Progeria

Synonyms

4

Overview

Hutchinson-Gilford progeria syndrome is a genetic condition characterized by the dramatic, rapid appearance of aging beginning in childhood. Affected children typically look normal at birth and in early infancy, but then grow more slowly than other children and do not gain weight at the expected rate (failure to thrive). They develop a characteristic facial appearance including prominent eyes, a thin nose with a beaked tip, thin lips, a small chin, and protruding ears. Hutchinson-Gilford progeria syndrome also causes hair loss (alopecia), aged-looking skin, joint abnormalities, and a loss of fat under the skin (subcutaneous fat). This condition does not disrupt intellectual development or the development of motor skills such as sitting, standing, and walking.

Hutchinson-Gilford progeria syndrome is considered an autosomal dominant condition, which means one copy of the altered gene in each cell is sufficient to cause the disorder. The condition results from new mutations in the LMNA gene, and almost always occurs in people with no history of the disorder in their family

Symptoms

Affected children typically look normal at birth and in early infancy, but then grow more slowly than other children and do not gain weight at the expected rate (failure to thrive). They develop a characteristic facial appearance including prominent eyes, a thin nose with a beaked tip, thin lips, a small chin, and protruding ears. Hutchinson-Gilford progeria syndrome also causes hair loss (alopecia), aged-looking skin, joint abnormalities, and a loss of fat under the skin (subcutaneous fat). This condition does not disrupt intellectual development or the development of motor skills such as sitting, standing, and walking.

Causes

Mutations in the LMNA gene cause Hutchinson-Gilford progeria syndrome.

The LMNA gene provides instructions for making a protein called lamin A. This protein plays an important role in determining the shape of the nucleus within cells. It is an essential scaffolding (supporting) component of the nuclear envelope, which is the membrane that surrounds the nucleus. Mutations that cause Hutchinson-Gilford progeria syndrome result in the production of an abnormal version of the lamin A protein. The altered protein makes the nuclear envelope unstable and progressively damages the nucleus, making cells more likely to die prematurely. Researchers are working to determine how these changes lead to the characteristic features of Hutchinson-Gilford progeria syndrome.

Read more about the LMNA gene.

Prevention

Not knowen.

Diagnosis

Diagnosis is suspected according to signs and symptoms, such as skin changes, abnormal growth, and loss of hair. A genetic test for LMNA mutations can confirm the diagnosis of progeria.

Prognosis

As 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 attack or stroke.

Mental development is not adversely affected; in fact, intelligence tends to be normal to above average. With respect to the features of aging that progeria appears to manifest, the development of symptoms is comparable to aging at a rate eight to ten times faster than normal. With respect to features of aging that progeria does not exhibit, patients show no neurodegeneration or cancer predisposition. They also do not develop the so-called "wear and tear" conditions commonly associated with aging, such as cataracts (caused by UV exposure) and osteoarthritis (caused by mechanical wear).

Although there may not be any successful treatments for progeria itself, there are treatments for the problems it causes, such as arthritic, respiratory, and cardiovascular problems. Sufferers of progeria have normal reproductive development and there are known cases of women with progeria who had delivered healthy offspring.

Treatment

No treatment has proven effective. Most treatment focuses on reducing complications (such as cardiovascular disease) with coronary artery bypass surgery or low-dose aspirin. Children may also benefit from a high-energy diet.

Growth hormone treatment has been attempted. The use of Morpholinos has also been attempted in order to reduce progerin production. Antisense Morpholino oligonucleotides specifically directed against the mutated exon 11–exon 12 junction in the mutated pre-mRNAs were used.

A type of anticancer drug, the farnesyltransferase inhibitors (FTIs), has 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. In studies on the cells another anti-cancer drug, rapamycin, caused removal of progerin from the nuclear membrane through autophagy. It has been proved that pravastatin and zoledronate are effective drugs when it comes to the blocking of farnesyl group production. However, it is important to remember that no treatment is able to cure progeria.

Farnesyltransferase inhibitors (FTIs) are drugs that inhibit the activity of an enzyme needed in order to make a link between progerin proteins and farnesyl groups. This link generates the permanent attachment of the progerin to the nuclear rim. In progeria, cellular damage can be appreciated because that attachment takes place and the nucleus is not in a normal state. Lonafarnib is an FTI, which means it can avoid this link, so progerin can not remain attached to the nucleus rim and it now has a more normal state.

The delivery of lonafarnib is not approved by the US Food and Drug Administration (FDA). Therefore, it can only be used in certain clinical trials. Until the treatment of FTIs is implemented in progeria children we will not know its effects—which are positive in mice.

Pravastatin, traded as Pravachol or Selektine, is included in the family of statins. As well as zoledronate (also known as Zometa and Reclast, which is a bisphosphonate), its utility in HGPS is the prevention of farnesyl group formation, which progerin needs to provoke the disease. Some animal trials have been realized using FTIs or a combination of pravastatin and zoledronate so as to observe whether they are capable of reversing abnormal nuclei.

The results, obtained by blinded electron microscopic analysis and immunofluorescence microscopy, showed that nucleus abnormalities could be reversed in transgenic mice expressing progerin. The reversion was also observed in vivo—cultured cells from human subjects with progeria—due to the action of the pharmacs, which block protein prenylation (transfer of a farnesyl polypeptide to C-terminal cysteine). The authors of that trial add, when it comes to the results, that: "They further suggest that skin biopsy may be useful to determine if protein farnesylation inhibitors are exerting effects in subjects with HGPS in clinical trials".

Unlike FTIs, pravastatin and zoledronate were approved by the U.S. FDA (in 2006 and 2001 respectively), although they are not sold as a treatment for progeria. Pravastatin is used to decrease cholesterol levels and zoledronate to prevent hypercalcaemia.

Rapamycin, also known as Sirolimus, is a macrolide. There are recent studies concerning rapamycin which conclude that it can minimize the phenotypic effects of progeria fibroblasts. Other observed consequences of its use are: abolishment of nuclear blebbing, degradation of progerin in affected cells and reduction of insoluble progerin aggregates formation. All these results do not come from any clinical trial, although it is believed that the treatment might benefit HGPS patients.

A 2012 clinical trial found that the cancer drug Lonafarnib can improve weight gain and other symptoms of progeria.