Hartnup Disease

Hartnup Disease Definition

It is an acquired metabolic disease that has an impact on the metabolism of essential vitamins in the body. It affects the transfer of some amino acids like Histidine and Tryptophan in the kidneys and small intestine.

Hartnup Disease History

The disorder was first noticed in the Hartnup family of London and described in 1956 by Baron et al. In this eight-member family, as many as four members displayed Cerebellar Ataxia and Aminoaciduria, a rash similar to Pellagra. These were actually found to be the symptoms of Hartnup Disease. The condition owes its name to the family that it was first noticed in.

Hartnup Disease Symptoms

Most individuals with this condition do not display any major health problems other than small vitamin deficiencies. Acute cases of this disease may give rise to symptoms like,

  • Frequent skin rashes
  • Mental disorders
  • Difficulties in muscle coordination

The deficiency of Nicotinamide, a kind of Vitamin B, is the most substantial insufficiency resulting from this condition. Extreme deficit of Vitamin B may also lead to problems like

  • Neurological difficulties
  • Skin problems
  • Tremors
  • Poor coordination
  • Frequent episodes of muscular fatigue

Some affected individuals may also develop a condition known as Chronic Dermatitis. It is characterized by itchiness and redness all over the body, which tend to worsen when the skin is exposed to direct rays of the sun. In rare cases, Hartnup Disease may give rise to a potentially debilitating problem known as Dementia (a condition involving deterioration of intellectual faculties, such as concentration, judgment and memory). An untreated case of acute Hartnup Disease, first appearing in infant stages, may lead to irreversible mental retardation.

Hartnup Disease in Children

As aforesaid, this condition is typically asymptomatic (symptomless) in most individuals. When the symptoms of this disease appear, they usually manifest themselves as early as in childhood. Some of the main symptoms of Hartnup Disease in children may involve:

  • Changes in mood
  • Diarrhea
  • Neurological problems, like abnormal muscle tone
  • Short height
  • Red, scaly rashes, particularly when skin is unprotected from direct sunlight
  • Unorganized body movements
  • Sensitivity to light (Photosensitivity)

Hartnup Disease Causes

This is an inherited condition. It has been found to be an autosomal recessive disease that arises in children who have both parents carrying a mutated copy of a specific gene known as SLC6A19. The disorder can seriously affect a child who inherits a copy of this defective gene from both parents.

In healthy individuals, the dietary amino acids are decomposed by the intestines and transported to the kidneys and the liver. These organs metabolize the acids into essential vitamins and proteins, which are absorbed into the bloodstream. The presence of a mutated SLC6A19 hampers the ability of the kidneys and intestines to metabolize amino acids present in consumed foods. The acids are then ejected as waste through the urine of the affected person.

Hartnup Disease is probably the most common metabolic disorder involving amino acids. It generally arises in children who are between 3 and 5 years old.

Hartnup Disease and Genetics

This condition is obtained as an autosomal recessive trait. In 2004, the gene SLC6A19, was identified as the causative factor of this disorder. It is a chloride-independent and sodium-dependent neutral amino acid transporter that is predominately expressed in the intestine and kidneys. It is situated on band 5p15.33 and Chromosome 5.

Hartnup Disease Diagnosis

Doctors usually diagnose and cure this disorder with tests of urine samples. A urine test helps detect any increase in the level of “neutral” amino acids. In some patients, blood samples may be screened to diagnose any deficiencies in vitamin levels. If the doctor suspects other causes for the symptoms, complex genetic testing procedures and brain imaging scans may be recommended.

Biochemical tests are available for detection of the causative gene for this condition.

Hartnup Disease Treatment

Individuals suffering from comparatively moderate symptoms of this disease, treatment involves daily intake of supplements rich in Vitamin B and Nicotinamide as well as following diets rich in protein. Most neurological symptoms resolve themselves naturally when vitamin levels come back to their usual range. Daily intake of 50-300mg Nicotinamide and Nicotinic acid has been found to provide relief if neurological symptoms or skin problems arise at any time.

As aforesaid, exposure to sunlight is a major trigger factor for Dermatitis. Hence, patients of this condition may be instructed to use sunscreen (of factor 15 or over) and wear protective garments while going outdoors. If acute rashes continue to arise in patients, doctors may prescribe topical creams to relieve the discomforting skin symptoms.

If patients suffer from psychiatric problems or mood swings, psychiatric treatment should be provided to them. Medicines like mood stabilizers or antidepressants may be used in such cases.

Hartnup Disease Prognosis

Most individuals with this condition can expect to live as normally as others and without any disability. It is only in rare cases that the disease has been found to result in acute neurological problems and even deaths of sufferers. A positive thing about this condition is the fact that its attacks reduce with advancing age.

Hartnup Disease Life Expectancy

Patients affected with this disorder are found to have a normal life expectancy. The disease is not found to sghorten the lifespan in any way, except in rare cases. Usually, neurological symptoms are reversible. In rare cases, however, these may turn serious or life-threatening.

Hartnup Disease Complications

Generally, the condition does not give rise to any complications. Even when complications occur, they may include:

  • Psychiatric problems
  • Uncoordinated movements
  • Permanent changes in skin pigmentation
  • Skin rashes

Hartnup Disease Prevention

In some cases, this condition can be prevented with the aid of genetic counseling. Following a diet rich in protein may also help prevent deficiencies in amino acid that lead to the appearance of the symptoms.

If you suspect yourself to be having symptoms of this disease and also have a family history condition, make an appointment with your doctor immediately. Medical counseling is also required for people who have Hartnup Disease patients in their family and are planning a pregnancy.






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