Amino Acid Disorders

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Disease Name Homocystinuria
Alternate name(s) Cystathionine beta-synthase deficiency
Acronym CBS deficiency
Disease Classification Amino Acid Disorder
Variants Yes
Variant name Pyridoxine-responsive type (the majority of cases are unresponsive to pyridoxine)
Symptom onset Childhood
Symptoms Ectopia lentis, vascular occlusive disease, seizures, malar flush, osteoporosis, possible decreased pigmentation of hair, skin and iris, skeletal abnormalities including genu valgum, pectus excavatum, pes cavus and marfanoid habitus. Some patients have failure to thrive and short stature. Mental retardation is possible.
Natural history without treatment Mental retardation is common but not invariable. Vascular disease, stroke and psychiatric abnormalities.
Natural history with treatment Decrease of thromboembolic accidents which may decrease incidence of sequelae including mental retardation, ectopia lentis, seizures and psychiatric abnormalities. Normal IQ is possible and typical of the pyridoxine-responsive variant.
Treatment Pyridoxine supplementation, dietary restriction of methionine with supplementation of L-cysteine, betaine supplementation. Consider folate and vitamin B12 supplementation.
Other N/A
Physical phenotype Ectopia lentis, decreased pigmentation, malar flush, osteoporosis, skeletal abnormalities and marfanoid habitus
Inheritance Autosomal recessive
General population incidence 1:200,000 – 300,000
Ethnic differences Yes
Population Irish, U.S New England
Ethnic incidence 1:50,000
Enzyme location Lymphocytes, fibroblasts and liver
Enzyme Function Degradation of homocysteine
Missing Enzyme Cystathionine beta-synthase
Metabolite changes Increased methionine in blood, increased homocystine in urine, increased total homocysteine in blood.
Gene CBS gene
Gene location 21q22.3
DNA testing available Yes
DNA testing detail Numerous mutations have been detected. Most prevalent mutations are G307S and I278T. Most patients are compound heterozygotes.
Prenatal testing Enzyme assay in cultured amniocytes (CVS not possible)
MS/MS Profile N/A
Genetests Link
Support Group National Coalition for PKU and Allied Disorders

Children Living with Inherited Metabolic Diseases
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