Progeria
Progeria is an extremely rare autosomal dominant genetic disorder in which symptoms resembling aspects of aging are manifested at a very early age. Progeria is one of several progeroid syndromes. Those born with progeria typically live to their mid-teens to early twenties. It is a genetic condition that occurs as a new mutation, and is rarely inherited, as carriers usually do not live to reproduce children. Although the term progeria applies strictly speaking to all diseases characterized by premature aging symptoms, and is often used as such, it is often applied specifically in reference to Hutchinson–Gilford progeria syndrome.
Signs and symptoms
Children with progeria usually develop the first symptoms during their first few months of life. The earliest symptoms may include a failure to thrive and a localized scleroderma-like skin condition. As a child ages past infancy, additional conditions become apparent usually around 18–24 months. Limited growth, full-body alopecia, and a distinctive appearance are all characteristics of progeria. Signs and symptoms of this progressive disease tend to become more marked as the child ages. Later, the condition causes wrinkled skin, atherosclerosis, kidney failure, loss of eyesight, and cardiovascular problems. Scleroderma, a hardening and tightening of the skin on trunk and extremities of the body, is prevalent. People diagnosed with this disorder usually have small, fragile bodies, like those of elderly people. The head is usually large in relation to the body, with a narrow, wrinkled face and a beak nose. Prominent scalp veins are noticeable, as well as prominent eyes. Musculoskeletal degeneration causes loss of body fat and muscle, stiff joints, hip dislocations, and other symptoms generally absent in the non-elderly population. Individuals usually retain typical mental and motor development.Cause
Progeria is caused by mutations that weaken the structure of the cell nucleus, making normal cell division difficult. The histone mark H4K20me3 is involved in Hutchinson-Gilford Progeria syndrome caused by de novo mutations that occurs in a gene that encodes lamin A. Lamin A is made but isn't processed properly. This poor processing creates an abnormal nuclear morphology and disorganized heterochromatin. Patients also don't have appropriate DNA repair, and they also have increased genomic instability.In normal conditions, the LMNA gene codes for a structural protein called prelamin A, which undergoes a series of processing steps before attaining its final form, called lamin A. Prelamin A contains a “CAAX”where C is a cysteine, an aliphatic amino acid, and X any amino acid. This motif at the carboxyl-termini of proteins triggers three sequential enzymatic modifications. First, protein farnesyltransferase catalyzes the addition of a farnesyl moiety to the cysteine. Second, an endoprotease that recognizes the farnesylated protein catalyzes cleavage of the peptide bond between the cysteine and -aaX. In the third step, isoprenylcysteine carboxyl methyltransferase catalyzes methylation of the carboxyl-terminal farnesylcysteine. The farnesylated and methylated protein is transported through a nuclear pore to the interior of the nucleus. Once in the nucleus, the protein is cleaved by a protease called zinc metallopeptidase STE24, which removes the last 15 amino acids, which includes the farnesylated cysteine. After cleavage by the protease, prelamin A is referred to as lamin A. In most mammalian cells, lamin A, along with lamin B1, lamin B2 and lamin C, makes up the nuclear lamina, which provides structural support to the nucleus.
Before the late 20th century, research on progeria yielded very little information about the syndrome. In 2003, the cause of progeria was discovered to be a point mutation in position 1824 of the LMNA gene, which replaces a cytosine with thymine. This mutation creates a 5' cryptic splice site within exon 11, resulting in a shorter than normal mRNA transcript. When this shorter mRNA is translated into protein, it produces an abnormal variant of the prelamin A protein, referred to as progerin. Progerin's farnesyl group cannot be removed because the ZMPSTE24 cleavage site is lacking from progerin, so the abnormal protein is permanently attached to the nuclear rim. One result is that the nuclear lamina does not provide the nuclear envelope with enough structural support, causing it to take on an abnormal shape. Since the support that the nuclear lamina normally provides is necessary for the organizing of chromatin during mitosis, weakening of the nuclear lamina limits the ability of the cell to divide. However, defective cell division is unlikely to be the main defect leading to progeria, particularly because children develop normally without any signs of disease until about one year of age. Farnesylated prelamin A variants also leads to defective DNA repair, which may play a role in the development of progeria. Progerin expression also leads to defects in the establishment of fibroblast cell polarity, which is also seen in physiological aging.
To date over 1,400 SNPs in the LMNA gene are known. They can manifest as changes in mRNA, splicing, or protein amino acid sequence.
Progerin may also play a role in normal human aging, since its production is activated in typical senescent cells.
Unlike other "accelerated aging diseases", progeria may not be directly caused by defective DNA repair. These diseases each cause changes in a few specific aspects of aging, but never in every aspect at once, so 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. These symptoms normally start appearing by one year of age. A genetic test for LMNA mutations can confirm the diagnosis of progeria.Treatment
No treatment has yet proven effective. Most treatment options have focused on reducing complications with coronary artery bypass surgery and low-dose aspirin.Growth hormone treatment has been attempted. The use of Morpholinos has also been attempted in mice and cell cultures 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, 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.
Farnesyltransferase inhibitors 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 occur 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.
Studies of sirolimus, an mTOR Inhibitor, demonstrate 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. These results have been observed only in vitro and are not the results of any clinical trial, although it is believed that the treatment might benefit HGPS patients.
The Investigational New Drug application for delivery of lonafarnib has been accepted, but not yet approved by the US Food and Drug Administration. Therefore, it can only be used in certain clinical trials. Until treatment with FTIs is thoroughly tested in progeria children in clinical trials, its effects on humans cannot be known, although its effects on mice seem to be positive. A 2012 clinical trial found that it improved weight gain and other symptoms of progeria. A further clinical trial in 2018 points to significantly lower mortality rates ~ treatment with lonafarnib alone compared with no treatment ~ at a median post-trial follow-up time span of 2.2 years.
Prognosis
As there is no known cure, few people with progeria exceed 13 years of age. At least 90 percent 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 average 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 conditions that are commonly associated with aging, such as cataracts and osteoarthritis.
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 delivered healthy offspring.
Epidemiology
A study from the Netherlands has shown an incidence of 1 in 20 million births. According to the Progeria Research Foundation, there are currently about 161 known cases in the world. Hundreds of cases have been reported in medical history since 1886. However, the Progeria Research Foundation believes there may be as many as 150 undiagnosed cases worldwide.Classical Hutchinson–Gilford progeria syndrome is usually caused by a sporadic mutation taking place during the early stages of embryo development. It is almost never passed on from affected parent to child, as affected children rarely live long enough to have children themselves.
There have been only two cases in which a healthy person was known to carry the LMNA mutation that causes progeria. These carriers were identified because they passed it on to their children. One family from India has five children with progeria, though not the classical HGPS type. This family was the subject of a 2005 Bodyshock documentary titled The 80 Year Old Children. The Vandeweert family of Belgium has two children, Michiel and Amber, with classic HGPS.
History
Progeria was first described in 1886 by Jonathan Hutchinson. It was also described independently in 1897 by Hastings Gilford. The condition was later named Hutchinson–Gilford progeria syndrome. Scientists are interested in progeria partly because it might reveal clues about the normal process of aging.Etymology
The word progeria comes from the Greek words "pro", meaning "before" or "premature", and "gēras", meaning "old age".Society and culture
Notable cases
In 1987, fifteen-year-old Mickey Hays, who had progeria, appeared along with Jack Elam in the documentary I Am Not a Freak. Elam and Hays first met during the filming of the 1986 film The Aurora Encounter, in which Hays was cast as an alien. The friendship that developed lasted until Hays died in 1992, age 20. Elam said, "You know I've met a lot of people, but I've never met anybody that got next to me like Mickey."Harold Kushner's 1978 book When Bad Things Happen to Good People, which explores God and the problem of evil, was written in response to his 14-year-old son's death due to progeria.
Margaret Casey, a 29-year-old progeria victim believed to be the oldest survivor of the premature aging disease, died on Sunday May 26, 1985. Casey, a free-lance artist, was admitted to Yale-New Haven Hospital Saturday night May 25th with respiratory problems, which caused her death.
Sam Berns, an American activist who was the subject of the HBO documentary Life According to Sam. Berns also gave a TEDx talk titled My Philosophy for a Happy Life on December 13th, 2013.
Hayley Okines was an English progeria patient who spread awareness of the condition.
Popular culture
Perhaps one of the earliest influences of progeria on popular culture occurred in the 1922 short story "The Curious Case of Benjamin Button" by F. Scott Fitzgerald. The main character, Benjamin Button, is born as a 70-year-old man and ages backwards; it has been suggested that this was inspired by progeria. Charles Dickens may also have described a case of progeria in the Smallweed family of Bleak House, specifically in the grandfather and his grandchildren, Judy and twin brother Bart.The condition has also been featured in multiple films. In the 1983 film The Hunger, progeria was the focus of study by Susan Sarandon's character, Dr. Sarah Roberts. The 1984 film The Three Wishes of Billy Grier stars Ralph Macchio as a teenager who tries to fulfill his wishes before he dies from the disease. The 1996 movie Jack deals with the eponymous character who has a genetic disorder similar to progeria and the difficulties he faces fitting into society. In 2009, the movie was remade by Bollywood as Paa and starred Amitabh Bachchan, Vidya Balan and Abhishek Bachchan.
Research
Several discoveries have been made that have led to greater understandings and perhaps eventual treatment for this disease.A 2003 report in Nature said that progeria may be a de novo dominant trait. It develops during cell division in a newly conceived zygote or in the gametes of one of the parents. It is caused by mutations in the LMNA gene on chromosome 1; the mutated form of lamin A is commonly known as progerin. One of the authors, Leslie Gordon, was a physician who did not know anything about progeria until her own son, Sam, was diagnosed at 22 months. Gordon and her husband, pediatrician Scott Berns, founded the Progeria Research Foundation.
Lamin A
is a major component of a protein scaffold on the inner edge of the nucleus called the nuclear lamina that helps organize nuclear processes such as RNA and DNA synthesis.Prelamin A contains a CAAX box at the C-terminus of the protein. This ensures that the cysteine is farnesylated and 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, 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 symptoms of progeria, although the relationship between the misshapen nucleus and the symptoms is not known.
A study that compared HGPS patient cells with the skin cells from young and elderly normal 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 are associated with normal aging.
Mouse model
A mouse model of progeria exists, though in the mouse, the LMNA prelamin A is not mutated. Instead, ZMPSTE24, the specific protease that is required to remove the C-terminus of prelamin A, is missing. Both cases result in the buildup of farnesylated prelamin A on the nuclear membrane and in the characteristic nuclear LMNA blebbing. Fong et al. use a farnesyl transferase inhibitor in this mouse model to inhibit protein farnesylation of prelamin A. Treated mice had greater grip strength and 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 from going to the nucleus in the first place so that no prelamin A can build up on the nuclear membrane, but equally, there is no production of normal lamin A in the nucleus. Lamin A does not appear to be necessary for life; mice in which the Lmna gene is knocked out show no embryological symptoms. This implies that it is the buildup of prelamin A in the wrong place, rather than the loss of the normal function of lamin A, that causes the disease.
It was hypothesized that part of the reason that treatment with an FTI such as alendronate is inefficient is due to prenylation by geranylgeranyltransferase. Since statins inhibit geranylgeranyltransferase, the combination of an FTI and statins was tried, and markedly improved "the aging-like phenotypes of mice deficient in the metalloproteinase Zmpste24, including growth retardation, loss of weight, lipodystrophy, hair loss, and bone defects".