FINAL: MOLECULAR DETECTION OF INHERITED DISEASE Flashcards
Caused by mutations (changes) in germ cells that are passed down from parent to child
Inherited Diseases
Mutations in Somatic Cell:
- Cancer
- Congenital malformations
(present at birth)
- due to factors upsetting the developmental process
abnormal chromosome #
GENOME MUTATION
more than 2
POLYPLOIDY
gain (trisomy) or loss
(monosomy)
ANEUPLOIDY
Genome mutations Detection?
karyotyping, ploidy
analysis, flow cytometry, & FISH
- 2 or more genetically distinct populations of cells from 1 zygote in an individual
- Results from mutation events affecting somatic/germ cells
Mosaicism
- Trisomy 21, 47,XY, + 21
- 1/700 live births
- Flat facial profile, mental retardation, cardiac problems, risk of acute leukemia, eventual neuropathological disorders, abnormal immune system
Down syndrome
- Trisomy 18, 47,XY, + 18
- 1/3,000 live births
- Severe, clenched fi st; survival less than 1 year
Edward syndrome
- Trisomy 13, 47,XY, + 13
- 1/5,000 live births
- Cleft palate, heart damage, mental retardation, survival
usually less than 6 mo
Patau syndrome
- 47,XXY
- 1/850 live births
- Male hypogonadism, long legs, gynecomastia (male breast enlargement), low testosterone level
Klinefelter syndrome
- 47,XYY
- 1/1,000 live births
- Excessive height, acne, 1%–2% behavioral disorders
XYY syndrome
- 45,X and variants
- 1/2,000 live births
- Bilateral neck webbing, heart disease, failure to develop
secondary sex characteristics, hypothyroidism
Turner syndrome
- 47,XXX; 48,XXXX
- 1/1,200 newborn
females - Mental retardation increases with increasing X
Multi X females
- abnormalities in structure
- Translocations, inversions, deletions,
duplications, marker chromosomes,
derivative chromosomes
Chromosomal mutations
caused by
chemicals, radiation, chromosome
breakage syndromes (Fanconi
anemia, Bloom syndrome, ataxia
telangiectasia)
Chromosome breakage
is a genetically heterogeneous recessive disorder characterized by defective DNA repair
Fanconi anemia
- rare genetic disorder characterized by growth retardation, sun sensitive skin lesions, and an increased risk of cancer
BLOOM SYNDROME
- rare genetic disorder characterized by progressive neurological dysfunction, immune deficiencies and increase risk of cancer (like lymphoma and leukemia)
ataxia
telangiectasia
DETECTION OF CHROMOSOMAL ABNORMALITIES
karyotyping, FISH,
microarray technology (CGH)
Examples of Chromosomal Mutations
- del(22q)
- 1/4,000 live births
- CATCH 22 (cardiac abnormality/abnormal facies, T-cell deficit, cleft palate, hypercalcemia)
DiGeorge syndrome and
velocardiofacial syndrome
- del(5p)
- 1/20,000–1/50,000
live births - Growth deficiency, catlike cry in infancy, small head, mental retardation
Cri du chat syndrome
- del(11p
- 1/15,000 live births
- Aniridia (absence of iris), hemihypertrophy (one side of the body seems to grow faster than the other), and other congenital anomalies
Contiguous gene syndrome; Wilms’
tumor, aniridia, genitourinary
anomalies, mental retardation
syndrome
affect structural proteins, cell surface receptor proteins, growth regulators, and enzymes
Single-gene diseases
DOMINANCE RELATIONSHIPS
- Heterozygous phenotype (child = Tt)
- Homozygous phenotype (1 parent =
TT) Example: height
Complete dominance
DOMINANCE RELATIONSHIPS
- Offspring phenotype is variably intermediate (combine) between the
homozygous & heterozygous
parentals
- Example: gene affecting hair texture
Partial/incomplete dominance
DOMINANCE RELATIONSHIPS
- Simultaneously demonstrate the
phenotype of both parents
- Example: ABO blood group
Codominance
- A.K.A. transmission patterns/mode of inheritance
- The manner in which a genetic trait,
disorder, or risk of disorder is passed
from one generation to the next - Determined by examination of family histories
PATTERNS OF INHERITANCE IN
SINGLE GENE DISEASES
diagram of family
phenotype/genotype
Pedigree:
3 main patterns:
- autosomal dominant
- autosomal recessive
- sex-linked (X-linked)
- Criteria:
a. Males and females can be affected. Male-to-male transmission may occur.
b. Males and females transmit the trait with equal frequency.
c. Successive generations are
affected.
d. Transmission stops after a generation in which no one inherits
the mutation. - Affected individual = has dominant
allele - Parent 1 (affected) x Parent 2
(unaffected) = 50%-100% risk/likelihood of expressing the disease phenotype on the child
Autosomal Dominant Transmission
- Criteria:
a. Males and females can be
affected.
b. Affected males and females can
transmit the gene, unless it
causes death before reproductive
age
c. The trait can skip generations.
d. Parents of an affected individual
are heterozygous or have the
traits - Affected individuals =homozygous
recessive genotypes - Carriers heterozygotes/asymptomatic
Autosomal Recessive Transmission
- Common
- Always expressed in males
o inherit the trait from heterozygote/homozygote mother - Females are carriers and can only be expressed if the causative allele is
present in 2 copies
o inherit the trait from affected father and affected heterozygote mother - Ichthyosis, color blindness, hemophilia
X-linked recessive transmission:
- Rare
- Always expressed in females
o Passed from male to all daughters
M but to no sons - Expressed also in males, with more
severe effects - Rickets, Rett syndrome, incontinentia pigmenti, congenital hypertrichosis
X-linked dominant transmission
X-linked recessive diseases are carried
by females but manifested most often in _______.
MALES
- Freq. of expression of disease phenotype in individuals with a gene lesion
Penetrance
homozygous recessive
INCOMPLETE OR COMPLETE PENETRANCE?
COMPLETE PENETRANCE
- Range of phenotypes in individuals with the same gene lesion
Variable Expressivity
Molecular Basis of Single-Gene Diseases:
- Molecular methods,
morphological studies, clinical chemistry
Detection
Molecular Basis of Single-Gene Diseases:
- physiological, morphological and laboratory results
Final Diagnosis
- Cause: incompletely digested
macromolecules due to loss of enzymatic degradation (acid hydrolases) - Defects in proteins required for normal
lysosomal function
→ physical abnormalities - Molecular testing: genes that code for the enzymes & their subunits
LYSOSOMAL STORAGE DISEASE
LYSOSOMAL STORAGE DISEASE
SCREENING?
GENE PRODUCT TESTING
LYSOSOMAL STORAGE DISEASE
DETECTION OF MUTATION?
DIRECT SEQUENCING
Substrate Accumulated:
Sphingolipids
DISEASE?
Tay–Sachs disease
DISEASE:
Von Gierke, McArdle, and Pompe disease
SUBSTRATE ACCUMULATED?
Glycogen
DISEASE:
Hurler, Sheie (MPS I), Hunter (MPS II), Sanfi lippo (MPS III), Morquio (MPS IV), Maroteaux–
Lamy (MPS VI), Sly (MPS VII)
SUBSTRATE ACCUMULATED?
Mucopolysaccharides
DISEASE:
Pseudo-Hurler polydystrophy
SUBSTRATE ACCUMULATED?
Mucolipids
DISEASE:
Niemann–Pick disease
SUBSTRATE ACCUMULATED?
Sulfatides
Substrate Accumulated:
Glucocerebrosides
DISEASE?
Gaucher disease
Cause: Single point mutation in the coagulation factor V gene F5 (1q23) at exon 10 (GA at nucleotide 1691,R506Q)
- Genotype: heterozygous form (4%-
8% of the general population) & homozygous (0.06%-0.25%)
- Molecular methods: PCR-RFLP, SSP-PCR
- Other methods: Invader technology,
clot- based methods, family history
FACTOR V LEIDEN
FACTOR V LEIDEN
inherited blood
clotting disorder
Thrombophilia
Treatment for blood clot/deep venous
thrombosis?
anticoagulants
- Precursor to thrombin in the coagulation cascade
- Autosomal-dominant increased risk of thrombosis: mutation in the 3’ untranslated region of the gene that codes for prothrombin or coagulation factor II, F2 (11p11 -q12)x
- Laboratory tests: F2 & F5 mutations
- Molecular methods: multiplex PCR - RFLP
- Phenotypic methods: thrombin time, prothrombin time, platelet count, CBC
Other: sequencing of factors XI & XIII
PROTHROMBIN
measure changes in light transmittance during clot formation generating a curve
Automated systems
METHYLENETETRAHYDROFOLATE REDUCTASE
- autosomal recessive disorder caused by deficiency of the 5,10-
methylenetetrahydrofolate reductase (MTHFR) gene product
o Increased homocysteine levels → predisposition to venous & arterial thrombosis
Hyperhomocysteinemia
- Autosomal recessive condition, over absorption of iron from food → pancreas, liver, & skin damage; heart disease; diabetes
- Diagnosis: measurement of blood iron levels, transferrin saturation, liver biopsy
- Molecular cause: dysfunction of the hemochromatosis type I HFE or HLA-
H gene product (C282Y, H63D, S65C) - Indications for mutation testing:
clinical symptoms & increased serum
ferritin & transferrin-iron saturation - C282Y mutation detection: PCR-RFLP
HEMOCHROMATOSIS
- Life-threatening autosomal recessive
disorder that causes severe lung damage & nutritional deficiencies - Affects cells that produces mucus, sweat, saliva, & digestive juices → secretions become thick & sticky
- Cause: loss of function of the CFTR gene (3-bp deletion F508del & 1,900 other mutations such as G542X, G551D, N1301K, R117H, W1282X, 1717- 1G>A)
- Molecular tests for mutation detection: RFLP, PCR-RFLP, HA, temporal-gradient gel electrophoresis, SSCP, SSP-PCR, cleavase, bead array technology, & direct sequencing
CYSTIC FIBROSIS
- Group of mono-oxygenase enzymes
localized to the ER - Present in high concentrations in the liver & small intestine → enzymes metabolize & detoxify compounds
(drugs) - Polymorphisms affect the metabolism of hormones, caffeine,
chemotherapeutic drugs, antidepressants, & oral contraceptives:
o Tests are used to predict the response to drugs - Detection of polymorphisms: allele-specific PCR
- Screening tests: microarray, bead array, sequencing
CYTOCHROME P-450
CONDITIONS THAT DO NOT FOLLOW
MENDELIAN RULES OF INHERITANCE:
a. Mitochondrial gene mutations
b. Genomic imprinting
c. Gonadal mosaicism
d. Nucleotide-repeat expansion disorders
e. Multifactorial inheritance
- Maternally inherited
- mtDNA
o Circular, 16,569 bp, with 37 genes, 1000-nt control region - Mutations affect energy production → muscles & nervous system
- Molecular methods:
o Large deletions: Southern blot
o Point mutations: PCR-RFLP
MITOCHONDRIAL (mt) GENE
MUTATIONS
mutated mt & normal
mt in the same cell
Heteroplasmy
Genes that control mitochondrial
functions are found in
nuclear genome
- Only 1 copy of a gene in an individual (either from mother or father) is expressed, while the other copy is suppressed
o Example: mules (male donkey x female horse) & hinnies (male horse x female donkey) - Cause: transcriptionally silencing through histone/DNA modification
- Genetic disorders: 1 or other allele of a gene is lost (uniparental disomy)
GENOMIC IMPRINTING
- Generation of new mutations in germline cells → giving rise to
eggs/sperm carrying the mutation which then becomes a heritable
phenotype - Expected when phenotypically normal
parents have more than 1 affected child - Example: osteogenesis imperfecta
GONADAL MOSAICISM
- Nucleotide repeats, such as STRS (1-10 bp repeating units) can expand in length during DNA replication & meiosis
NUCLEOTIDE-REPEAT EXPANSION DISORDER
- expansions of STR w/3-bp repeating units in the
gene sequence
o Fragile X syndrome
o Huntington disease
o Idiopathic congenital central hypoventilation syndrome (CCHS)
Triplet-repeat mutations
- CGG expansion (up to >2,000 repeats) in the noncoding region 5’ to
the FMR-1 gene - Symptoms (increase in severity with each generation): learning disorders & mental retardation (IQ~20), long face, large ears, macroorchidism
- Detection:
o Karyotyping
o PCR
o Southern blot
o Capillary electrophoresis
Fragile X Syndrome
- CAG expansion (9-37 repeats to 38-86 repeats) in the huntingtin structural
gene (4p16.3) - Symptoms: impaired judgment, slurred speech, difficulty in swallowing, chorea, personality changes,
depression, mood swings, unsteady
gait, intoxicated appearance - Detection:
o Standard PCR methods
o Capillary electrophoresis
Huntington Disease
- Gene mutations in PHOX2b gene in chromosome 4: insertion of multiple
alanine residues - Inadequate breathing while asleep, hypoventilation while awake
- Occurs in association with an intestinal disorder (Hirschsprung disease) & symptoms of ANS dysregulation/dysfunction
- Detection:
❖PCR w/32P-labeled primer & polyacrylamide gel electrophoresis
❖Standard PCR & agarose gel electrophoresis
Idiophatic Congenital Central Hypoventilation Syndrome (CCHS)
- Disorders (& normal conditions) controlled by multiple genetic &
environmental factors
(nutritional/chemical exposures) - Phenotypes: conditioned by the no. of controlling genes inherited
- Detection:
o HR-array methods
o NGS - Interpretation:
o Databases (ClinVar & dbSNP) - Prognostic & diagnostic value of gene mutation analysis:
o Annotation of demographics (ethnicity/gender, lifestyles)
MULTIFACTORIAL INHERITANCE
