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GeneticDisorders-II
lecture 26 wilson
| Question | Answer |
|---|---|
| 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 |
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sirprakes
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