What Is the Inheritance for Dwarfism?

Dwarfism is a general term describing disorders resulting in small stature. There are several disorders that can cause dwarfism; not all of them are genetically inherited. The majority of people with dwarfism lead normal lives with minimal, if any, health problems.

Types

• Not all forms of dwarfism are caused by genetic disorders. Dwarfism can result from insufficient growth-hormone production, a low-functioning pituitary gland or other deficiencies in the endocrine system. One of the most common forms of dwarfism is achondroplasia: This is an inheritable disorder that affects the formation of cartilage in the long bones of the body. About 70 percent of dwarfism is achondroplastic. A person with achondroplastic dwarfism has a normal-sized head and trunk but disproportionately sized limbs.

Inheritance

• There are 46 chromosomes in the human genome. Chromosomes are arranged in 23 pairs; each pair contains duplicate genes or alleles that code for a specific trait, like eye color or hair texture. The first 22 pairs of chromosomes are called autosomes. The last pair contains the sex chromosomes---X or Y---and determines the sex of the individual. Achondroplastic dwarfism is inherited in an autosomal-dominant pattern; in this case, "dominance" is just a term that describes a pattern of inheritance in which one gene can suppress the expression of the other in the allelic pair. This means that one achondroplastic dwarfism gene is enough to cause the disorder.

Effects

• Eighty percent of people with achondroplastic dwarfism come from parents of average height. Their disorder is the result of a new genetic mutation in the gene called the fibroblast growth factor receptor 3 (FGFR3). The FGFR3 gene is responsible for regulating the growth of long bones like the femur and humerus.

  The other 20 percent of affected individuals inherit the FGFR3 gene from one or both parents. A child with two affected parents has a 50 percent chance of inheriting both genes, a 25 percent chance of inheriting one gene and a 25 percent chance of not inheriting the mutated gene at all. If both FGFR3 genes are inherited by the child, serious bone-development problems may result. These problems are usually so severe that the child is stillborn or dies shortly after birth due to respiratory failure.

Health Problems

• If only one dwarfism gene is inherited, there is a great likelihood that the child will lead a healthy, normal life. However, some people affected with achondroplastic dwarfism may still have health problems. Problems like back pain, swayback, bowed legs, obesity, recurrent ear infections, apnea and other respiratory problems are most common.

Prevention

• There's no way to prevent achondroplasia since the mutation can occur spontaneously in children of average-sized parents. Genetic counseling is currently the only means used to address the disorder. Parents affected with achondroplastic dwarfism, as well as parents whose baby has developed the mutation, are offered genetic counseling to help make decisions about family planning and learn about caring for children with genetic disorders.