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GeneticDisorders-II

lecture 26 wilson

QuestionAnswer
biochemical pathway of PKU Phe converted to Tyr via enzyme phenylalanine hydroxylase (PAH), which is defective or absent in PKU pts. results in increased Phe levels and very low Tyr levels (melanin precursor)
inheritance pattern of PKU autosomal recessive, 1/12,000 births affected
clinical features of PKU pt mousy odor, severe MR (if not treated after 6 mo), fair complexion (no Tyr, no melanin), eczema, ataxia (cerebellum), nl facial features, no HSM
maternal PKU teratogenic effects of Phe when mom doesn't have good dietary control. results in 75%-90% of children having MR, microcephaly and congenital heart dz in 15%
galactosemia 1/60,000 AR dz with founder effect in Irish populations, classic form = most commonly due to defect in galactose-1-P uridyl transferase (GALT)
clinical features of galactosemia v/d, neonateal jaundice, hepatomegaly, cataracts from deposition in eyes, MR, infections ("pts are huge Petri dishes full of sugar")
diagnosing/tx of galactosemia direct enzyme assay, presence of non-glucose reducing sugar in urine // remove galactose from diet and avoid cataracts and liver damage; gonadal failure, ataxia and speech disorders are inevitable
anatomic changes of galactosemia that's untreated organomegaly, fatty changes and fibrosis of liver (due to inflammatory response), cataracts
Tay Sachs dz lysosomal-storage AR dz occurring in 1/30 Ashkenazi Jews, mutation in alpha subunit of hexosaminidase A due to frameshift mutation; inability to degrade GM2 gangliosides resulting in lipidosis
clinical features of Tay Sachs dz membranous cytoplasmic bodies by EM, cherry red spot in retina, blindness, motor and mental deterioration, death usually by 2 y/o
Neimann Pick dz types A & B sphingomyelinase deficiency resulting in sphingomyelin accumulation; type A - complete absence of enzyme = visceral & neural accumulation, death by 3 y/o // type B - low enzyme amt, survive to be adults with fatty liver changes
Neimann Pick dz type C chol accumulation due to NPC-1 gene mutation, terminal axons and dendrites degenerate; phenotype: hydrops fetalis, neonatal hepatitis, ataxia, supranuclear palsy (disconjugate gaze), organomegaly, dysarthria
Gaucher dz most common lysosomal-storage dz, glucocerebrosidase mutation causing accumulation in phagocytes; type I - some activity, into adulthood, Jewish predilection // type II - not Jews, die early = no activity // type III - intermediate, juvenile involvement
histologic changes of Gaucher dz macrophages are filled with glucocerebrosides, have fibrillary cytoplasm that looks like "crumpled tissue paper;" can affect CNS, spleen and skeletal systems
mucopolysaccharidoses (MPS) Hurler and Hunter syndromes, no lysosomal enzymes to degrade GAGs so they accumulate within cells; phenotype: cloudy corneas, MR, HSM, CV involvement, coarse facial features, skeletal deformities, joint stiffness
Hurler syndrome (MPS I) AR dz, no alpha-L-iduronidase = can't break down dermatan and heparan sulfate, HSM by 6-24 mo, usually die from valve regurgitation then cardiac arrest, cubitus valgus
Hunter syndrome (MPS II) ONLY lysosomal storage dz that's X-linked, dermatan and heparan sulfate not degraded, no CNS involvement or corneal clouding [Hunters are usually males, have to be able to see well]
glycogen storage diseases von Gierke, McArdle, Pompe
vonGierke dz type I is hepatic form = HM with cirrhosis, hypoglycemia, weakness b/c glycogen can't be cleaved to release free glucose
McArdle dz type V is myopathic form, absent muscle glycogen phosphorylase causes hypotonia, muscle cramps, weakness due to low energy output
Pompe dz type II is lysosomal storage dz AND glycogen storage dz resulting in profound cardiomyopathies and organomegaly. cardiomyocyte lysosome are packed full
alkaptonuria inborn error of metabolism, lack of homogenistic oxidase causing acid to accumulate; phenotype: dark urine, ochronosis, degenerative arthropathy
neurofibromatosis benign defect in regulation of cell growth around neurons and in the neural sheath with typical whorled configuration histologically, genes are NF1 and NF2, AD with 100% penetrance and variable expressivity
neurofibromatosis type I 1/3000, half are new mutations, mild-severe sx from cafe-au-lait spots to malignant neurosarcomas, Lisch nodules - pigmented hamartomas of iris, axillary speckling
neurofibromatosis type II acoustic neurofibromatosis, 1 in 40-50,000; unique bilat neoplasms in auditory canal, meningiomas, ependymal gliomas, non-neoplastic transformations into Schwannosis, glial hamartomas, etc. NF2 or merlin is tumor suppressor gene that's mutated
Created by: sirprakes on 2011-10-02



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