Sunday, June 22, 2008

Progeria

The Progeria
From Wikipedia, the free encyclopedia

Progeria (Greek, "old age") refers specifically to Hutchinson-Gilford Progeria syndrome.

Hutchinson-Gilford Progeria syndrome is an extremely rare condition in which physical aspects of aging are greatly accelerated, and few affected children live past age 13. About 1 in 8 million babies are born with this condition. It is a genetic condition, but occurs sporadically and is usually not inherited in families.

Scientists are particularly interested in progeria because it reveals clues about the normal process of aging

Symptoms

The earliest symptoms include failure to thrive (FTT) and a localized scleroderma-like skin condition.

As the child ages past infancy, additional conditions become apparent. Limited growth, alopecia, and a distinctive appearance with small face and jaw and pinched nose all are characteristic of progeria.

The people diagnosed with this disease usually have small, fragile bodies like those of elderly people.

Later the condition causes wrinkled skin, atherosclerosis and cardiovascular problems
CauseHutchinson-Gilford Progeria Syndrome (HGPS) is a childhood disorder caused by mutations in one of the major architectural proteins of the cell nucleus.

Unlike most other "accelerated aging diseases" (such as Werner's syndrome, Cockayne's syndrome or xeroderma pigmentosum), progeria is not caused by defective DNA repair. Because the "accelerated aging" diseases display different aspects of aging, but never every aspect, they are often called "segmental progerias".

Diagnosis

Diagnosis is suspected according to signs and symptoms, such as skin changes, abnormal growth, and loss of hair. It can be confirmed through a genetic test

TreatmentNo treatments have been proven effective. Most treatment focuses on reducing complications such as cardiovascular disease, such as heart bypass surgery or low-dose aspirinChildren may also benefit from a high-calorie diet.

Growth hormone treatment has been attempted

A type of anti-cancer drug, the farnesyltransferase inhibitors (FTIs), have been proposed, but their use has been mostly limited to animal models. A phase II clinical trial using the FTI Lonafarnib began in May 2007

Prognosis

There is no known cure. Few people with progeria exceed 13 years of age.

At least 90% of patients die from complications of atherosclerosis, such as heart attacks or strokesMental development is not affected.

The development of symptoms is comparable to aging at a rate six to eight times faster than normal, although certain age-related conditions do not occur.

Specifically, victims show no neurodegeneration or cancer predisposition.

They also do not develop "wear and tear" conditions commonly associated with aging, like cataracts and osteoarthritis

Epidemiology

One study from the Netherlands has shown an incidence of 1 in 4 million births. Currently, there are 48 cases in the world.

Approximately 100 cases have been formally identified in medical historyClassical Hutchinson–Gilford Progeria Syndrome is not passed on from parent to child, because most affected children don't live long enough to have children themselves. It is usually caused by a new (sporadic) mutation during the division of the cells that create unfertilized egg or sperm.

In diseases caused by recessive genes, a person with one normal and one disease gene will be normal.

But in diseases caused by dominant genes, a person with one normal and one disease gene will have the disease.

Because Hutchinson–Gilford Progeria Syndrome is dominant, healthy parents can't pass it on to their children

However, there are milder cases in which either the gene is not expressed in parents, or a different gene is responsible for a different form of progeria, and healthy parents can pass on their children.

Three families have been identified as having more than one child with the disease. The first was a family in India that has five children with progeria, two of which are now deceased.

The eldest daughter with progeria is 19 years old, and their eldest son with progeria is 17, both having survived longer than typical among people with progeria.

Their other living child with progeria is 7. The family was a subject of a 2005 Bodyshock documentary entitled The 80 Year Old Children.

In 2006, the Vandersweets, a family in Belgium, who already had one child diagnosed with progeria, were informed that their second child also had the disease

The third case is a family that lives in Aguacatan in Guatemala. The family consist of 3 children. 1,7 and 18 years old. The 7 and 18 year old both have been diagnosed with Progeria, the infant still is uncertain.

Research areas

Several discoveries have been made that have led to greater understanding and perhaps eventual treatment

A 2003 report in Nature said progeria may be a de novo dominant trait. It develops during cell division in a newly conceived child or in the gametes of one of the parents. It is caused by mutations in a LMNA (Lamin A protein) gene on chromosome

1. One of the authors, Leslie Gordon, was a physician who didn't know anything about progeria, until her own son, Sam, was diagnosed at 21 months. Gordon and her husband, pediatrician Scott Berns, founded the Progeria Research Foundation

Lamin ANuclear lamina is a protein scaffold around the edge of the nucleus that helps organize nuclear processes such as RNA and DNA synthesis.

Prelamin A contains a CAAX box at the C-terminus of the protein (where C is a cysteine and A is any aliphatic amino acids).

This ensures that the cysteine is farnesylated, and this allows Prelamin A to bind membranes, specifically the nuclear membrane. After Prelamin A has been localized to the cell nuclear membrane the C-terminal amino acids, including the farnesylated cysteine, are cleaved off by a specific protease.

The resulting protein is now Lamin A, is no longer membrane-bound and carries out functions inside the nucleus.

In HGPS the recognition site that the enzyme requires for cleavage of Prelamin A to Lamin A is mutated.

Lamin A cannot be produced and Prelamin A builds up on the nuclear membrane, causing a characteristic nuclear blebbing.

This results in the premature aging symptoms of progeria, although the mechanism connecting the misshapen nucleus to the symptoms is not known.

A study which compared HGPS patient cells with the skin cells from LMNA young and elderly human subjects found similar defects in the HGPS and elderly cells, including down-regulation of certain nuclear proteins, increased DNA damage and demethylation of histone leading to reduced heterochromatin.

Nematodes over their lifespan show progressive lamin changes comparable to HGPS in all cells but neurons and gametes.These studies suggest that lamin A defects contribute to normal aging.

Mouse model of progeria

A mouse model of progeria exists, though in the mouse the LMNA prelamin A is not mutated, but instead ZMPSTE24, the specific protease that is required to remove the C-terminus of Prelamin A is missing.

Both cases result in the build up of farnesylated Prelamin A on the nuclear membrane and in the characteristic nuclear LMNA blebbing.

Fong et al use a farnesyl transferase inhibitor (FTI) in this mouse model to inhibit protein farnesylation of Prelamin A. Treated mice had greater grip strength, lower likelihood of rib fracture and may live longer than untreated mice.

This method does not directly 'cure' the underlying cause of progeria. This method prevents Prelamin A going to the nucleus in the first place so no Prelamin A can build up on the nuclear membrane, but equally there is no production of normal Lamin A in the nucleus.

Luckily Lamin A does not appear to be essential, indeed mouse models in which the genes for Prelamin A and C are knocked out show no symptoms.

This also shows that it is the build up of Prelamin A in the wrong place, rather than the loss of the normal function of Lamin A that causes the disease.

History

Progeria was first described in 1886 by Jonathan Hutchinsonand also described independently in 1897 by Hastings Gilford.The condition was later named Hutchinson-Gilford Progeria syndrome (HGPS).

source : http://en.wikipedia.org/wiki/Progeria
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