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Disorders with Atypical Pattern of Inheritance - Single Gene Disorders 2

Dr. Yakubovskyy - March 19, 2012 Semester 4, Mini 3
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6 month old infant presents severe mental retardation and hypopigmentation. In your investigations you find that there are high levels of serum phenylalanine.
What disease do you suspect?
What enzyme is defective?
What is the associated inheritance pattern?
PKU
→ phenylalanine hydroxylase
→ AR
What amino acid becomes essential in PKU?
tyrosine
6 month old infant presents severe mental retardation and a mousy urine smell. What is the disease? What makes the smell mousy?
PKU
→ accumulation of phenylacetic acid
What test is used to screen newborns for PKU?
heel prick test
What is the tx for pts diagnosed with PKU?
Phenylalanine restriction in the diet starting from postnatal period
Expectant mothers homozygous for PKU: low-phenylalanine diet
What is the enzyme deficient in galactosemia?
As a result, what accumulates?
galactose-1-phosphate uridyl transferase (GALT, 9p)
→ galactose-1-phosphate
Infant presents with failure to thrive with vomiting and diarrhea following milk ingestion. He also appears jaundice with hepatomegaly. Within a few weeks he develops cataracts.
What is your likely dx?
galactosemia
What type of bacterial septicemia are galactosemia pts at risk for?
E. coli septicemia
What cells are tested for GALT activity in the dx of galactosemia?
RBCs
What is the tx of galactosemia?
milk free diet
What chromosome is the CFTR gene on?
chr. 7
What channel does CFTR inhibit?
ENac
How does a mutated CFTR gene effect mucous viscosity?
↑ mucous viscosity
How does a mutated CFTR channel lead to pancreatic duct plugging?
→ ↓ HCO₃⁻ secretions
→ acidic pancreatic duct secretions
→ mucin precipitation
→ plugging
What respiratory tract disorders are CF pts at risk for?
chronic bronchitis, bronchiolitis, bronchiectasis, lung abscesses, sinusitis and sinonasal polyps
Why is there male infertility in CF pts even though spermatogenesis is not affected?
bilateral absence of vas deferens
Why is there female infertility in CF pts?
thick cervical mucus plug and anovulatory cycles
what test is used to screen newborns for CF?
heel prick test
What is the main cause of death of CF pts?
COPD and cor pulmonale
What are common multifactorial diseases in adults?
hypertension, atherosclerosis, DM2, allergic diathesis, psoriasis
What are common multifactorial diseases in children?
pyloric stenosis, cleft lip and palate, congenital heart disease, hypospadias, hirschprung disease
What is the Lyon effect?
random and irreversible inactivation of 2nd X chromosome in females during embryogenesis
What is the most common X-linked disorder?
G6PD deficiency (1:10)
color blindness (1:76)
Why do affected X-link recessive disorder affected men never pass on their disorder to their sons?
They pass their Y to their sons.
All their daughters will be carriers though.
What syndrome is associated with the pseudoautosomal genes on the inactivated X chromosome?
What is the gene?
fragile-X syndrome
FMR1 @ Xq27 → CGG repeat expansion
How does increased CGG repeats in FMR1 lead to mental retardation?
↑ repeats → ↑ gene methylation → altered synaptic activity → mental retardation and physical abnormalities
How many repeats is considered pathological in fragile-X syndrome?
200-4000
How can the physical manifestations of fragile-X syndrome present?
long face
prominent ears
macroorchidism
Fragile-X shows worsening features in each successive generation. What is the phenomenon called?
anticipation
On which chromosome, paternal or maternal, is the Prader-Willi gene expressed?
paternal
On which chromosome, paternal or maternal, is the Angelman gene expressed?
maternal
What does the Prader-Willi code for?
small nuclear riboprotein N
→ expressed in brain and heart
What does the Angelman gene code for?
ubiquitin ligase
→ expressed in brain
What stage of protein synthesis is silenced in genomic imprinting?
transcription
What are the genetic mechanims that can lead to Prader-Willi and Angelman syndromes?
chromosome deletion
uniparental disomy
point mutation
Pt presents with mental retardation, hyperphagia, obesity, and hypogonadism. What do you suspect?
Prader-Willi syndrome
Pt presents with mental retardation, atactic gait, seizure hx, and inappropriate laughter. Possible dx?
Angelman syndrome