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Homocystinuria due to CBS Deficiency

Table of Contents

Homocystinuria due to CBS Deficiency

Classic Homocystinuria; Cystathionine Beta-Synthase Deficiency; CBS Deficiency; Homocystinuria due to Cystathionine Beta-Synthase Deficiency

Homocystinuria due to CBS deficiency is a genetic condition that results from poor metabolism of folate (also called vitamin B9), due to a lack of working enzyme called cystathionine beta-synthase (CBS). Explore symptoms, causes, and genetics of this condition.

Folic acid crystals

Image by W. Oelen/Wikimedia

Summary

Homocystinuria

Image by National Eye Institute

Homocystinuria

Homocystinuria

Image by National Eye Institute

What Is Homocystinuria due to CBS Deficiency?

Homocystinuria due to CBS deficiency is an inherited disorder in which the body is unable to correctly use the amino acid, homocysteine, one of the building blocks of protein. This form of homocystinuria is caused by a genetic mutation in the CBS gene, which leads to low levels or absence of an enzyme called cystathionine beta-synthase (CBS). When CBS is absent or not working right, homocysteine and other toxic chemicals build up in the blood and urine. Symptoms of this disorder include poor growth and slow weight gain in infancy. Additional symptoms include nearsightedness, dislocation of the lens of the eye, an increased risk of blood clots, and developmental problems.

Homocystinuria due to CBS deficiency is inherited in an autosomal recessive pattern. It is diagnosed by newborn screening, or later in life by blood and urine testing. There are two types of homocystinuria due to CBS deficiency. One type responds to treatment with vitamin B6 and the other one does not. Other treatments for this disorder include a protein-restricted diet, betaine treatment, and other supplements. With early treatment, individuals with this condition can have normal growth and development.

Source: Genetic and Rare Diseases (GARD) Information Center

Causes

Mutation

Image by AJC1

Mutation

Mutation in the DNA

Image by AJC1

What Causes Homocystinuria due to CBS Deficiency?

CBS gene, which lead to missing or low levels of the enzyme, cystathionine beta-synthase (CBS). When this enzyme is missing or there is not enough of it, the body cannot process homocysteine. When this happens, homocysteine and another amino acid, methionine, build up in the blood. It is not clear why this build up of homocysteine and methionine is toxic to the body.

Source: Genetic and Rare Diseases (GARD) Information Center

CBS Gene

Ideogram of human chromosome 21

Image by Office of Biological and Environmental Research of the U.S. Department of Energy Office of Science, the Biological and Environmental Research Information System, Oak Ridge National Laboratory.

Ideogram of human chromosome 21

Selected genes, traits, and disorders associated with the chromosome listed; (blue and violet) regions reflecting the unique patterns of light and dark bands seen on human chromosomes stained to allow viewing through a light microscope; (red) the centromere, or constricted portion, of each chromosome; (yellow) chromosomal regions that vary in staining intensity and sometimes are called hererochromatin (meaning “different color”); (lines between yellow) variable regions, called stalks, that connect a very small chromosome arm (a “satellite”) to the chromosome.

Image by Office of Biological and Environmental Research of the U.S. Department of Energy Office of Science, the Biological and Environmental Research Information System, Oak Ridge National Laboratory.

CBS Gene: Cystathionine Beta-Synthase

Normal Function

The CBS gene provides instructions for making an enzyme called cystathionine beta-synthase. This enzyme acts in a chemical pathway and is responsible for using vitamin B6 to convert building block of proteins (amino acid) called homocysteine and serine to a molecule called cytathionine. Another enzyme then converts cystathionine to the amino acid cysteine, which is used to build proteins or is broken down and excreted in urine. Additionally, other amino acids, including methionine, are produced in this pathway.

Health Conditions Related to Genetic Changes

Homocystinuria

More than 150 mutations that cause homocystinuria have been identified in the CBS gene. Most of these mutations change single amino acids in cystathionine beta-synthase. The most common mutation substitutes the amino acid threonine for the amino acid isoleucine at position 278 in the enzyme (written as Ile278Thr or I278T). Another common mutation, which is the most frequent cause of homocystinuria in the Irish population, replaces the amino acid glycine with the amino acid serine at position 307 (written as Gly307Ser or G307S). These mutations disrupt the normal function of cystathionine beta-synthase. As a result, homocysteine and other potentially toxic compounds build up in the blood, and homocysteine is excreted in urine. Researchers have not determined how excess homocysteine leads to the signs and symptoms of homocystinuria.

Other Names for This Gene

beta-thionase
CBS_HUMAN
HIP4
methylcysteine synthase
serine sulfhydrase

Genomic Location

The CBS gene is found on chromosome 21.

Source: MedlinePlus Genetics

Inheritance

autosomal recessive pattern of inheritance

Image by Thomas Shafee and TheVisualMD

autosomal recessive pattern of inheritance

Newborn autosomal recessive pattern of inheritance

Image by Thomas Shafee and TheVisualMD

How Is Homocystinuria due to CBS Deficiency Inherited?

CBS gene in every cell have mutations. To have the disorder, a person must have a mutation in both copies of the responsible gene in each cell. There is nothing either parent can do, before or during a pregnancy, to cause a child to have this.

People with this disorder inherit one mutation from each of their parents. The parents, who each have one mutation, are known as carriers. Carriers of an autosomal recessive disorder typically do not have any signs or symptoms (they are unaffected). When two carriers of an autosomal recessive condition have children, each child has a:

25% chance to have the disorder
50% chance to be an unaffected carrier like each parent
25% chance to be unaffected and not be a carrier

Source: Genetic and Rare Diseases (GARD) Information Center

Symptoms

Myopia / Normal Vision

Myopia / Normal Vision

Interactive by Creative Commons

Myopia / Normal Vision

Myopia / Normal Vision

1) Myopia 2) Normal Vision

Interactive by Creative Commons

What Are the Signs and Symptoms of Homocystinuria due to CBS Deficiency?

Nearsightedness
Dislocation of the lens of the eye
Skeletal abnormalities
Osteoporosis
Blood clots
Seizures
Intellectual disability
Psychiatric issues

The symptoms of the vitamin B6 responsive form of homocystinuria are generally milder than those of the non-responsive form. Some people with homocystinuria do not develop symptoms until adulthood. One of the only symptoms in adults with homocystinuria may be blood clots.

Source: Genetic and Rare Diseases (GARD) Information Center

Diagnosis

Newborn Screening of blood Samples

Image by TheVisualMD

Newborn Screening of blood Samples

Newborn Screening of blood Samples

Image by TheVisualMD

How Is Homocystinuria Diagnosed?

Most states in the US test for homocystinuria due to CBS deficiency at birth by newborn screening. A baby that has a positive newborn screening test needs to have additional blood testing to look for high levels of homocysteine and methionine in the blood. Genetic testing can also be helpful for diagnosis.

A child or an adult with dislocation of the lens of the eye may also get tested for homocystinuria using blood and urine testing. In addition, a child or adult who has a blood clot, especially at an early age, may also get tested for homocystinuria.

Source: Genetic and Rare Diseases (GARD) Information Center

Homocysteine Test

Homocysteine Test

Also called: Homocyst(e)ine, Homocysteine Cardiac Risk

A homocysteine test measures the level of homocysteine in your blood. High levels may mean a vitamin deficiency, heart disease, or an inherited disorder.

Homocysteine Test

Also called: Homocyst(e)ine, Homocysteine Cardiac Risk

A homocysteine test measures the level of homocysteine in your blood. High levels may mean a vitamin deficiency, heart disease, or an inherited disorder.

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Use the slider below to see how your results affect your health.
mg/L
0.68
2.02
Your result is Normal.
Homocysteine is an amino acid found in most cells of the body, in trace amounts. Normally, homocysteine levels are low, because it is constantly turned into other substances your body needs.
Related conditions
A homocysteine test may be used to:
- Find out if you're lacking vitamin B6, B12, or folic acid. These vitamins break down homocysteine. So if you don't have enough of them, your homocysteine levels will increase. A homocysteine test may be done with a blood test to measure your vitamin B levels.
- Help diagnose homocystinuria. Homocystinuria is a rare, genetic disease that prevents your body from using a certain amino acid to make important proteins. Symptoms usually show up in the first year of life, but they may not appear until childhood or later. Common symptoms include problems with eyesight, blood clots, and weak bones. In the U.S., most newborns have a routine screening test to check for homocystinuria.
- Better understand your risk for heart attack or stroke if you already have an increased risk. Your health care provider may order a homocysteine test if you have been diagnosed with heart or blood vessel disease or if you have conditions that increase your risk for heart and blood vessel disease, such as:
  High blood pressure
  High cholesterol
  Diabetes
Medical experts don't recommend routine homocysteine testing to screen for heart disease risk in everyone. That's because researchers aren't sure how much homocysteine levels affect heart and blood vessel diseases. And so far, studies have shown that lowering homocysteine levels doesn't reduce the risk of heart attack or stroke.
You may need this test if you have symptoms that suggest you lack vitamin B12 or folic acid. The symptoms may be very mild to severe and may include:
- Dizziness
- Fatigue and/or weakness
- Headache
- Heart palpitations (racing or pounding heart)
- Changes in the color of your skin or fingernails
- Sores on your tongue or in your mouth
- Tingling or numbness in your hands, feet, arms, and/or legs
Your provider may order this test if you have a high risk for low levels of vitamin B12 or folic acid because you:
- Have malnutrition.
- Are an older adult. Older people often can't absorb enough vitamin B12 from food.
- Have alcohol use disorder or a drug addiction.
Your provider may recommend this test if you:
- Have had a heart attack or stroke
- Have one or more conditions that increase your risk for heart attack or stroke, such as high LDL "bad" cholesterol or high blood pressure
A high homocysteine level may be a sign that:
- You are not getting enough vitamin B12 or folic acid in your diet.
- You (or your child) have homocystinuria. You will probably need more testing to rule out or confirm a diagnosis of homocystinuria.
- You may have a higher risk of heart disease, stroke, or other blood vessel disorders.
Higher than normal homocysteine levels may also happen with other conditions, such as osteoporosis, chronic kidney disease, hypothyroidism, or Alzheimer's disease or other types of dementia.
If your homocysteine levels are high, it doesn't always mean you have a medical condition that needs treatment. Your results may be affected by:
- Your age. Homocysteine levels may get higher as you get older.
- Your sex. Males usually have higher homocysteine levels than females, but levels in females increase after menopause.
- Smoking
If you have questions about your results, talk with your provider.
1. Homocysteine Test: MedlinePlus Lab Test Information [accessed on Sep 30, 2018]
2. Homocysteine [accessed on Sep 30, 2018]
3. 706994: Homocyst(e)ine | LabCorp [accessed on Sep 30, 2018]
4. Homocysteine Blood Test [accessed on Sep 30, 2018]
5. Fontanarosa, P., & Christiansen, S. (2009, April 01). Laboratory Values. AMA Manual of Style. Ed. [accessed on Sep 30, 2018]
6. https://www.drkarafitzgerald.com/2017/04/04/low-homocysteine-concern/ [accessed on Sep 30, 2018]

Normal reference ranges can vary depending on the laboratory and the method used for testing. You must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

Additional Materials (8)

CRP And Homocysteine Inflammation Markers, How Do They Relate To Coronary Artery Disease? - Dr. Lyel

Video by EmpowHER/YouTube

This browser does not support the video element.

What Is Inflammation?

Inflammation is the body's response to damage. It takes many forms. Chronic inflammation is common in overweight and obese people, because their fat cells manufacture damaging substances that trigger a reaction from the immune system's white blood cells. Keeping track of a key biomarker for inflammation, C-reactive Protein or CRP, helps doctors determine whether an overweight patient is at risk for such conditions as heart disease, dementia, diabetes, cancers, and more.

Video by TheVisualMD

Homocystinuria Infographic

Video by HCU Network/YouTube

The Homocysteine Factor

Video by hcyfactor/YouTube

Homocysteine

homocysteine molecule (L-isomer).

Image by Ben Mills and Jynto

Homocysteine

Homocysteine is a non-proteinogenic amino acid. It is a homologue of the amino acid cysteine, differing by an additional methylene (-CH2-) group. It is biosynthesized from methionine, and can be recycled into methionine or converted into cysteine with the aid of B-vitamins. While detection of high levels of homocysteine has been linked to cardiovascular disease, lowering homocysteine levels may not improve outcomes.

Image by TheVisualMD

Fasting for a Blood Test | WebMD

Video by WebMD/YouTube

Fasting Plasma Glucose

Fasting Plasma Glucose - The fasting plasma glucose (FPG) test, also known as the fasting blood sugar test, measures blood sugar levels and is used to diagnose diabetes.

Image by TheVisualMD

2:12

CRP And Homocysteine Inflammation Markers, How Do They Relate To Coronary Artery Disease? - Dr. Lyel

EmpowHER/YouTube

1:57

What Is Inflammation?

TheVisualMD

3:57

Homocystinuria Infographic

HCU Network/YouTube

3:23

The Homocysteine Factor

hcyfactor/YouTube

Homocysteine

Ben Mills and Jynto

Homocysteine

TheVisualMD

0:50

Fasting for a Blood Test | WebMD

WebMD/YouTube

Fasting Plasma Glucose

TheVisualMD

Newborn Screening Tests

Newborn Blood Spot Screening

Also called: Newborn Blood Spot Test, NBS, Neonatal Heel Prick Test

Right after birth, babies need many important tests and procedures to ensure their health. Newborn screening detects disabling or possibly fatal conditions early enough so that treatments can reduce disability or death from that condition. The screening generally includes a variety of blood tests and a hearing test.

Newborn Blood Spot Screening

Also called: Newborn Blood Spot Test, NBS, Neonatal Heel Prick Test

Right after birth, babies need many important tests and procedures to ensure their health. Newborn screening detects disabling or possibly fatal conditions early enough so that treatments can reduce disability or death from that condition. The screening generally includes a variety of blood tests and a hearing test.

{"label":"Blood spot screening reference range","scale":"lin","step":0.5,"hideunits":true,"items":[{"flag":"normal","label":{"short":"In-range (normal)","long":"In-range (normal)","orientation":"horizontal"},"values":{"min":0,"max":1},"text":"An in-range (also called negative, normal, or low risk) result means that your baby probably does not have a condition detected by blood spot screening. Babies with in-range results do not need more testing.","conditions":[]},{"flag":"borderline","label":{"short":"Borderline","long":"Borderline","orientation":"horizontal"},"values":{"min":1,"max":2},"text":"A borderline (also called inconclusive or medium risk) result means that your baby\u2019s screening results fall somewhere between an in-range and out-of-range result. Babies with borderline results need more screening or testing.","conditions":[]},{"flag":"abnormal","label":{"short":"Out-of-range (abnormal)","long":"Out-of-range (abnormal)","orientation":"horizontal"},"values":{"min":2,"max":3},"text":"An out-of-range (also called positive, abnormal, or high risk) result means that your baby might have the condition detected by the screening test. Babies with out-of-range results need more testing.","conditions":["Disorders detected by newborn screening"]}],"value":0.5}[{"normal":0},{"borderline":0},{"abnormal":0}]
Use the slider below to see how your results affect your health.
Your result is In-range (normal).
An in-range (also called negative, normal, or low risk) result means that your baby probably does not have a condition detected by blood spot screening. Babies with in-range results do not need more testing.
Related conditions
1. Newborn Screening. Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) [accessed on Jan 09, 2019]
2. What is newborn screening? - Genetics Home Reference - NIH [accessed on Jan 09, 2019]
3. Newborn screening tests: MedlinePlus Medical Encyclopedia [accessed on Jan 09, 2019]
4. Newborn blood spot test - NHS [accessed on Jan 09, 2019]
5. Frequently Asked Questions About Newborn Bloodspot Screening | National Newborn Screening and Global Resource Center [accessed on Jan 09, 2019]
6. New York | Baby's First Test | Newborn Screening | Baby Health [accessed on Jan 09, 2019]
7. Newborn Screening | Lab Tests Online [accessed on Jan 09, 2019]
8. Newborn Screening Tests (for Parents) [accessed on Jan 09, 2019]

Additional Materials (24)

Newborn screening

Newborn baby feet and letters of A, T, C G.

Image by www.genome.gov

Newborn Screening

Newborn screening tests use a dried blood sample collected during the first week after birth to measure the presence of disease biomarkers (a measurable substance or characteristic that is indicative of a disease).

Image by National Human Genome Research Institute (NHGRI)

Infographic Newborn screening system

Infographic Newborn screening system

Image by Colorado Department of Public Health and Environment

The Public Health Lab: Newborn Screening

Video by mnhealth/YouTube

Cystic Fibrosis Newborn Screening.

Video by Nemours/YouTube

Newborn Screening and Fabry Disease: What We Know and Don't Know

Video by Rare Disease Report/YouTube

Newborn Hearing Screening - Boys Town National Research Hospital

Video by BoysTownHospital/YouTube

Beyond the Blood Spot: Newborn Screening for Hearing Loss and Critical Congenital Heart Disease

Video by Centers for Disease Control and Prevention (CDC)/YouTube

What is newborn screening? Animated video for parents.

Video by PerkinElmer, Inc./YouTube

Newborn Screening

Video by Mayo Clinic/YouTube

Cystic Fibrosis Newborn Screening Information for Pediatricians

Video by Nemours/YouTube

Newborn screening test: guidelines for care providers

Video by Sunnybrook Hospital/YouTube

Newborn Screening: A Personal Story

Video by March of Dimes/YouTube

Your Newborn's Health Screening

Video by KK Women's and Children's Hospital/YouTube

Cystic Fibrosis Newborn Screening | Cincinnati Children's

Video by Cincinnati Children's/YouTube

How Newborn Hearing Screening Helps Children

Video by Washington State Department of Health/YouTube

X-Linked Adrenoleukodystrophy: Newborn Screening in Males

Video by The WSRGN/YouTube

HGP10 Symposium: Whole Genome Sequencing in Newborn Screening - Jeff Botkin

Video by National Human Genome Research Institute/YouTube

Expanding Newborn Screening to X-ALD — What Else Might We Find and How Will This Impact Patients?

Video by UW Video/YouTube

Beyond the Blood Spot: Newborn Screening for Hearing Loss and Critical Congenital Heart Disease

Video by Centers for Disease Control and Prevention (CDC)/YouTube

California Department of Public Health's Newborn Screening Program

Video by CA Public Health/YouTube

SCID

Video by Immune Deficiency Foundation/YouTube

Phenylketonuria (PKU)

Video by Nutricia Metabolics/YouTube

WHAT IS MLD? Metachromatic Leukodystrophy explained to all

Video by YourekaScience/YouTube

Newborn screening

www.genome.gov

Newborn Screening

National Human Genome Research Institute (NHGRI)

Infographic Newborn screening system

Colorado Department of Public Health and Environment

1:52

The Public Health Lab: Newborn Screening

mnhealth/YouTube

5:50

Cystic Fibrosis Newborn Screening.

Nemours/YouTube

3:37

Newborn Screening and Fabry Disease: What We Know and Don't Know

Rare Disease Report/YouTube

1:54

Newborn Hearing Screening - Boys Town National Research Hospital

BoysTownHospital/YouTube

14:52

Beyond the Blood Spot: Newborn Screening for Hearing Loss and Critical Congenital Heart Disease

Centers for Disease Control and Prevention (CDC)/YouTube

3:19

What is newborn screening? Animated video for parents.

PerkinElmer, Inc./YouTube

2:25

Newborn Screening

Mayo Clinic/YouTube

8:16

Cystic Fibrosis Newborn Screening Information for Pediatricians

Nemours/YouTube

2:45

Newborn screening test: guidelines for care providers

Sunnybrook Hospital/YouTube

3:25

Newborn Screening: A Personal Story

March of Dimes/YouTube

9:30

Your Newborn's Health Screening

KK Women's and Children's Hospital/YouTube

2:42

Cystic Fibrosis Newborn Screening | Cincinnati Children's

Cincinnati Children's/YouTube

3:02

How Newborn Hearing Screening Helps Children

Washington State Department of Health/YouTube

6:20

X-Linked Adrenoleukodystrophy: Newborn Screening in Males

The WSRGN/YouTube

35:56

HGP10 Symposium: Whole Genome Sequencing in Newborn Screening - Jeff Botkin

National Human Genome Research Institute/YouTube

1:00:03

Expanding Newborn Screening to X-ALD — What Else Might We Find and How Will This Impact Patients?

UW Video/YouTube

1:04:18

Beyond the Blood Spot: Newborn Screening for Hearing Loss and Critical Congenital Heart Disease

Centers for Disease Control and Prevention (CDC)/YouTube

3:24

California Department of Public Health's Newborn Screening Program

CA Public Health/YouTube

7:55

SCID

Immune Deficiency Foundation/YouTube

7:07

Phenylketonuria (PKU)

Nutricia Metabolics/YouTube

5:57

WHAT IS MLD? Metachromatic Leukodystrophy explained to all

YourekaScience/YouTube

Prognosis

Prognosis Icon

Image by mcmurryjulie/Pixabay

Prognosis Icon

Image by mcmurryjulie/Pixabay

What Is the Long-Term Outlook for People with Homocystinuria due to CBS Deficiency?

When treatment is started early, children with this disorder can have normal growth and development, and can avoid the complications seen with this disorder. However, it is still possible that they could develop a dislocation of the lens of the eye or a blood clot. Sometimes the blood clots can be very serious and cause organ damage. In addition, some people may develop osteoporosis in adulthood as a result of this disorder.

Source: Genetic and Rare Diseases (GARD) Information Center

Statistics

Orthographic map of Qatar centered at 25° N, 51° E.

Image by Addicted04/Wikimedia

Orthographic map of Qatar centered at 25° N, 51° E.

Orthographic map of Qatar centered at 25° N, 51° E. Official territory. Claimed territories.

Image by Addicted04/Wikimedia

How Common Is Homocystinuria due to CBS Deficiency?

Approximately 1 in 200,000 to 1 in 300,000 people in the US has homocystinuria due to CBS deficiency. In other countries, the prevalence is higher. In Quatar, about 1 in 1800 people has this disorder and in Norway, about 1 in 6400 people has it. World-wide, it is thought that about 1 in 150,000 people has homocystinuria due to CBS deficiency.

Source: Genetic and Rare Diseases (GARD) Information Center

Related HealthJournals

Homocystinuria

Homocystinuria refers to a group of inherited disorders in which the body is unable to process amino acids properly. This leads to increased amounts of homocysteine and other amino acids in the blood and urine. Explore symptoms, causes, and genetics of this condition.

Homocystinuria due to MTHFR Deficiency

Homocystinuria due to MTHFR deficiency is a genetic condition that results from poor metabolism of folate (also called vitamin B9), due to a lack of working enzyme called methylenetetrahydro-folate reductase (MTHFR).

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Homocystinuria due to CBS Deficiency

Homocystinuria due to CBS deficiency is a genetic condition that results from poor metabolism of folate (also called vitamin B9), due to a lack of working enzyme called cystathionine beta-synthase (CBS). Explore symptoms, causes, and genetics of this condition.

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