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enzyme deficiencies pt 1

Allelic Heterogeneity same locus can have several different types of clinical presentation Ex. Cystic Fibrosis
Locus Heterogeneity multiple loci associated with one condition. Ex. Retinitis Pigmentosa, Hyperphenylalaninemia
Phenotypic Heterogeneity Ex Hyperphenylalaninemia leading to Classical PKU, Variant PKA, and non-PKU
Phenotypic Heterogeneity due to modifier gene defect in monogenetic disorders Apolipoprotien E gene affects onset of Alzheimers. β-thalassemia patients who also inherit one α-globin null gene = α-globin:β-globin is too high – more severe presentation … if α-globin is also low = less severe presentation
Aminoacidopathies Hyperphenylalaninemia
Purine metabolism defect Lesch-Nyhan Syndrome
Lysosomal storage defects Tay-Sachs disease, Mucopolysaccharidosis, I-cell disease
Mutations impairing binding and metabolism of cofactors Homocystinuria
Other Enzyme Defects Alpha 1-Antitripsin Deficiency
Receptor Protein Defect disease Familial Hypercholesterolemia
Transport defect CF
Disorders of Structural Proteins Duchenne and Becker Muscular Dystrophy, Osteogenesis Imperfecta and Ehlers-Danlos Syndrome
Neurodegenerative Disorders Alzheimer Disease, Huntington Disease, Fragile X syndrome, Myotonic Dystrophy, Fredreich Ataxia, mtDNA Diseases
The first Enzyme defect disease to be studied Alkaptonuria
Single Mutation leading to multiple enzyme defects due to same cofactor, common modifying enzymes, abnormal organelle, or sharing common subunit
Alkaptonuria is a metabolism defect of tyrosine
Alkaptonuria enzyme deficiency Homogentisic oxidase
Alkaptonuria substrate accumulation Homogentisic acid
Alkaptonuria age of onset 40s
Signs of Alkaptonuria darkening of connective tissues (onchronosis), darkening of urine on air exposure, diaper staining, arthritis
Alkaptonuria treatment restric phenylalanine and tyrosine from diet
Hyperphenylalaninemia is a metabolism defect of Pheylalanine Hydroxylase (PAH) or deficiency of tetrahydrobiopterin (BH4)
Hyperphenylalaninemias include all disorders where Phenylalanine accumulates in the blood
Phenylalanine hydroxylase converts Phenylalanine to tyrosine
Classic PKU is when PAH enzyme gene has a defect and leads to accumulation of Phe in body fuids. Phe is then metabolized by alternative pathways to make ketoacids that are excreted in the urine
High Phe and phenylketones results in CNS damage leading to retardation if untreated, a musty odor, and fair skin from lack of melanin
Classic PKU is treated by newbork heelprick and sweat test screening and diet modification
In classic PKU phe levels are less than 1mM and PAH activity is less than 1%
Non PKU hyperphenylalaninemia has some residual activity of PAH greater than 1% and high plasma phe concentrations (.120mM - .4mM) and results in minimal brain damage.
Diet restriction of Phe is not required in non PKU
Variant hyperphenylalaninemia results from defective dihydropteridine reductase which can’t convert BH2 back to BH4 which is a needed cofactor for PAH.
Variant PKU is treated with dietary restriction and replacement of BH4, serotonin, and catecholamine, and Ldopa and 5-hydrocytryptophan
Variant PKU patients can show profound neurological abnormality despite a low Phe diet
BH4 is a cofactor for Phe Hydroxylase, Tyr Hydroxylase, and Trp Hydroxylase
Tyr hydroxylase and Trp hydroxylase need BH4 for synthesis of serotonin and catecholamine. Loss of which leads to irreversible brain damage
Created by: splashgreen