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CAG trinucleotide repeats; gene on chromosome 4

Huntington's disease
-autosomal dominant
-depression, dementia, choreiform mvmnts, caudate atrophy, decreased GABA and decreased ACh
-symptoms between 20-50 yo


Fibrillin gene mutation

Marfan's syndrome
-autosomal dominant
-connective tissue disorder affecting skeleton, heart, eyes
-tall, long extremities, pectus excavatum, hyperextensive joints, arachnodactyly
-cystic medial necrosis of aorta --> aortic incompetence, dissecting aorta, berry aneurysms; floppy mitral valve
-subluxation of lenses


inheritance pattern of the MEN syndromes (multiple endocrine neoplasias)

autosomal dominant
-MEN 2A and 2B are associated with ret gene


cafe au lait spots, neural tumors, Lisch nodules (pigmented iris hamartomas), skeletal disorders (ie scoliosis), optic pathway gliomas

Neurofibromatosis type 1 = von Recklinghausen's disease
-autosomal dominant
-on chrom 17


Bilateral acoustic schwannomas, juvenile cataracts
-what disorder is this?
-what's its mode of inheritance?
-what gene is mutated and on what chromosome?

Neurofibromatosis type 2
-autosomal dominant
-NF2 gene on chromosome 22


Tuberous Sclerosis
-mode of inheritance?

-autosomal dominant
-incomplete penetrance and variable presentation
-Findings: facial lesions (adenoma sebaceum), hypopigmented ash-leaf spots, coritcal and retinal hamartomas, seizures, MR, renal cysts, renal angiomyolipomas, cardiac rhabdomyomas, increased incidence of astrocytomas


ash leaf spots (hypopigmented lesions on skin) + cardiac rhabdomyomas (+other possible symptoms too...)

Tuberous sclerosis


Deletion of VHL gene on chromosome 3

von Hippel-Lindau disease
-autosomal dominant
-deletion of VHL gene = tumor suppressor gene; get constitutive expression of HIF (transcription factor) and activation of angiogenic growth factors
-hemangioblastomas of retina/cerebellum, medulla
-50% of pts develop multiple bilateral renal cell carcinomas and other cancers


List the X-linked recessive disorders

"Be Wise, Fool's GOLD Heeds Silly Hope"
-Bruton's agammaglobulinemia
-Wiskott-Aldrich syndrome
-Fabry's disease
-G6PD deficiency
-Ocular albinism (general albinism = aut recessive!)
-Lesch-Nyhan syndrome
-Duchenne's (and Becker's) muscular dystrophy
-Hunter's Syndrome
-Hemophilia A and B
...also, Fragile X....


meconium ileus in a newborn. think:

-Cystic fibrosis
-Hirschsprung's disease


CFTR gene mutation; mode of inheritance? Function of gene normally?

Cystic Fibrosis
-autosomal recessive
-CFTR gene codes for transmembrane protein that puts Cl from cell into lumen of pancreatic ducts and into lumen of airways; Na follows Cl into lumen, and water follows Na. But, with CFTR defect (abnormal protein folding), decreased water into lumen --> thick mucus

-mucus plugs lungs, pancreas, liver..


most common lethal genetic disease of Caucasians?

cystic fibrosis


recurrent pulmonary infections + malabsorption + caucasian child? Think:

cystic fibrosis


Why are males with CF infertile?

bilateral absence of vas deferens


Treatment for CF pts?

-N-acetylcysteine (inhaled; loosens mucus plugs)
-antibiotics (even fluoroquinolone in kids)
-fat soluble vitamins: A, D, E, K
-pancreatic enzymes


Longest known human gene?

Dystrophin gene (DMD) --> mutated in Duchenne's and Becker's muscular dystrophy


Defect affecting the methylation and expression of the FMR1 gene and trinucleotide repeat of CGG?

Fragile-X syndrome
-X-linked defect
-2nd most common cause of genetic MR
-MR, enlarged testes, long face, large jaw, large everted ears, autism, mitral valve prolapse


What are the 4 trinucleotide repeat expansion diseases (and what's being repeated)?

"Tri Hunting for my Fried Eggs (X)"
1) Huntington's disease (CAG)
2) Myotonic dystrophy (CTG)
3) Friedrich's ataxia (GAA)
4) Fragile X (CGG)
--> all may show anticipation!


flat facies, epicanthal folds, excessive skin at nape of neck, gap between 1st 2 toes, duodenal atresia, congenital heart disease

Down's syndrome


What does may a 1st trimester ultasound of a fetus with trisomy 21 show?

increased nuchal translucency


decreased alpha-fetoprotein
increased beta-hCG
decreased estriol
increased inhibin A

Down's syndrome


decreased alpha-fetoprotein
decreased beta-hCG
decreased estriol
normal inhibin A

Edward's syndrome (trisomy 18)


MR, rocker-bottom feet, small jaw, low-set ears, clenched hands, congenital heart disease

Edward's syndrome (trisomy 18)


Pregnancy quad screen results in Patau's syndrome (trisomy 13)

Normal alpha-fetoprotein, beta-hCG, estriol, inhibin A


MR, rocker-bottom feet, small eyes, cleft lip/palate, holoprosencephaly (single mid-line eye), polydactyly, congenital heart disease

Patau's syndrome (trisomy 13)


Which chromosomes are commonly involved in Robertsonian translocations?

13, 14, 15, 21, 22


MR, microcephaly, high-pitched crying, epicanthal folds, VSD (or other cardiac abnormalities)

Cri-du-chat syndrome (congenital microdeletion of short arm of chromosome 5)


distinctive "elfin" facies, MR, hypercalcemia (and sensitivity to vitamin D), well-developed verbal skills and very friendly with strangers, CV problems

William's syndrome (think of Will ferrel in "Elf")
-d/t congenital microdeletion of long arm of chromosome 7 (including elastin gene)


90% of pts with DiGeorge syndrome have a deletion where?

22q11 deletion


Symptoms of microdeletion at chromosome 22q11:

variable, but includes CATCH-22:
-Cleft palate
-Abnormal facies
-Thymic aplasia (prob with development of 3rd and 4th branchial pouches) --> T-cell deficiency
-Cardiac defects
-Hypocalcemia (d/t parathyroid aplasia)

*see in 90% of DiGeorge pts
*see in Velocardiofacial syndrome (palate, facial, and cardiac defects)