Genetic Syndrome

Aka: Genetic Syndrome, Hereditary Disease, Congenital Abnormality, Congenital Anomaly, Genetics, Gene, Chromosome, Genotype, Phenotype, Allele, Homozygote, Homozygous, Heterozygote, Heterozygous, Genetic Polymorphism, Autosomal Recessive, Autosomal Dominant, Genetic Test, Genetic Counseling

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II. Definitions

  1. Gene
    1. Core functional and physical unit of heredity, most forming a blueprint for Protein construction
    2. Each gene is encoded by a DNA segment, located in a specific position on a specific Chromosome
  2. Chromosome
    1. One of 23 pairs (46 total) of long DNA strands that are densely packaged into chromatin
    2. Each Chromosome houses 200-2000 genes (except the Y Chromosome which has only 50 genes)
  3. Allele
    1. Two Alleles (one from each parent) are inherited for each gene
  4. Homozygous
    1. For a given gene, the two inherited Alleles are the same
  5. Heterozygous
    1. For a given gene, the two inherited Alleles are different
  6. Genotype
    1. Genetic makeup of an individual (their collection of Alleles)
  7. Phenotype
    1. Genetic (Allele) expression resulting in observable characteristics or traits of an individual
  8. Genetic Polymorphism
    1. Natural variation in DNA, genes or Chromosomes
    2. Single Nucleotide polymorphism refers to gene variation in a single DNA base pair
  9. Autosomal Recessive Inheritance
    1. Conditions that manifest only if both Alleles of a gene mutation are inherited
  10. Autosomal Dominant Inheritance
    1. Conditions that manifests even if only one Allele of a gene mutation is inherited

III. Causes: Early presentation (examples)

  1. Inborn Errors of Metabolism
  2. Down Syndrome
  3. Neurofibromatosis
  4. Tay-Sachs Disease

IV. Causes: Delayed presentation (examples)

  1. Marfan Syndrome
  2. Noonan Syndrome
  3. BRCA
  4. Parkinson Disease
  5. Alzheimer Disease
  6. Charcot-Marie-Tooth Disease
  7. Huntington Chorea

V. Exam: Congenital malformations (examples)

  1. Inner Epicanthal Folds
  2. Altered interpupillary distance
  3. Asymmetric limb size
  4. Hypopigmentation (hair, skin)
  5. Coloboma
  6. Tooth anomalies (e.g. single Maxillary central incisor)
  7. Cafe Au Lait spots
  8. Digit anomalies
    1. Syndactyly (fused digits)
    2. Tapered digits
    3. Clinodactyly (curved digits)
    4. Arachnodactyly (long, slender fingers)

VI. Precautions

  1. Home Genetic Tests (e.g. 23andMe)
    1. Patients mail in a cheek swab sample for DNA analysis
    2. Tests only a subset of available Genetic Tests at a cost of several hundred dollars
    3. Risk of both False Positives and false reassurance when testing is incomplete
    4. Genetic Counseling is preferred for test interpretation and test selection based on patient history
    5. (2018) Presc Lett 25(7): 41

VII. Resources

  1. AAP Diagnosis of common Genetic Syndromes
    1. http://www2.aap.org/visit/cmte18.htm
  2. Genetics - NIH
    1. http://ghr.nlm.nih.gov/
  3. American College of Medical Genetics
    1. http://www.acmg.net

VIII. References

  1. Solomon (2012) Am Fam Physician 86(9): 826-33 [PubMed]

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