Genetic Disorder

Genetic disorders are health conditions caused by changes in an individual’s hereditary material (DNA). These changes may manifest as mutations in a single gene, the combined effect of multiple genes, or chromosomal abnormalities. Genetic disorders can be inherited directly through genetic transmission or may arise from new mutations. These disorders can affect a wide range of conditions, from neuropsychiatric illnesses and metabolic syndromes to developmental delays and behavioral disturbances.

Genetically Based Psychiatric Disorders

• Autism Spectrum Disorder (ASD): Genetic studies have shown that autism is a highly heritable and heterogeneous disorder. Concordance rates among monozygotic twins range from 60 to 90 percent, while rates among dizygotic twins are significantly lower. It has also been reported that siblings of individuals with autism have a 30 to 150 times higher risk of developing the disorder. Significant genetic variations have been identified in regions such as 15q11-q13, 7q, and the X chromosome.

• Attention-Deficit/Hyperactivity Disorder (ADHD): Genetic factors play a major role in the etiology of ADHD. Heritability has been estimated at 76 percent. Twin and family studies have demonstrated substantial genetic contributions to the inattention and impulsivity components of the disorder. Several candidate genes associated with dopaminergic, adrenergic, and serotonergic systems have been identified, including DRD4, DAT1, and COMT.

• Bipolar Disorder: The genetic basis of bipolar disorder is supported by twin and family studies conducted in both adults and children and adolescents. Individuals with a family history of bipolar disorder have a 5 to 10 times higher risk of developing the illness. Genetic susceptibility is particularly linked to genes involved in mood-regulating systems.

• Eating Disorders: Numerous studies have demonstrated a genetic basis for eating disorders such as anorexia nervosa and bulimia nervosa. Family and twin studies have shown that these disorders occur more frequently among first-degree relatives. In anorexia nervosa, the genetic influence is particularly pronounced in the restrictive subtype, with concordance rates among monozygotic twins reaching up to 56 to 66 percent.

Characteristics of Genetic Disorders and Common Genetic Mechanisms

Most genetic disorders are multifactorial, arising from the interaction of inherited and environmental factors. The genetic basis of these disorders may involve the following mechanisms:

• Mendelian (single-gene) disorders: Diseases inherited according to Mendelian patterns (e.g., phenylketonuria).
• Chromosomal abnormalities: Result from numerical or structural changes in chromosomes (e.g., Down syndrome, Fragile X syndrome).
• Polygenic disorders: Disorders caused by the interaction of multiple genes (e.g., autism, ADHD, eating disorders).
• Epigenetic modifications: Heritable regulatory mechanisms that affect gene activation or expression levels without altering the DNA sequence.

Methods Used in Genetic Research

• Twin studies: Compare concordance rates between monozygotic and dizygotic twins to assess the impact of genetic transmission.
• Adoption studies: Help distinguish between genetic and environmental influences.
• Familial studies: Used to identify familial clustering of disease and determine inheritance patterns.
• Molecular genetic studies: Employ candidate gene analysis, genome-wide scans, and linkage analysis to identify gene regions associated with disease.

Genetic disorders underlie many biological and psychiatric conditions and play a significant role in individual differences. Twin, adoption, and molecular-level studies have contributed to a deeper understanding of the causes of genetically based illnesses. Advances in this field are opening new possibilities for early diagnosis, personalized treatment, and preventive interventions.