Back Topic Index - Medical Genetics Medical Genetics Home Overview of Birth Defects Chromosome Abnormalities Overview of Chromosome Abnormalities Types of Chromosome Abnormalities Numerical Abnormalities: Overview of Trisomies and Monosomies Down Syndrome (Trisomy 21) Trisomy 18 & 13 Turner Syndrome Structural Abnormalities: Deletions (Cri du Chat) and Duplications (Pallister Killian) Translocations Translocation Down Syndrome Other Arrangements: Rings and Inversions Mosaicism Mosaic Down Syndrome How Chromosome Abnormalities Happen: Meiosis, Mitosis, Maternal Age, Environment Chance a Chromosome Abnormality Will Occur Again: Numerical, Structural (Inherited and De Novo), Mosaicism Single Gene Defects Overview of Single Gene Defects Autosomal Dominant: Marfan Syndrome Autosomal Recessive: Cystic Fibrosis, Sickle Cell Anemia, Tay Sachs Disease X-linked Recessive: Red-Green Color Blindness, Hemophilia A X-linked Dominant: Incontinentia Pigmenti The Difference Between a Chromosome Abnormality and a Single Gene Defect Multifactorial Inheritance Teratogens Teratogens Overview Examples of Teratogens Fetal Alcohol Syndrome (FAS) Phenytoin (Dilantin) Varicella Examples of Non-Teratogenic Agents: Spermicides, Acetaminophen, Prenatal Vitamins, Using a Microwave to Cook Food Identifying Teratogens Non-Traditional Inheritance Uniparental Disomy: Prader-Willi Syndrome, Angelman Syndrome Trinucleotide Repeats: Fragile-X Syndrome Mitochondrial Inheritance: Leber's Optic Atrophy Evaluating a Child for Birth Defects Overview of Newborn Screening for Birth Defects Medical History and Genetic Testing Testing for Birth Defects Chromosome Studies: Karyotype, Extended Banding, Fluorescence In Situ Hybridization (FISH), and Chromosomal Microarray Analysis Studies for Single Gene Defects: DNA (Direct and Indirect) Biochemical Genetic Testing Uses of Genetic Testing Genetic Services: When, Where, How Identification, Treatment, and Prevention of Birth Defects The Human Genome Project Vitamin, Gene, and Enzyme Replacement Therapy Before Your Next Pregnancy When to Seek Genetic Counseling Glossary Support Groups