledged and respected.
Principle of Informed Consent
During genetic counseling, individuals must have a clear understanding of all matters related to their own health, the health risks of family members, potential uncertain genetic findings without clear clinical significance, and the advantages and disadvantages of various testing and treatment plans. They must be able to make fully-informed and independent medical decisions. For genetic testing results, especially findings outside the primary testing scope (such as late-onset genetic diseases or cancer predispositions), individuals have the right to be informed or to decline disclosure. Prior to such testing, genetic counseling should explore the individuals' attitude and capacity to handle additional findings, and whether or not to disclose the results should align with their wishes.
Principle of Non-Directive Counseling
There are no universally correct or wrong options in the process of genetic counseling. Healthcare professionals are responsible for providing individuals with a clear understanding of the advantages and disadvantages of different options, rather than choosing on their behalf. Non-directive counseling has been a foundational principle of genetic counseling and is also endorsed by the Expert Advisory Group on Genetic Counseling of the World Health Organization. Physicians may provide medical advice, but individuals and their families retain the right to make decisions.
Principle of Confidentiality and Privacy Protection
Maintaining confidentiality is a professional ethical obligation in genetic counseling. Genetic testing results should not be disclosed to third parties, including employers, insurance companies, or schools, without explicit permission from the individual. Genetic testing may uncover sensitive family information (e.g., non-paternity or inconsistent kinship). Counselors must follow the individual's wishes to protect their privacy.
Principle of Fairness
Ideally, all genetic services, including counseling and testing, should be equally accessible to all individuals who need them.
Content and Basic Process
Genetic counseling is an information-providing service, and its content generally covers the following five aspects:
Understanding the Clinical Phenotype
The counseling process helps patients and their family members understand the clinical symptoms of the disease, such as cognitive impairments or physiological defects.
Explanations of the Genetic Mechanism
Genetic counselors use accessible and understandable language to explain the mechanisms of the disease, specifically the genetic abnormalities leading to its development.
Providing Information on Treatment Options
Information on available treatment options and the prognosis of the disease is provided, so that patients can benefit from a genetic diagnosis. Supportive information on organizations that provide assistance for specific diseases should also be made available.
Counseling on Recurrence Risk
The risk of recurrence of the hereditary disease within the family should be evaluated. Genetic counselors analyze inheritance patterns based on confirmed diagnoses and consider potential variations in genotype and phenotype to assess genetic risks and explain the likelihood of recurrence in the next generation.
Reproductive Planning
Information is provided to assist patients and their families in planning subsequent pregnancies. Recommendations on measures and reproductive options, such as natural conception with targeted prenatal diagnosis, preimplantation genetic testing, sperm or egg donation, etc., are discussed.
Types of Human Genetic Disorders
Human genetic disorders can be categorized into six types: (1) chromosomal disorders, (2) genomic disorders, (3) single-gene disorders, (4) multifactorial (polygenic) disorders, (5) mitochondrial disorders, and (6) somatic cell genetic disorders.
Chromosomal Disorders
Chromosomal disorders are the most common type of genetic condition causing birth defects. Chromosomal abnormalities can be classified into numerical and structural anomalies. Numerical abnormalities include both polyploidies (such as triploidy) and aneuploidies (such as trisomy 21, trisomy 18, trisomy 13, 47,XXX syndrome, or Turner syndrome [45,X]). Structural abnormalities encompass partial deletions, duplications, translocations, inversions, insertions, isochromosomes, and ring chromosomes. There are currently no effective treatments for congenital chromosomal disorders, which underscores the importance of early diagnosis for promoting healthy reproduction and birth outcomes.
Genomic Disorders
Genomic disorders arise from abnormal recombination within genomic DNA, leading to microdeletions, microduplications, or disruptions of gene structure, which are associated with abnormal clinical phenotypes. Microdeletions and microduplications refer to small chromosomal alterations (often smaller than 5Mb) that are difficult to detect using traditional cytogenetic techniques. These disruptions result in genetic syndromes with complex clinical phenotypes, referred to as chromosomal microdeletion and microduplication syndromes.
Single-Gene Disorders
Single-gene disorders, also known as Mendelian disorders, occur due to variations in a single gene or allele. They include diseases that follow classic Mendelian inheritance patterns, such as autosomal dominant disorders, autosomal recessive disorders, as well as X-linked and Y-linked inheritance. Other inheritance patterns associated with single-gene disorders include genomic imprinting, genetic anticipation, uniparental disomy, and pseudoautosomal dominant inheritance. However, it is estimated that less than 1% of single-gene disorders have effective treatments available.
Multifactorial Disorders
Multifactorial disorders are influenced by the combined impact of multiple pathogenic or susceptibility genes along with environmental factors, resulting in complex disease mechanisms that vary across populations. The accumulation of effects from multiple genetic factors may produce significant phenotypic outcomes, referred to as additive effects. Among these genes, certain ones may play a major role and are referred to as major genes, which are particularly valuable for understanding the development, diagnosis, treatment, and prevention of multifactorial diseases. While multifactorial disorders may exhibit a familial predisposition, they do not show the pedigree characteristics typical of single-gene disorders. Common human diseases such as hypertension, atherosclerosis, diabetes, and schizophrenia are classified as multifactorial genetic disorders.
Mitochondrial Disorders
Mitochondrial disorders are caused by abnormalities in mitochondrial DNA (mtDNA). Additionally, certain genes within the nuclear genome (nDNA) encode components related to mitochondrial function, and mutations in these genes may lead to mitochondrial dysfunction. Disorders resulting from nuclear gene mutations follow single-gene inheritance patterns, most commonly autosomal recessive inheritance, and typically manifest at an earlier age. Disorders caused by mtDNA mutations adhere to maternal inheritance patterns and generally show later onset.
Somatic Cell Genetic Disorders
Somatic cell genetic disorders result from mutations in the genes of somatic cells (excluding germ cells). The accumulation of such mutations contributes to disease development. As somatic cell mutations are not heritable, these disorders are not passed down to offspring. The most representative examples of somatic cell genetic disorders are various types of sporadic tumors.