Primordial has been defined as belonging to or being characteristic of the earliest stages of development of an organism. Therefore, Primordial Dwarfism is a class of disorders where growth delay occurs at the earliest stages of development. Unlike some of the other forms of dwarfism where newborn infants can have average lengths, children with Primordial Dwarfism are born smaller than average and have intrauterine growth retardation (IUGR).
Unlike some of the other conditions described on this website, primordial dwarfism is not a specific diagnosis.
It is in fact a class of disorders to which at least 5 different conditions are currently grouped:
- Russell-Silver syndrome
- Seckel syndrome
- Meier-Gorlin syndrome
- Majewski osteodysplastic primordial dwarfism (MOPD) Types I/III
- MOPD Type II
The Russell-Silver, Seckel and Meier-Gorlin syndromes are relatively well defined entities and we will not discuss them here.
We will limit our discussion to MOPD Type II. Most of the information below can be examined in more detail in Hall et. al (1).
All of the conditions that make up primordial dwarfism are quite rare and very little is known concerning the incidences. For MOPD Type II, we estimate that there are no more than 100 patients in the United States and Canada giving a rough estimate of 1 in 3 million.
Everyone has two copies of a gene called pericentrin (PCNT). MOPDII results when there is a gene change (mutation) in each copy of an individual’s pericentrin gene, causing both copies to be nonfunctional (2).
Probably the most consistent physical characteristic of primordial dwarfism in children is severe intrauterine growth retardation (IUGR). Recognition of the deficiency can occur as early as 13-weeks gestation and it becomes progressively more severe over the length of the pregnancy.
At term, infants with primordial dwarfism typically weigh less than 3 lbs and are less than 16 inches in length. This is about the average size of a 28-week premature neonate. However, some children with genetically confirmed MOPDII have been born larger than this. Adult heights are typically less than 33" and the voice is high pitched.
Face and Skull
- Microcephaly. Head size is proportionate to body size at birth. However, as children grow and develop, the head grows slower than the body and becomes disproportionately small.
- Premature closure of the soft spots (fontanelles) and craniosynostosis
- Prominent nose and eyes. The conspicuous nose may be obvious at birth or it may develop over the first year.
- Small teeth with deficient enamel and increased spaces between them. Small roots in the secondary teeth. Secondary teeth can be missing or lost prematurely.
Arms and Legs:
- disproportionately short forearm in childhood, causing mesomelia
- dislocated radial head with decreased range of motion at the elbows
- dislocated hips and coxa vara at birth
- ligamentous laxity develops with age
Other Characteristics of Primordial Dwarfism:
- fine and relatively sparse hair
- pigmentary changes of the skin, such as acanthosis nigricans
What are the X-Ray Characteristics of Primordial Dwarfism?
In newborns with primordial dwarfism, the X-rays typically do not demonstrate major structural abnormalities, although the pelvis is narrow with small iliac wings and flattened acetabular angles. The long bones may be overtubulated. Eleven rib pairs are sometimes seen, rather than twelve. As children with primordial diagnosis age, the bones appear thin and delicate with progressive metaphyseal widening at the ends of the long bones.
Bone age studies usually show decreased bone age; that is, the skeletal maturation process is slowed in these children and can be delayed 2–5 years behind the actual age.
The differential diagnosis for MOPD II is complex and is done clinically based upon history, physical characteristics, radiographic review and the exclusion of any other physical findings or laboratory abnormalities.
There is also research genetic testing available either through Texas
or Scotland that can help confirm what type of primordial dwarfism an individual has.
Most infants with primordial dwarfism have feeding problems, but it is important that the treating physician lower their expectations of daily growth to at least half that of a typical child.
Small volumes and frequent feeding are typical. Sometimes nasogastric feeding or g-tube feedings are used.
Some patients have structural or myelination abnormalities in the brain. Structural abnormalities have included: enlarged ventricles, abnormal gyral patterns and abnormal corpus callosum.
Precocious puberty has been described in girls with breast development as early as 7 and menarche, or the beginning of periods, at 9 years. Boys do not seem to have precocious puberty.
Renal or kidney anomalies have been described and a renal ultrasound should be done as the diagnosis is being established.
Most of the patients develop farsightedness which requires glasses. Careful ophthalmologic evaluation is indicated at regular intervals.
A vast majority of individuals with MOPDII have had abnormalities in the cerebral vascular system, including moyamoya disease and aneurysms, which can predispose to stroke. Screenings with MRA/CTA of the brain should begin at diagnosis of MOPDII and continue every 12 to 18 months thereafter to permit early detection of these conditions. If diagnosed in the early stages, revascularization and aneurysm treatment can be performed safely and effectively. (3)
Insulin resistance is associated with MOPDII and can often progress to frank diabetes. Yearly screening labs should begin by 5 years of age and include: hemoglobin A1C, insulin levels, fasting blood sugars, liver functions and lipid profiles. The physician should maintain a high degree of suspicion and if any signs or symptoms develop, further testing is indicated. If changes are present, appropriate follow-up and management plans can be implemented. It does appear that these patients respond well to an oral antihyperglycemic medication like metformin. (4)
A yearly CBC should also be obtained as some children, especially post-pubertal girls, have developed anemia. Furthermore, it does appear that baseline platelet counts may be elevated. The clinical significance of this remains to be determined.
- Hall JG, Flora C, Scott CI Jr., Pauli RM, Tanaka KI. Majewski osteodysplastic primordial dwarfism type II (MOPDII): natural history and clinical findings. Am J Med Genet A. 2004 Sep 15;130A(1):55-72.
- Rauch A, Thiel CT, Schindler D, Wick U, Crow YJ, Ekici AB, van Essen AJ, Goecke TO, Al-Gazali L, Chrzanowska KH, Zweier C, Brunner HG, Becker K, Curry CJ, Dallapiccola B, Devriendt K, Dörfler A, Kinning E, Megarbane A, Meinecke P, Semple RK, Spranger S, Toutain A, Trembath RC, Voss E, Wilson L, Hennekam R, de Zegher F, Dörr HG, Reis A. Mutations in the pericentrin (PCNT) gene cause primordial dwarfism. Science. 2008 Feb 8; 319(5864):816-9.
- Bober MB, Khan N, Kaplan J, Lewis K, Feinstein JA, Scott CI Jr, Steinberg GK. Majewski osteodysplastic primordial dwarfism type II (MOPD II): expanding the vascular phenotype. Am J Med Genet A. 2010 Apr;152A(4):960-5.
- Huang-Doran I, Bicknell LS, Finucane FM, Rocha N, Porter KM, Tung YC, Szekeres F, Krook A, Nolan JJ, O'Driscoll M, Bober M, O'Rahilly S, Jackson AP, Semple RK; for the Majewski Osteodysplastic Primordial Dwarfism Study Group. Genetic Defects in Human Pericentrin Are Associated With Severe Insulin Resistance and Diabetes. 2011 Mar;60(3):925-35. Epub 2011 Jan 26.
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All About Genetics
What do you know about your family tree? Have any of your relatives had health problems that tend to run in families? Which of these problems affected your parents or grandparents? Which ones affect you or your brothers or sisters now? Which problems might you pass on to your children?
Thanks to advances in medical research, doctors now have the tools to understand much about how certain illnesses, or increased risks for certain illnesses, pass from generation to generation. Here are some basics about genetics.
Genes and Chromosomes
Each of us has a unique set of chemical blueprints affecting how our body looks and functions. These blueprints are contained in our DNA (deoxyribonucleic acid), long, spiral-shaped molecules found inside every cell. DNA carries the codes for genetic information and is made of linked pieces (or subunits) called nucleotides. Each nucleotide contains a phosphate molecule, a sugar molecule (deoxyribose), and one of four so-called "coding" molecules called bases (adenine, guanine, cytosine, or thymidine). The order (or sequence) of these four bases determines each genetic code.
The segments of DNA that contain the instructions for making specific body proteins are called genes. Scientists believe that human DNA carries about 25,000 protein-coding genes. Each gene may be thought of as a "recipe" you'd find in cookbook. Some are recipes for creating physical features, like brown eyes or curly hair. Others are recipes to tell the body how to produce important chemicals called enzymes (which help control the chemical reactions in the body).
Along the segments of our DNA, genes are neatly packaged within structures called chromosomes. Every human cell contains 46 chromosomes, arranged as 23 pairs (called autosomes), with one member of each pair inherited from each parent at the time of conception. After conception (when a sperm cell and an egg come together to make a baby), the chromosomes duplicate again and again to pass on the same genetic information to each new cell in the developing child. Twenty-two autosomes are the same in males and females. In addition, females have two X chromosomes and males have one X and one Y chromosome. The X and the Y are known as sex chromosomes.
Human chromosomes are large enough to be seen with a high-powered microscope, and the 23 pairs can be identified according to differences in their size, shape, and the way they pick up special laboratory dyes.
Errors in the genetic code or "gene recipe" can happen in a variety of ways. Sometimes information is missing from the code, other times codes have too much information, or have information that's in the wrong order.
These errors can be big (for example, if a recipe is missing many ingredients — or all of them) or small (if just one ingredient is missing). But regardless of whether the error is big or small, the outcome can be significant and cause a person to have a disability or at risk of a shortened life span.
Abnormal Numbers of Chromosomes
When a mistake occurs as a cell is dividing, it can cause an error in the number of chromosomes a person has. The developing embryo then grows from cells that have either too many chromosomes or not enough.
In trisomy, for example, there are three copies of one particular chromosome instead of the normal two (one from each parent). Trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome) are examples of this type of genetic problem.
Trisomy 18 affects 1 out of every 7,500 births. Children with this syndrome have a low birth weight and a small head, mouth, and jaw. Their hands typically form clenched fists with fingers that overlap. They also might have birth defects involving the hips and feet, heart and kidney problems, and intellectual disability (also called mental retardation). Only about 5% of these children are expected to live longer than 1 year.
Trisomy 13 affects 1 out of every 15,000 to 25,000 births. Children with this condition often have cleft lip and palate, extra fingers or toes, foot abnormalities, and many different structural abnormalities of the skull and face. This condition also can cause birth defects of the ribs, heart, abdominal organs, and sex organs. Long-term survival is unlikely but possible.
In monosomy, another form of numerical error, one member of a chromosome pair is missing. So there are too few chromosomes rather than too many. A baby with a missing autosome has little chance of survival. However, a baby with a missing sex chromosome can survive in certain cases. For example, girls with Turner syndrome — who are born with just one X chromosome — can live normal, productive lives as long as they receive medical care for any health problems associated with their condition.
Deletions, Translocations, and Inversions
Sometimes it's not the number of chromosomes that's the problem, but that the chromosomes have something wrong with them, like an extra or missing part. When a part is missing, it's called a deletion (if it's visible under a microscope) and a microdeletion (if it's too tiny to be visible). Microdeletions are so small that they may involve only a few genes on a chromosome.
Some genetic disorders caused by deletions and microdeletions include Wolf-Hirschhorn syndrome (affects chromosome 4), Cri-du-chat syndrome (chromosome 5), DiGeorge syndrome (chromosome 22), and Williams syndrome (chromosome 7).
In translocations (which affect about 1 in every 400 newborns), bits of chromosomes shift from one chromosome to another. Most translocations are "balanced," which means there is no gain or loss of genetic material. But some are "unbalanced," which means there may be too much genetic material in some places and not enough in others. With inversions (which affect about 1 in every 100 newborns), small parts of the DNA code seem to be snipped out, flipped over, and reinserted. Translocations may be either inherited from a parent or happen spontaneously in a child's own chromosomes.
Both balanced translocations and inversions typically cause no malformations or developmental problems in the kids who have them. However, those with either translocations or inversions who wish to become parents may have an increased risk of miscarriage or chromosome abnormalities in their own children. Unbalanced translocations or inversions are associated with developmental and/or physical abnormalities.
Genetic problems also occur when abnormalities affect the sex chromosomes. Normally, a child will be a male if he inherits one X chromosome from his mother and one Y chromosome from his father. A child will be a female if she inherits a double dose of X (one from each parent) and no Y.
Sometimes, however, children are born with only one sex chromosome (usually a single X) or with an extra X or Y. Girls with Turner syndrome are born with only one X chromosome, whereas boys with Klinefelter syndrome are born with 1 or more extra X chromosomes ( XXY or XXXY).
Sometimes, too, a genetic problem is X-linked, meaning that it is associated with an abnormality carried on the X chromosome. Fragile X syndrome, which causes intellectual disability in boys, is one such disorder. Other diseases that are caused by abnormalities on the X chromosome include hemophilia and Duchenne muscular dystrophy.
Females may be carriers of these diseases, but because they also inherit a normal X chromosome, the effects of the gene change are minimized. Males, on the other hand, only have one X chromosome and are almost always the ones who show the full effects of the X-linked disorder.
Some genetic problems are caused by a single gene that is present but altered in some way. Such changes in genes are called mutations. When there is a mutation in a gene, the number and appearance of the chromosomes is usually still normal.
To pinpoint the defective gene, scientists use sophisticated DNA testing techniques. Genetic illnesses caused by a single problem gene include phenylketonuria (PKU), cystic fibrosis, sickle cell disease, Tay-Sachs disease, and achondroplasia (a type of dwarfism).
Although experts used to think that no more than 3% of all human diseases were caused by errors in a single gene, new research shows that this is an underestimate. Within the last few years, scientists have discovered genetic links to many different diseases that weren't originally thought of as genetic, including Parkinson's disease, Alzheimer's disease, heart disease, diabetes, and several different types of cancer. Alterations in these genes are thought to increase one's risk of developing these conditions.
Oncogenes (Cancer-Causing Genes)
Researchers have identified about 50 cancer-causing genes that greatly increase a person's odds of developing cancer. By using sophisticated tests, doctors may be able to identify who has these genetic mutations, and determine who is at risk.
For example, scientists have determined that colorectal cancer is sometimes associated with mutations in a gene called APC. They've also discovered that abnormalities in the BRCA1 and BRCA2 gene give women a 50% chance of developing breast cancer and an increased risk for ovarian tumors.
People who are known to have these gene mutations now can be carefully monitored by their doctors. If problems develop, they're more likely to get treated for cancer earlier than if they hadn't known of their risk, and this can increase their odds of survival.
New Discoveries, Better Care
Scientists have made major strides in the field of genetics over the last two decades. The mapping of the human genome and the discovery of many disease-causing genes has led to a better understanding of the human body. This has enabled doctors to provide better care to their patients and to increase the quality of life for people (and their families) living with genetic conditions.
Reviewed by: Nina Powell-Hamilton, MD
Date reviewed: April 28, 2017