Mosaic trisomy 14

Mosaic trisomy 14 is a rare chromosomal disorder in which there are 3 copies (trisomy) of chromosome 14 in some cells of the body, while other cells have the usual two copies. The extent and severity of features in affected individuals can vary. Signs and symptoms that have been most commonly reported include intrauterine growth restriction; failure to to thrive; developmental delay; intellectual disability; distinctive facial characteristics; structural malformations of the heart; and other physical abnormalities.^[1][2] This condition is most often caused by an error in cell division in the egg or sperm cell before conception, or in fetal cells after fertilization. Treatment is directed toward the specific signs and symptoms in each individual.^[1]

The effects of mosaic trisomy 14 can vary considerably among affected individuals. Some children with mosaic trisomy 14 grow into healthy, if small, children. Others may have continued difficulty thriving.^[2] Those that have a low percentage of affected cells may have fewer and/or less severe symptoms than those with a high percentage of affected cells.^[1] Some of the more commonly reported characteristics of the condition include:^[1][2]

• intrauterine growth restriction
• feeding difficulties
• failure to thrive
• some degree of developmental delay or intellectual disability
• slightly asymmetrical growth
• abnormal skin pigmentation
• structural defect(s) of the heart such as tetralogy of Fallot
• minor genital abnormalities in boys such as undescended testes
• distinctive facial characteristics such as a prominent forehead; widely spaced eyes; a broad nasal bridge; low-set, malformed ears; a small lower jaw; a large mouth and thick lips; eye abnormalities; or abnormality of the roof of the mouth (palate)

Skeletal abnormalities have also been reported and include dislocation of the hips; overlapping of certain fingers or toes; and/or other features.^[1]

Individuals with mosaic trisomy 14 have a duplication of chromosome 14 material in some of their cells, while other cells have a normal chromosomal makeup. The additional chromosomal material is responsible for the features that are characteristic of the condition.^[1]

Most cases of mosaic trisomy 14 appear to result from random errors in the separation of chromosomes (nondisjunction) -- either during the division of the egg or sperm in one of the parents, or during cell division after fertilization. There have been some reports in which it may have occurred due to other phenomenon, such as uniparental disomy or the formation of an isochromosome. Uniparental disomy is when an affected individual inherits both copies of a chromosomal pair from one parent, rather than one copy from each parent. An isochromosome is an abnormal chromosome with identical arms on each side of the centromere.^[1]

Unique has a leaflet on their Web site that contains additional descriptions and illustrations of how mosaic trisomy 14 may occur. Click here to view the leaflet.

Treatment for signs and symptoms of mosaic trisomy 14 focuses on the specific features present in each individual. Infants with congenital heart defects may need surgery or other therapies to alleviate symptoms and correct heart malformations. Respiratory infections should be treated aggressively and early. Some infants and children with the condition may need surgical repair of certain craniofacial, genital, or other abnormalities. Early intervention may be important in ensuring that children with the reach their potential. Special services that may be beneficial include special education, physical therapy, and/or other medical, social, and/or vocational services.^[1]