Homocysteinuria

Alternative names: This conditions is also sometimes referred to as Cystathionine beta-synthase deficiency or Homocysteinemia

The compound homocysteine is normally not found in the blood or urine in noteworthy amounts.  Homocysteinuria is a metabolic disorder resulting in an excessive accumulation of homocysteine in the blood and urine.

Homocysteinuria comes in multiple forms which do not have specific names but are recognized by their symptoms and genetic causes.

Incidence; Causes and Development; Contributing Risk Factors

Homocysteinuria affects roughly 1 in 100,000 people but is much more common in some countries:

• Qatar – 1 in 1,800
• Norway – 1 in 6,400
• Germany – 1 in 17,800
• Ireland – 1 in 65,000

Homocysteinuria is an inherited genetic mutation which requires two copies of the mutated gene in order to develop; with only one affected gene the child will merely become a carrier.  If two carriers have a child there is still a 25% chance the baby will receive a completely normal pair of genes.

The severity of Homocysteinuria may be increased by nutritional and environmental factors.  One example is a high-protein diet, which can cause major complications.

Signs and Symptoms

Symptoms of Homocysteinuria do not usually appear until a child is 3 to 4 years old.  Without early treatment, they can be severe.  Some of the symptoms include:

• Chest deformities
• Flush across the cheeks
• Vision problems (in 80% of cases)
• High arches of the feet
• Tall, thin build and long limbs
• Osteoporosis
• Knock knees (Genu valgum)
• Bone and joint problems
• Intellectual disability
• Mental disorders
• Learning disability (in 50% of cases)

Diagnosis and Tests

If a child exhibits several of the signs and symptoms and/or there is a family history of Homocysteinuria, the following tests can be conducted:

• Amino acid screening
• Genetic testing
• Skeletal X-ray
• Skin biopsy
• Liver biopsy
• Ophthalmic exam

Newborns are now offered blood spot screening once they are 5 days old to check if they have Homocysteinuria.  If the tests come back positive then treatment can be offered immediately.

Treatment and Prevention

Although there is no cure for Homocysteinuria, treatment can be offered to reduce symptom severity and decrease the risk and severity of complications.  This treatment aims to control homocysteine levels in the blood.

Treatments include Vitamin B6, specialized diet, and sometimes medication.  Regular blood tests monitor the amount of homocysteine in a patient's blood.

Vitamin B6 (pyridoxine)
High doses of Vitamin B6 can control levels of homocysteine in around 50% of patients.  This determination can be made using a pyridoxine response assessment; those patients should take supplemental B6 during their entire lives.  Those who do not respond should take supplements B6, B9 (folate) and B12 (cobalamin) their entire lives.

Diet
If vitamin B6 treatment is ineffective, a low-protein diet will be advised with the help of a specialist metabolic dietitian.  This will be specifically tailored to reduce the amounts of methionine released in the body.  Breast milk and baby milk will need to be measured and when the child progresses to solid foods a dietitian will provide guidance as to what is suitable.  Children with Homocysteinuria will need to follow a specific diet for the rest of their lives.

Medication
Betaine (sometimes referred to as Trimethylglycine or TMG) may be prescribed to aid the body in removing excess homocysteine.

Prevention
It is important for known carriers to use preventive measures when planning a family.  These include genetic counselling and prenatal diagnosis of Homocysteinuria.  Chorionic villus sampling or amniocentesis can be used for testing.

Prognosis; Complications; Seek medical attention if...

Early detection and treatment can help those with Homocysteinuria to live a normal, healthy life.  If treatment is started soon enough it may even be possible to prevent intellectual disabilities and some of the other complications.

If left untreated, a child's symptoms are very likely to worsen and become severe.  For this reason all newborns are screened for Homocysteinuria in some health districts.

Elevated homocysteine levels are a risk factor for all kinds of vascular disease including strokes and heart ailments.  Homocysteinuria can result in mental retardation and seizures.

The most serious (and potentially fatal) complications arise from blood clots.  Elevated homocysteine levels are a risk factor for all kinds of vascular disease including strokes and heart ailments, especially Carotid Stenosis.

Homocysteinuria can also result in serious intellectual disability, mental retardation and seizures.

A dislocated lens in the eye can seriously affect vision and in some cases surgery may be needed.  Some of the other possible complications include:

• Coronary artery disease
• Thromboembolism
• Osteoporosis
• Fatty infiltration of the liver
• Mitral valve prolapse
• Pancreatitis

It is important to seek medical attention if you or a family member shows any signs of this disorder, especially if there is a family history of Homocysteinuria.