Homocystinuria

Homocystinuria is a rare disorder that has an incidence of approximately 1 in 344,000 people in the world population. Read and know all about the causes, symptoms, diagnosis and cure of this syndrome.

Homocystinuria Definition

It is an inherited condition that that has a negative impact on the metabolism of the amino acid known as Methionine. The disease is also known as Cystathionine Beta Synthase (CBS) deficiency.

Homocystinuria Symptoms

Newborn infants with this disorder appear normal and healthy. Symptoms, even if present, are not evident at all in the early stages. They may arise as moderately retarded development or an inability to thrive.

It is usually in the later stages that the symptoms of the condition become apparent. The disorder is especially characterized by increasing visual problems which may lead to its diagnosis.

Some other symptoms of Homocystinuria include:

  • Flush across the cheeks
  • Chest deformities (Pectus Excavatum, Pectus Carinatum)
  • Tall, thin build
  • Knock knees
  • High arches of the feet
  • Spider-shaped fingers (Arachnodactyly)
  • Near-sightedness
  • Long limbs
  • Mental retardation
  • Psychiatric disorders
  • increased risk of thrombosis
  • Atrophy of eye muscles
  • Arterial swelling
  • Glaucoma
  • Seizures

The effects of this disease are apparent in the cardiovascular system, central nervous system, muscles as well as connective tissue.

Several features of Homocystinuria have been found to be similar to Marfan syndrome. Unlike Marfan syndrome, however, the joints tend to be “tight” in Homocystinuria and not “loose”.

Homocystinuria Causes

This is an autosomal recessive condition which signifies that a child needs to acquire the defective gene from both parents to get affected by the problem. That an individual inherits Homocystinuria in an autosomal fashion indicates that the genes involved in the rise of this disease are not situated in the sex chromosomes. That the condition is recessive implies that for a child to be born with the disorder both parents must act as carriers of one copy of the defective gene.

Homocystinuria Diagnosis

The diagnosis of this syndrome usually begins with a thorough physical examination of the affected child. Healthcare providers usually look for a tall, thin stature (Marfanoid stature) in children. Other common signs looked for include:

  • Deformity of the chest
  • Curved spine (scoliosis)
  • Dislocated lens of the eye

If patients are found to suffer from a poor eyesight or double vision, an ophthalmologist should conduct a dilated eye exam to detect ocular problems like nearsightedness or eye lens dislocation. Doctors also check whether the patient suffers from frequent blood clots and shows slightly low IQ and signs of mental retardation or psychiatric illnesses.

Some common diagnostic tests for Homocystinuria involve:

  • Enzyme assay
  • Liver biopsy
  • Genetic testing
  • Skeletal x-ray
  • Standard ophthalmic examination
  • Skin biopsy, with a fibroblast culture
  • Amino acid screening of urine and blood

Homocystinuria Treatment

There is an absence of cure for Homocystinuria as yet. However, certain medicines and an appropriate diet plan can help in managing it. Approximately half of all patients show favorable response to high doses of Pyridoxine (Vitamin B6). Such individuals need to use vitamin B6 supplements for as long as they live.

Homocystinuria Medicine Treatment

A medication known as Trimethylglycine (also referred to as Betaine) is the preferred choice of medicine for most patients. Betaine transforms Homocysteine into Methionine. This reduces the accumulation rate of Homocysteine to a greater extent and allows Methionine to be integrated into the protein reserves of the body.

Homocystinuria Dietary Management

It is important to use Betaine together with a low-methionine diet. This is due to the fact that though the drug continuously converts tiny amounts of homocysteine into methionine, it fails to maintain a fast pace of homocysteine production. Hence, the medication must be used along with the low-methionine diet. Used together, the diet and the medication can prevent accumulation of homocysteine to toxic levels and prevent development of the symptoms of Homocystinuria. Sufferers, who do not respond to Pyridoxine supplements, need to follow this diet.

Both diet and medications need to be supervised properly by a physician experienced in treating Homocystinuria.

Addition of cysteine (an amino acid) in the daily diet, along with a normal dose of folic acid supplement, can also yield effective results. However, mental retardation fails to improve with either medications or a low-methionine diet.

Homocystinuria Prognosis

Although there is no definite cure for Homocystinuria, its symptoms can be relieved to a great extent by Vitamin B6 therapy in about half of all sufferers. Around half of all individuals with this condition can be effectively treated with administration of high doses of vitamin B6 on a regular basis. Patients who respond favorably to this treatment may not require any further treatment. However, they may need to stick to a special diet that is low in protein, methionine and some other amino acids. A low-methionine diet helps reduce the rate of Homocysteine accumulation in the body.

If the diagnosis is conducted while a patient is still young, making him or her quickly follow a low-methionine diet can prevent some of the major complications of the disease such as mental retardation. It is for this reason that some states screen all newborns for Homocystinuria.

Patients suffering from constant elevation in Homocysteine levels in the bloodstream are at high risk of developing blood clots. Development of clots can result in dangerous medical problems and reduce lifespan.

Homocystinuria Complications

As aforesaid, presence of blood clots can give rise to acute complications which can be life-threatening. Dislocation of the eye lenses can severely impair vision with patients requiring Lens replacement surgery for correction. The disease can also lead to mental retardation, which is a serious problem. Retardation, however, can be reduced if the disorder is diagnosed early.

Homocystinuria Prevention

The disease can be prevented by intrauterine diagnosis, which involves culturing of Chorionic Villi or amniotic cells to detect Cystathionine Synthase. An absence of this enzyme confirms Homocystinuria. Couples having a family history of Homocystinuria should undergo genetic counseling before an episode of pregnancy.

If specific genetic mutations are known to be present in parents or family members, samples from amniocentesis or chorionic villus sampling can be used to check for the presence of these mutations.

If you or any family member is displaying symptoms of this condition, immediately get in touch with your health care provider. This is more important for people having a family history of this disease. Medial consultation is also necessary if you are planning to have children and have a family history of Homocystinuria.

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