The condition of being abnormally short or small, dwarfism has numerous causes. Some of these are hereditary, but all concern hormone disturbances, bone or deficiency diseases, and/or organ dysfunction. Two ailments--achondroplasiaand pituitary dwarfism--are the most common causes of dwarfism.

Achondroplasia is a condition in which the development of cartilage, and therefore bone, is disturbed. The disorder appears in approximately one in every10,000 births. The bones (especially those in the limbs) do not grow as longas they should, and simultaneously become abnormally thick. The bones in thetrunk of the body and the skull are mostly unaffected, although the skull opening through which the spinal cord passes (foramen magnum) is often narrowerthan normal, and the opening through which the spinal cord runs (spinal canal) becomes abnormally small as it goes down the length of the spine.

Achondroplasia is caused by a genetic defect. It is a dominant trait, so anybody with the genetic defect will display all the symptoms of the disorder. Aparent with it has a 50% chance of passing achondroplasia on to his or her child. Although the disorder can also be passed on to that child's offspring, the majority of cases occur due to a new mutation (change) in a gene. Interestingly, the defect caused by achondroplasia is one of only a few that are known to become more frequent as the father ages. (Many genetic defects are linked to the mother's increasing age.)

People with achondroplasia have abnormally short arms and legs, although because their torsos and heads are usually of normal size, their heads appear tobe too big. The bridge of the nose often has a scooped-out appearance due toa characteristic trait called "saddle nose," while the lower back is overly curved, producing "sway back." The face of a dwarf often displays an excessively prominent forehead and a relatively undeveloped upper-jaw area. Because the foramen magnum and spinal canal are too narrow, nerve damage may occur if these openings become compressed. The narrowed foramen magnum may also disruptthe normal flow of fluid between the brain and the spinal cord, resulting inhydrocephalus (the accumulation of too much fluid in the brain). Children with achondroplasia have a very high risk of serious and repeated middle-ear infections, which can result in hearing loss if left untreated. The disorder does not affect either mental capacity or reproductive ability.

As of the late 1990s, there is no treatment to reverse the defect present inachondroplasia, and the only form of prevention is through genetic counseling, which could help parents assess their risk of having a child with achondroplasia. Treatment primarily addresses some of the complications of the disorder, including problems due to nerve compression, hydrocephalus, bowed legs, and abnormal curves in the spine. However, most dwarves enjoy good health and can have a normal lifespan.

The other main cause of dwarfism, pituitary dwarfism, is a rare condition ofgrowth retardation characterized by patients who are very short in stature but have normal body proportions (unlike the achondroplasic dwarves). Thus, they are sometimes referred to as "proportionate dwarves." Some children with this condition go through delayed but normal puberty and have normal reproductive capabilities, while others never become sexually mature.

In most cases where children fail to attain a normal height, it is not possible to identify a specific pituitary or genetic disorder. Children born with cleft palates or who suffer serious head trauma, severe environmental deprivation, tumors of the pituitary gland, or brain infections or bleeding are all more likely to have pituitary dwarfism. Endocrinologists (doctors who specialize in the functioning of hormones) have the most experience in diagnosing andtreating this disorder.

Pituitary dwarfism is caused by a dysfunction of the pituitary gland, a pea-sized mass of tissue at the base of the brain that has two sections (anteriorand posterior). Each of these secretes hormones essential for regulating thebody's processes, including growth. Pituitary dwarfism occurs only in children. (Low hormonal output from the pituitary in adults produces different disorders.)

There are two categories of pituitary dwarfism. The first is panhypopituitarism, which is caused by a deficit of all the anterior pituitary hormones. These patients, who account for about two-thirds of pituitary dwarfism cases, have generalized slow growth and do not go through puberty. They also have manyother medical disorders, including problems in metabolic regulation and waterbalance and failure to develop secondary sexual characteristics.

The second category involves an isolated deficiency of growth hormone (GH), which accounts for about one-third of cases. These patients do mature sexuallyand may reproduce. When there is a deficit of only GH, children grow very slowly and reach sexual maturity long after their peers. These children are below the third percentile in height, and their rate of growth is less than 1.5in (4 cm) per year. GH deficiency is hereditary in about 10% of pituitary dwarfism cases. Pituitary dwarfism with sexual maturity has been linked to an inherited recessive gene.

Untreated pituitary dwarfs who lack multiple pituitary hormones often die. The success of multiple hormone replacement therapy depends on which hormones are absent, the severity of the deficit, and the age at which replacement begins. Treatment becomes a complex balancing act in which combinations of GH andthe other missing hormones are replaced. As the child grows, the dosages ofreplacement hormones are frequently changed to reflect his or her changing metabolic state.

Treatment for GH-only pituitary dwarfism focuses on replacement GH therapy for children with documented GH deficiency. (This therapy must be started early, while the long bones can still grow. For this reason, replacement GH therapy is ineffective in adults.) The long-term effectiveness of GH replacement therapy is still being studied. Research in this area continues, and gene replacement therapy may be a possible solution for some forms of pituitary dwarfism.

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