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Genetics
| Question | Answer |
|---|---|
| Difference between Hereditary and Congenital | Hereditary disorders are passed from parents, transmitted through games (FAMILIAL). Congenital implies "present at birth" not always hereditary and not al genetic diseases are congenital. |
| Types of Genetic Disorders | 1) Mendelian Disorder (autosomal dominant, autosomal recessive, x-linked) 2) Multifactorial (Polygenic) inheritance 3) Cytogenic disorders (chromosomal abnormalities) autosomes & sex chromosomes |
| Mendelian Disorders (diseases caused by single-gene deffects) | defects caused by a SINGLE gene mutation may lead to numerous phenotypic alterations (Pleiotrophy) = multiple phenotypic expression |
| Genetic Heterogeneity | a phenomenon in which a single phenotype or genetic disorder may be caused by any one of a multiple number of Alleles or Non-allele (locus) mutations |
| Heterozygous | When one chromosome in the pair is affected |
| Homozygous | both chromosomes at a given gene locus (location) are affected |
| Codominance | some diseases where BOTH alleles of a gene pari is fully expressed |
| Autosomal Dominant | Approximately half of the offsprings will have the disease if only ONE parent is affected. Occasionally affected individual may not have affected parents because mutation arose from a new mutation. |
| What is Reduced or Incomplete Penetrance? | individuals with mutant genes that fail to express |
| What is Variable Expressivity? | Traits seen in all individuals carrying mutant gene by expressed differently among individuals |
| 4 main Autosomal Dominant Conditions | 1) Marfan Syndrome 2)Ehlers-Danlos Syndromes 3) Familial Hypercholesterolemia 4)Neurofibromatosis |
| Marfan Syndrome | Defective formation of FIBRILLIN, an integral part of elastic fibers. principle problems present in skeleton, eyes, and cardiovascular system. Prevalence is 1:5K with 70-85% familial and 30-15% new mutation. |
| Clinical Features of Marfan Syndrome | Elongated bones (legs, arms, fingers, deformed chest (pigeon chest) high arched palate, hyperextensibility of joints), Visual (lens may dislocate), Cardiovascular system (aneurysm, faulty valve, aortic rupture is common) |
| Ehlers-Danlos Syndrome (autosomal dominant, autosomal recessive, x-linked) | encompass a group of genetic varians, all of whihc share certain clinical features secondary to defective collagen formation. Exhibit a wide Variety of Inheritance Pattern |
| Clinical Features of Ehlers-Danlos Syndrom | Sking is hyperextensible but fragile and vulnerable to trauma, Joins are hypermobile typically seen in contortionists, Internal complications (colon rupture, large arterial rupture, corneal rupture and/or retinal detachment, diaphragmatic hernia) |
| Familial Hypercholesterolemia | most common of Mendelian disorder, hypercholesterolemia are typically NOT genetic. mutation in LDL receptor with excessive biosynthesis of and impared transport and catabolism of LDL = excessive plasma LDL. five-fold risk of death from MI by age 20. |
| Neoplasia consist of what two types of genes? | Proto-oncogenes & Growth suppressors - regulate normal cell growth and differentiation. |
| What are the two similar but different disorders associated with Neruofibromatosis? | Neurofibromatosis-1 & Neurofibromatosis-2 |
| Neurofibromatossis-1 | aka von Recklinghausen disease of Skin - arises from mutation of the Tumor Supressor Neurofibromin (Cafe-au-lait Pigmentation & Lisch Nodules) |
| Cafe-au-lait Pigmentation | pigmented birthmarks.The name café au lait is French for "coffee with milk" and refers to their light-brown color. |
| Lisch Nodules | a pigmented hamartomatous nodular aggregate of dendritic melanocytes affecting the iris |
| Neurofibromatosis-2 | arises from mutation of the Tumor Suppressor Merlin Gene on chromosome 22. defining feature is Bilateral Acoustic Neuromas (schwannomas or neurilemomas) of the vestibular nerve. affected pts at risk for multiple schwannomas and cafe-au-lait |
| Autosomal Recessive | traits expressed only if both alleles at a given locus are affected (homozygous), parents are carriers but do not express, offspring has a 1 in 4 of having it and a 1 in 2 chance of being a carrier. |
| 4 main Autosomal Recessive Disorders | 1) Cystic Fibrosis 2) Phenylketonuria 3) Galactosemia 4)Storage Diseases |
| Cystic Fibrosis | defective transport of chloride ions across epithelial cells resulting in low H2O secretion and Mucoviscidosis (viscous mucous), affects secretion of exocrine glands and lining of respiratory, GI, and reproductive tract. |
| what is the name of the mutation specific for Cystic Fibrosis? | Cystic Fibrosis Transmembrane Conductance Regulator gene (CFTR gene), it is isolated on chromosome 7. |
| Clinical Manifestations of Cystic Fibrosis | viscid mucus build-up in the pancreas, salivary gland, pulmonary complications, small bowel obstruction (Meconium Ileus), bile duct blockage (GI malabsorption, cirrhosis of the liver), reproductive tract blockage (infertility in men). |
| Diagnosis of Cystic Fibrosis | based on clinical presentation, sweat test (increased electrolytes, Na & Cl), and CFTR gene. |
| Phenylketonuria (PKU) | compound heterozygous mutations in the gene for the hepatic enzyme Phenylalanine Hydroxylase (PAH), rendering it nonfunctional. cant convert phenylalanine to tyrosine. |
| Clinical Manifestations of Phenylketonuria | mutation can cause Severe mental retardation (<4%), 30% never walk, 60% never talk, siezures, decreased pigmentation, musty odor. |
| Maternal PKU | high levels of phenylalanine can cross the placenta and produce mental retardation & multiple congenital defects in the fetus |
| Galactosemia | genetic metabolic disorder that affects an individual's ability to metabolize the sugar galactose, most serious enzyme loss is Galactose-1-Phosphate Uridyltransferase (affects liver, eyes, & CNS) |
| Clinical Presentation of PKU | affected infants vomit & develop diarrhea, jaundice & hepatomegaly (fatty change) in the first week w/o intervention, cataracts w/in first few weeks, and mental retardation in first yr of life. |
| Diagnosis/treatment of PKU | confirmed by identification of enzyme deficiency in blood cells, treat with galactose free diet for the first two yrs of life. |
| Storage Diseases | Except for von-Gierke & McArdle disease, every storage disease is secondary to defects in Lysosomes (Lysosomal Storage Disease) |
| 3 main Storage Diseases | 1) Sphingolipid storage disease 2)Mucopolysaccharide storage disease 3) Glycogen storage disorders |
| Sphingolipid storage diseases | 1) Tay-Sachs Diseases 2) Niemann-Pick 3) Gaucher Disease |
| Tay-Sachs Disease | lacks lysosomal Hexosaminidase A, a progressive deterioration of nerve cells and of mental and physical abilities, infants who are born suffer mental retardation, blindness, and cns dysfunction |
| Niemann-Pick Disease | lack of lysosomal Sphingomyelinase, accumulation of sphingomyeling and cholesterol affecting spleen, liver, bone marrow, lymph nodes, lungs and cns. |
| Gaucher Disease | exhibit deficiency in lysosomal Glucocerebrosidase, fatty substances (sphingolipids) accumulate in cells and certain organs. |
| Mucopolysaccharide Storage diseases | defective degradation of mucopolysaccharides, represented by Hurler Disease which lacks the alpha-L-iduronidase. coarse facial feature are termed Gargoylism due to skeletal deformities. |
| milder pattern of Mucopolysaccharidosis | Hunter Syndrome, exhibits lack of L-iduronate sulfatase. |
| Glycogen storage disorder | deficiency in enzyme involved in glycogen synthesis or degradation. Von-Gierke Disease, McArdle syndrome, and Pompe Disease. |
| Von-Gierke disease | hepatic type disease, lacks glucose-6-phosphatase in liver cells, accumulation of glucose in hepatocytes |
| McArdle Syndrome | myopathic type disease, lacks muscle phosphorylase = lack of glycolysis, associated muscle weakness presented as cramps. |
| Pompe Disease | Generalized Glycogenosis lacks Lysosomal Acid maltase, glycogen accumulates in almost all organs but predominantly in liver and cardiac and striated muscle. |
| X-Linked Disorders | disorders transmitted on the sex chromosomes rather than autosomes (aka Sex-linked) |
| What are the 2 types of X-linked disorders? | X-linked Recessive, and X-linked Dominant |
| X-linked Recessive | Heterozygous females are carriers, homozygous females and hemizygous males are affected. Common features: Lyonization and Unfavorable Lyonization |
| Lyonization | presents as either maternal or paternal X is inactivated in each cell and inactive X remain inactive in the progeny of the cell. |
| Unfavorable lyonization | inactivation of abnormally high percentage of normal X chromosome (example: Hemophilia A - lack factor VIII intrinsic clotting pathway) |
| what genotype is X-Linked Dominant? | Hererozygous, homozygous, and hemizagous are affected. (examples: Vitamin D resistant Rickets) |
| Multifactorial (polygenic or multigenic) disorders | additive effects of many genes of small effect that have been conditioned by the environment. disorders run in families due to sharing of effector genes & environment. |
| Karyotype (normal) | the number and appearance of chromosomes in the nucleus of a eukaryotic cell, each chromosome set can be seen alternating light and dark bands. (normal is 23 pairs of chromosomes: 22 autosomes & 1 sex chromosome) |
| What is an Euploid? | Normal chromosomal count (2x23 = 46) |
| Polyploidy | increased chromosome count that is multiple of what is normally seen (i.e. 3x23 or 4x23) and results in spontaneous abortion. |
| Aneuploidy | any number that is not an exact multiple of the normal chromosome count |
| Trisomy | example of extra chromosome 2x23+1 = 47 |
| Monosomy | example of absence of a chromosome 2x23-1 = 45 |
| Mosaicism | denotes the presence of two or more populations of cells with different genotypes in one individual who has developed from a single fertilized egg. |
| Translocation | transfer of a part of one chromosome to another nonhomologous chromosome. |
| Reciprocal Translocation | fragments that are exchanged between two chromosomes |
| Deletion | loss of a portion of a chromosome |
| Inversion | when chromosome breaks in two points, then the released fragment is reunited after a complete turnaround. |
| What are the two type of Chromosomal Aberrations? | Autosomal Aberrations and Sex Chromosomal Aberrations |
| Name one common Autosomal Aberration | Down Syndrome |
| Down syndrome | not hereditary, maternal age has a strong influence, most common of Chromosomal Disorders |
| Clinical significance of Down syndrome | Trisomy of chromosome 21(47 chromosomes), 1/1550 when mom is under 20, and 1/25 when mom is over 45 yrs of age. |
| Clinical Presentation of Down sundrome | epicanthal folds, flat face, low IQ, susceptible to infections, perio problems, increased risk of leukemia, cardiac malfunctions (>40% of deaths), patients older than 40 develop neuropathic changes of Alzheimer. |
| Sex Chromosome Abberations | not rare, due to lionization and the sparse Y chromosome. two main types Klinefelter Syndrome and Turner Syndrome |
| Clinical significance of Kleinefelter Syndrome (Testicular Dysgenesis) | genotypical males with extra X chromosomes, 1/5000 like male births, 15% have Mosaicism (47 XXY and 48 XXXY) |
| Clinical presentation of Kleinefelter Syndrome (Testicular Dysgenesis) | testies atrophies, STERILITY (principle effect), long legs, reduced hair, Gynecomastia (male breast, increased risk of cancer), lower intelligence (worse w/ more X chromosomes) |
| Turner Syndrome | 45-XO karyotype, only recognized monosomy compatible with life, 57% missing second X chromosome in all cells, 43% are mosaic or partial deletion (almost normal appearance & present only with Primary Amenorrhea) |
| Primary Amenorrhea | congenital absence of the uterus, failure of the ovary to receive or maintain egg cells (menstruation cycles never starting) |
| Clinical presentation of Turner syndrome | little pubic hair, inadequate breast, short stature, webbing of neck, digits, lower set ears, coarctation (narrowing) of the aorta |
| 4 main methods for diagnosing genetic diseases | karyotyping, abnormal gene products, fluorescence in situ hybridization (FISH), molecular analysis |
| Barr Body | mass of sex chromatin w/in the nucleus of cells, originates form inactivation of X-chromosome in those with two X chromosomes |
| Hemizygous | possessing only one of a pair of genes that influence the determination of a particular trait |
| Monosomy | the absence of one chromosome |
| Trisomy | presence of extra autosome or sex chromosome |
| Pediatric Diseases | Highest risk of mortality in the first year. Respiratory Distress Syndrome, Sudden Infant Death Syndrome (SIDS), Erythroblastosis Fetalis, ABO incompatibility |
| Respiratory Distress syndrome | disease of premature infant due to lack of Surfactant, affects 60% born before 28 wks--60K cases, 5K mortalities, can result in long term neuro defects, Chronic lung disease |
| Clinical Presentation of Respiratory Distress Syndrome | normal leading to hypoxia, formation of Hyaline Membrane Lining alveoli (mat of fibrin mixed with necrotic cells). Treat with corticosteroids, ventilation, aerosolized surfactant but best to delay birth for as long as possible. |
| Sudden Infant Death Syndrome (SIDS) | sudden, unexpected, unexplained deaths prior to 1 yr old. 3000 annually, 90% under 6 months, most 2-4 months |
| Clinical significance of SIDS | death usually occur during sleep and with increased prevalence in infant who sleep in a prone position. lay baby on their back "Back to sleep" which has reduced SIDS by 40% |
| Erythroblastosis Fetalis (hemolytic disease of newborn) | arises when mother is Rh(-) and fetus is Rh(+). mother forms antibodies against Rh(+) surface antigens. typically first baby is spared from antibody attack but second baby is in trouble. |
| Clinical significance of Erythroblastosis Fetalis | can develop severe hemolytic disease due to hemolysis and anemia. surviving baby can develop Hypervilirubinemia which is a build up of Bilirubin that can cross blood-brain barrier and cause cns damage (KERNICTERUS) |
| ABO incompatibility | similar problem arising in infants with type A or B blood who come from type O mothers. disease is much less severe than with Erythroblast Fetalis. 20-25% of pregnancies and only a small fraction of newborns develop hemolytic disease. |
| Types of Tumors of Infancy and Childhood | Benign Neoplasms and Malignant Tumors |
| Benign Neoplasms | Hemangiomas and Lymphangiomas |
| Hemangioma | most common tumors of infancy & consist of overgrowth of vascular channels. |
| Characteristics of Hemangiomas | Cavernous Hemangioma, Capillary Hemangioma, Port Wine Stain/Vascular Nevus. tumors may grown along with child by typically regress with age. |
| Cavernous Hemangioma | large vessels |
| Capillary Hemangioma | small diameter vessels |
| Port wine stain/Vascular Nevus | occur on children skin and vary from flat areas of increased vascularity to large irregular nodules |
| Lymphangiomas | consist of cystic and cavernous spaces lined by endothelium and filled with pale fluid (serum w/out cellular element). lymphoid aggregates in surrounding stroma. many remain stable and require no therapy. |
| 3 common types of Malignant Tumors | Neuroblastoma, Retinoblastoma, Wilms Tumor (nephroblastoma) |
| Neuroblastoma | most common extracranial tumor of childhood, 7-10% of pediatric neoplasms, originates from neural crest cells. maturation of neuroblastoma is characterized by Ganglioneuroblastoma and Ganglioneuroma. |
| Ganglioneuroblastoma | neuroblastoma surrounded by Ganglion cells |
| Ganglioneuroma | increased ganglion cells intermixed with cell proliferation of Schwann cells. |
| Retinoblastoma | rapidly developing cancer of the retina (intraocular malignancy), 40% inherited mutation of the RB gene and the rest are sporadic, avg age occur at 2yrs old, familial retinoblastoma are at increased risk for developing osteosarcoma (soft tissue tumors) |
| Wilms tumor (nephroblastoma) | cancer of the kidney typically in children between 2 - 5 yrs of age. associated with congenital malformation and chromosomal alteration. loss of cancer suppressor gene leading to future neoplasia. |
| Clinical presentation of Nephroblastoma | present with large tumor that creates a significant abdominal mass. |
Created by:
ddde227
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