Diseases Flashcards

1
Q

Wilson’s Disease

A

Autosomal recessive condition caused by mutation in ATP7B gene; ATP7B protein transfers excess copper into the blood stream

Results in liver cirrhosis & neurological deficiency

Suspected by Kayser-Fleischer rings

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2
Q

Kayser-Fleischer rings

A

Corneal deposits of copper visible on eye exam

+ sign of Wilson’s Disease

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3
Q

Trisomies Compatible with Life

A
Trisomy 13 (Patau Syndrome) 
Trisomy 18 (Edward's Syndrome) 
Trisomy 21 (Down's Syndrome)
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4
Q

Patau Syndrome

A

Trisomy 13; characterized by severe intellectual disabilities, failure of the embryonic forebrain to divide properly (holoprosencephaly), facial clefts, polydactyly, renal anomalies, congenital heart and urogenital defects

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5
Q

Edward’s Syndrome

A

Trisomy 18; characterized by dysmorphic facial features (receding jaw, low-set ears), intrauterine growth retardation, clenched fists, valvular heart disease, diaphragmatic hernia, renal anomalies

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6
Q

Hirschprung disease

A

Often seen in Trisomy 21; results from lack of embryonic migration of nervous tissue to the colon, leading to inability of the colon to relax and pass stool, creating obstruction; entire colon, stomach, and esophagus may be affected in rare cases

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7
Q

Klinefelter Syndrome

A

47 XXY as a result of errors in either maternal meiosis (I or II) or paternal Meiosis I; characterized by tall stature, hypogonadism, gynecomastia, sterility, and learning disabilities

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8
Q

Turner Syndrome

A

XO, most often resulting from loss of the paternal X chromosome; characterized by short stature, webbed neck, broad chest, ammenorrhea, renal & cardiovascular anomalies (bicuspid aortic valve, aortic coarctation)

15% mosaicism

*Loss of function mutation

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9
Q

Hemophilia A

A

X-linked disorder of coagulation caused by mutation in the F8 gene which codes for Factor VIII, an enzymatic cofactor involved in clotting combination; characterized by spontaneous bleeding into joints, muscles, or intracranial & excessive bruising

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10
Q

Hemophilia B

A

X-linked disorder of coagulation caused by mutation in the F9 gene which codes for Factor IX, a protease involved in clotting

No common F9 mutation is known; Hemophilia B Leyden results from point mutations in the F9 promoter and resolves at puberty

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11
Q

Chromosomal abnormalities underlying Down Syndrome

A

Trisomy 21, usually as a result of nondisjunction in maternal meiosis (95%)

Robertsonian translocation between 21q and the long arm of one of the other acrocentric chromosomes; 46 chromosomes, effectively trisomic for genes on 21q (4%, risk unrelated to maternal age)

Isochromosome 21 - results from a 21q21q translocation in which 21p is deleted and 21q is duplicated in a mirror-like fashion; all gametes are either monosomic (lethal) or trisomic (Down)

Mosaic Down Syndrome - cell populations have both normal and Trisomy 21 karyotype (1-2%)

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12
Q

Neurofibromatosis (NF1)

A

Autosomal dominant condition resulting from loss of function mutation in NF1 gene, which codes for neurofibromin tumor suppressor

Example of pleiotropy: Characterized by growth of benign fleshy tumors (neurofibromas), cafe au lait spots, small benign tumors on the iris (Lisch nodules), & freckling of the axillary/inguinal region

*Loss of function mutational mechanism

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13
Q

Cri du Chat Syndrome

A

Results from deletion of part of 5p15; characterized by microcephaly, epicanthal folds, low-set ears with preauricular tags, moderate to severe intellectual disability, and heart defects

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14
Q

XYY Syndrome

A

Results from paternal nondisjunction at meiosis II, producing YY sperm; generally indistinguishable from XY males except for mild learning disability

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15
Q

Trisomy X

A

XXX resulting from errors in maternal meiosis I, two of the X chromosomes are inactivated; phenotypically normal, may exhibit some intellectual/learning disability and behavioral problems

Tetrasomy X and Pentasomy X are possible and associated with increasingly impaired physical and mental development

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16
Q

Charcot-Marie-Tooth (CMT-1A)

A

Autosomal dominant disorder caused by a duplication of the PMP22 gene on chromosome 17; characterized by muscle atrophy of the foot, lower leg, and hand muscles, and hammertoes, due to peripheral nerve demyelating neuropathy

*Gain of function mutation

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17
Q

Hereditary Neuropathy with Predisposition to Pressure Palsy (HNPP)

A

Autosomal dominant condition resulting from deletion of PMP22 gene on Chromosome 17, coding for PMP22 protein which is an integral membrane glycoprotein in nerves; presents as focal pressure neuropathy in 20s-30s

*Loss of function mutation

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18
Q

An example of contiguous gene syndromes

A

Velocardiofacial Syndrome and DiGeorge syndrome, both caused by del 22q11, a common cause of cardiac defect

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19
Q

Prader-Willi Syndrome

A

Caused by deletion of 15q11-13 on the paternal homolog (or uniparental disomy of the maternal chromosome); characterized by almond-shaped eyes, excessive & indiscriminate eating, obesity, short stature, strabismus & nystagmus, hypotonicity, mild-moderate cognitive disability

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20
Q

Angelman Syndrome

A

Caused by deletion of 15q11-13 on the maternal homolog; characterized by short stature, spasticity, seizures, autism, and intellectual disability

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21
Q

Acute Promyelocytic leukemia (PML)

A

Characterized by translocation involving the retinoic acid receptor-alpha (RARA) gene on 17 and the promyelocytic leukemia (PML) gene on 15; the translocation produces a PML-RARa fusion protein that binds to the RAR element in the promoters of certain genes necessary for proper myeloid differentiation, blocking transcription

Treatment with retinoic acid (vitamin A) (differentiation therapy)

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22
Q

Chronic Myeloid Leukemia (CML)

A

Characterized by translocation between the breakpoint cluster region (BCR) gene on 22 with the ABL gene 9 - the “Philadelphia chromosome; this translocation produces the BCR-ABL fusion protein, a constituively active tyrosine kinase, leading to myeloproliferative disease

Treatment: Gleevec (a tyrosine kinase inhibitor)

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23
Q

DiGeorge Syndrome

A

Caused by a deletion on 22q; characterized by developmental delay, ADHD, and aortic defects

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24
Q

Down Syndrome phenotypic features

A
Flattened facial features
Upslanting palpebral fissures
Epicanthal folds
Small ears
Low muscle tone/increased joint mobility
Transverse Palmar Crease
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25
Medical Issues associated with Down Syndrome
Cardiac anomalies (30-50%), especially atrioventricular septum defects Esophageal/duodenal atresia Hirschprung Disease GERD Nystagmus Cataracts Chronic ear infections & nasal congestion Obstructive apnea Thyroid disease, most commonly hypothyroidism Increased risk of leukemia (12-20x) Early onset Alzheimer's
26
IDIC 15
Characterized by presence of an extra, inverted duplicated isodicentric chromosome 15q, in addition to the 2 normal copies, resulting in partial trisomy of this region; characterized by Autism & seizures, NOT dysmorphic
27
Maternally inherited interstition duplication of 15q
Interstitial duplication of a region of 15q leads to partial trisomy for these genes; presentation is similar to IDIC 15 including autism and seizures, NOT dysmorphic Paternal duplication of 15q show normal phenotype
28
Fragile X Syndrome
Caused by an expansion in the number (>200) of CGG repeats in the 5' UTR of the FMR1 gene, causing excessive methylation of the promoter and failure to express the FMR1 protein; characterized by intellectual disability, dysmorphic features, autistic behavior Demonstrates genetic anticipation through the maternal germ line
29
Acute Lymphoblastic Leukemia (ALL)
Caused by translocation between the TCF3 gene on chromosome 1 and the PBX1 gene on chromosome 19 Hyperdiploidy (>51 chromosomes) is associated with a good prognosis Children with TPMT enzyme deficiency must be given 10% standard dose
30
Recurrence Risk for Down Syndrome caused by maternal nondisjunction
1/100 + age-related risk
31
Maturity onset diabetes of the young (MODY)
Beta cell destruction (characteristic of Type I) with later-onset presentation (characteristic of Type II) Example of variable expressivity: Many individuals with mutations in the same codon exhibit widely varying age of diagnosis
32
Cystic Fibrosis
Autosomal recessive disease caused by mutation in the CFTR gene, which codes for a sodium/chloride channel, causing build up of thick mucus secretions Ex: of allelic heterogeneity: Mild/mild or mild/severe alleles lead to 15% pancreatic insufficiency whereas severe/severe alleles leads to 85% pancreatic insufficiency
33
PKU
Autosomal recessive condition resulting from defect in the PAH gene on 12q encoding phenylalanine hydroxylase, a liver enzyme that catalyzes the breakdown of Phe; a small fraction (1-3%) have normal PAH but are defective in genes needed for the synthesis of BH4, the cofactor of PAH Most PKU patients are compound heterozygotes
34
PKU Phenotype
Microcephaly, seizure, tremor, gait disorders, and mental retardation; high [Phe] and low [Tyr] in plasma due to defective conversion pathway
35
Maternal PKU
Pregnant women with PKU have increased risk of miscarriage/congenital malformation, mental retardation, and growth impairment due to elevated Phe levels in maternal circulation during fetal development; these women should be maintained on a low-Phe diet
36
Detection of PKU
Bacterial growth in Guthrie test is diagnostic for PKU Mass spec in newborns to determine levels of Phe in blood specimen; babies should be tested after birth and again several days later in order to avoid false-negatives caused by normal PAH in maternal blood supply Affected babies are treated early with low-Phe diet; BH4-deficient PKU patients are treated with oral BH4 and low-Phe diet
37
alpha 1-antitrypsin deficiency (ATD)
Autosomal recessive disease caused by mutation in the SERPINA1 gene on chromosome 14, which codes for a serine protease inhibitor that targets elastase; left uninhibited, elastase can destroy the connective tissue proteins of the lung, causing emphysema *May be treated with recombinant AT1 protein replacement therapy
38
ATD Phenotypes
Increased risk of emphysema (more severe among smokers) and liver cirrhosis/carcinoma, due to accumulation of misfolded, secreted SERPINA1 mutant protein accumulation in the liver ER (Z allele)
39
ATD genotypes
M allele is wild type; most ATD diseases are associated with Z and S mutant alleles: Z allele encodes a misfolded protein that aggregates in the liver, causing lung AND liver damage; Z/Z genotypes have only 10-15% normal SERPINA1 activity and develop disease S allele encodes less effective protein; S/S genotype have 50-60% normal SERPINA1 activity and do not express disease symptoms Z/S compound heterozygotes have 30-35% normal SERPINA1 activity and may develop mild disease
40
Tay Sach's Disease (T-S)
Autosomal recessive disorder caused by HEXA gene mutation, which codes for the alpha subunit of hexosaminidase A (HexA), a heterodimer of alpha and beta subunits; HexA is needed to metabolize GM2 ganglioside; GM2 accumulates in the lysosomes of CNS neurons causing neurodegeneration HexA defective, HexB normal Cherry Red spot in the eye is common clinical sign
41
Tay Sach's Phenotype
Onset of symptoms occurs around 3-6 months with muscle weakness, seizures, vision/hearing loss, diminishing mental function, paralysis, and death by 3-4 years. 100x higher risk in Ashkenazic Jewish population; also French-Canadian communities of Quebec, Pennsylvania Amish, and Louisiana Cajun
42
Sandhoff Disease
Caused by a defect in the HEXB gene which codes for the beta subunit of both HexA (aB) and HexB (BB) enzymes; same neurological symptoms as T-S Both HexA and HexB defective
43
A-B Variant of Tay-Sachs
Rare form of T-S in which both HexA and HexB are normal but GM2 accumulates due to a defect in the GM2 activator protein (GM2-AP), which facilitates interaction between the lipid substrate GM2 and the HexA enzyme HexA and HexB both functional but HexA shows diminished functionality
44
Tay-Sachs Screening
DNA tests or enzymatic activity assay can distinguish carriers, who have lower HexA enzyme levels in the blood; enzyme test can also be performed on amniotic fluid cells to detect TS fetus in utero
45
Sickle Cell Anemia (HbSS)
Autosomal recessive condition caused by a single base mutation in the B-globin gene resulting in a Glu --> Val missense mutation; HbS is 80% less soluble than HbA and polymerizes into long fibers that distort the RBC into a sickle shape that becomes lodged in the micro-capillaries Heterozygotes are phenotypically normal except under conditions of low pO2 * Novel Property Mutation * Butyrate treatment increases production of HbF and reduces polymerization of HbS
46
Hemoglobin C Disease (HbCC)
Autosomal recessive condition caused by a single base mutation in the B globin gene, resulting in a Glu --> Lys missense; HbC is less soluble than HbA and tends to form crystals, reducing the deformability of RBC and shortening the cell's lifespan Heterozygotes are phenotypically normal except under conditions of low pO2 *Same codon is mutated as in HbS
47
HbS Diagnosis
Restriction enzyme MstII recognizes a certain recognition site in HbA that is destroyed by the Glu --> Val mutation in HbS; digestion with this enzyme of HbS mutant DNA yields a 1.35 kb fragment instead of two (1.15 and .20 kb) fragments MstII can distinguish HbA and HbS but not HbA and HbC since the HbC mutation does not affect the MsII recognition sequence HbA, HbS, and HbC can also be diagnosed by hemoglobin electrophoresis, in which differently charged variants migrate toward (+) at varying speeds due to their mutated codons
48
a-Thalassemias
Anemic disorders caused by deletion of one or both copies of the a-globin gene on the a-cluster of chromosome 16 *Loss of function mutation
49
a-thal-1 allele
Caused by deletion of both copies of a-globin genes in the a-cluster; homozygous state (--/--) results in stillborn whereas heterozygous (aa/--) have mild anemia a.k.a. a-thalassemia-1 trait (50% globin production) Common in Southeast Asia
50
a-thal-2 allele
Caused by deletion of one of the two a-globin genes in the a-cluster; heterozygotes (aa/a-) are silent carriers whereas homozygotes (a-/a-) express a-thalassemia trait (50% globin production) Common in Africa, Meditteranean, and Asia
51
a-thal-1/a-thal-2 (HbH Disease)
Caused by compound heterozygosity for a-thal-1 & a-thal-2 alleles (a-/--); individuals produce only 25% normal a-globin levels resulting in severe anemia; marrow compensates by producing higher levels of HbH form (B4), which precipitates and may lead to hydrops fetalis (generalized edema)
52
Clinical categorization of B-Thalassemias
Thalassemia major (Cooley's Anemia): Severe anemia due to inherited deletion of both maternal & paternal B-globin genes; presents with osteopenia, hepatosplenomegaly; patients are treated with transfusion & iron chelation Thalassemia Intermedia: Mild-moderate anemia caused by inheritance of 2 mildly/moderately abnormal B globin genes; patients are sometimes transfusion dependent Thalassemia minor: Clinically insignificant condition caused by inheritance of 1 abnormal B-globin gene (B-thal trait); may display < MCV (small RBCs)
53
Molecular categorization of B-thalassemia
Simple B-thalassemia: Caused by genetic mutations or deletions in the B cluster on 11p that impair the production of the B-globin chain alone; other genes in B-cluster unaffected Complex B-thalassemia: Caused by large deletions in the B cluster on 11p that remove the B-globin gene PLUS other genes in the B-cluster, or the LCR
54
Biochemical Classification of B-thalassemia
B+ thalassemia: Some B-globin is made and some HbA is present; decreased B-globin synthesis caused by mutations affecting transcription, RNA processing, or protein stability B- thalassemia: No B-globin synthesis and no HbA present; caused by deletion of the B-globin gene or nonsense/frameshift mutation leading to premature stop codon; Hb present at <5% normal levels (a2y2 and a2d2 variants), which is lethal
55
Hereditary Persistent Fetal Hemoglobin (HPFH)
Caused by deletions in the promoter region of the B globin gene OR by large deletions in the B-cluster including d- and B-globin genes; 100% of Hb is HbF (a2y2) Disease-free phenotype *Heterochronic mutation mechanism
56
Duchenne Muscular Dystrophy
X-linked recessive disorder caused by mutation of DMD gene on Xp coding for dystrophin protein; boys present with calf hypertrophy, abnormal gait at 3-5 years with progressive involvement of respiratory muscles; median age of death = 18 years *Loss of function mechanism In-frame deletions of Xp21 lead to partially functional protein, milder Becker muscular dystrophy
57
Osteogenesis Imperfecta Type I
Autosomal dominant condition caused by premature termination mutation in COL1A1 gene, which codes for COL1A1 protein necessary for production of collagen triple helix; patients make normal collagen helices in reduced amounts Present with brittle bones, increased fractures, blue sclerae, normal stature *Loss of function mechanism
58
Hemoglobin Kempsey
Missense mutation in the beta-hemoglobin gene preventing T/R switching; Hb remains "locked" in the R state (which has higher O2 affinity) and cannot unload O2 in the tissues, leading to production of more RBCs (polycythemia) *Gain of function mutation
59
Osteogenesis Imperfecta Types II, III, IV
Caused by mutation in COL1A2 gene leading to production of protein with an abnormal (novel) structure; half of collagen triple helices will incorporate this abnormal protein and produce an abnormal collagen trimer, leading to severe phenotype, often fatal *Novel property mechanism
60
Huntington Disease
Autosomal dominant disorder characterized by > 40 (CAG)n repeats (coding) and expanded polyglutamine tracts in the HTT gene on 4p coding for Huntingtin protein; number of repeats corresponds with absence/presence of disease phenotype as well as age-of-onset Genetic anticipation occurs through the paternal line
61
Myotonic Dystrophy (MD)
Autosomal dominant condition caused by expanded CTG repeats in the 3' region of the DMPK gene, leading to production of abnormal RNA (no mutant protein produced); expansion of these repeat sequences is carried through the maternal line; characterized by facial weakness, ptosis (eyelid drooping), and myotonia (delayed muscle relaxation after voluntary contraction)
62
Genetic Disorders of Hemoglobin - 3 types
Structural variants - normal synthesis of Hb but altered globin property (ex. solubility, stability) Thalassemia - decreased or absent production of one globin chain Defective Globin Switching - Hereditary persistence of fetal Hb
63
Hb Kansas
Hb remains locked in low O2 affinity "T" state; leads to low O2 levels in the tissues presenting as cyanosis
64
Achondroplasia
Autosomal dominant disorder caused by gain-of-function mutation in fibroblast growth receptor 3 (FGFR3), a transmembrane tyrosine kinase receptor; constitutive activation of the protein inhibits chondrocyte proliferation within the growth plate leading to shortening of the long bones Characterized by rhizomelic shortening of the limbs, midface hypoplasia; 10% risk of brainstem compression, 3-7% die unexpectedly in first year of life Homozygotes are more severely affected (incomplete dominance); spontaneous mutations occur in the father's germline and increase in frequency with advanced paternal age > 35 years *Gain of function mutational mechanism
65
Marfan Syndrome
Autosomal dominant condition caused by mutation in the fibrillin 1 gene (FBN1) on 15q, an extracellular matrix protein component of connective tissue; characterized by tall stature, mitral valve prolapse, aortic dilation/rupture
66
Polycystic Kidney Disease (PKD)
Autosomal dominant condition caused by mutation in PDK1 or PDK2 encoding polycystin 1 & 2 protein; characterized by renal & hepatic cysts & progressive renal failure Ex. of locus heterogeneity
67
Familial Hypercholesterolemia
Autosomal dominant condition resulting from mutation in the LDLR gene encoding the LDL receptor, which normally functions to bind LDL and deliver it to the cell interior; in the disease form, LDL deposits in the coronary arteries (atheromas), in the skin and tendons (xanthomas), and in the cornea (arcus cornea)
68
DMD-associated dilated cardiomyopathy
Weakening & enlargement of the heart as a result of a lack of dystrophin in the myocardium; usually presents between 20-40 years of age without skeletal muscle involvement
69
Hydrops Fetalis
Massive, generalized edema resulting from 3 (--/a-) or 4 (--/--) gene alpha-globin deletion and subsequent compensation with HbH form (B4); hydrops fetalis resulting from 4-gene deletion is incompatible with life
70
Nonsyndromic Deafness
Congenital deafness (in the recessive form) or progressive childhood deafness (in the dominant form), caused by mutation in the GJB2 gene which codes for connexin26, a protein that forms gap junctions in the cochlea and enables the transduction of sound waves to electrical impulses Ex: of genetic heterogeneity, only 50% caused by GJB2 gene
71
Fabry Disease
X-linked disorder; caused by loss-of-function mutation in the alpha-galactosidase A enzyme activity leading to lipid accumulation; presents with microvascular disease, neuropathy, nephropathy, cardiomyopathy Can be treated with recombinant Alpha-Gal therapy
72
Pompe Disease
Autosomal recessive, caused by loss-of-function mutation in acid alpha-glucosidase enzyme causing accumulation of glycogen in the lysosome; characterized by severe, progressive muscular failure; infant-onset or late-onset Treated with recombinant alpha-glucosidase protein
72
Ushar Syndrome
Deafness + retinitis pigmentosa Autosomal recessive
73
Pendred Syndrome
Deafness + thyroid goiter Autosomal recessive
74
Jervell and Lange-Nielson Syndrome
Deafness + arrhythmia or sudden death Autosomal recessive
75
Waardenburg Syndrome
Deafness + white forelock Autosomal dominant
76
Neurofibromatosis Type II
Deafness + 8th nerve schwannomas
77
Fragile X-associated Tremor/Ataxia Syndrome (FXTAS)
X-linked premutation triplet repeat expansion (59-200 CGG) in FMR1 gene; characterized by adult onset ataxia, tremor, memory loss, peripheral neuropathy; in women, may also present with premature ovarian failure No hypermethylation, increased quantities of FMRP mRNA produced Genetic anticipation through the maternal line and expansion risk influenced by haplotype (AGGs reduce risk)