Introduction
Chromosomes are components of the cell nucleus that house DNA-based structures that carry the genetic code. Humans have 46 pairs of chromosomes, including a pair of sex chromosomes (that is, XX in females and XY in males) and 22 pairs of autosomes. Numerous genes with specific instructions can be found on each chromosome. During conception, one copy of each chromosome is inherited from each parent. Genetic abnormalities caused by chromosome number or structure abnormalities can result in birth defects, growth delays, or intellectual disabilities.
Schinzel first reported on Mosaic trisomy 22 in 1981, and approximately 20 cases of live-born children with this condition have been documented since then. It is thought that children with Mosaic trisomy 22 who have minor physical characteristics and normal development are not identified frequently enough.
What Is Mosaic Trisomy 22?
Mosaic trisomy 22 is a rare genetic disorder that results in three copies of chromosome 22 in some body cells. Mosaic refers to cells with an extra copy of chromosome 22; others have only two copies. It is also known as mosaic trisomy chromosome 22 syndrome or trisomy 22 mosaicism. Females are more likely to be affected by this condition, and the severity and range of associated symptoms can vary greatly. Mosaic trisomy 22 is characterized by prenatal and postnatal growth delays or failure, asymmetrical body development (hemidystrophy), and congenital heart defects. While some people with this condition have abnormal cognitive development, others have reported normal development.
What Causes Mosaic Trisomy 22?
Mosaic trisomy 22 is a condition in which specific cell populations in the body have an extra copy of chromosome 22 (trisomy). This condition can be because of an error that happens during the division of the reproductive cells in one of the parents (or mitotic nondisjunction) or during the cell division that results from fertilization (fetal mitosis). The disorder may also be associated with uniparental disomy, a condition in which affected people inherit copies of a chromosomal pair from one parent rather than a single copy from each parent. An additional chromosome 22 in certain cell groups causes the condition's typical symptoms and physical features.
What Are the Risk Factors for Mosaic Trisomy 22?
Mosaic trisomy 22 syndrome is an uncommon chromosomal disorder that can affect people of any age or gender, though it is more common in women. Its exact prevalence is unknown, with only around 20 cases reported yet. Symptoms may appear during or shortly after birth, but many cases with mild symptoms may go undiagnosed. There are currently no identified risk factors for the syndrome, including lifestyle, environmental, or prenatal factors. It is essential to emphasize that having a risk factor does not guarantee the onset of the condition, and the absence of a risk factor does not guarantee protection from the syndrome. Seeking advice from a healthcare provider to discuss the consequences of potential risk factors is advisable.
What Are the Symptoms of Mosaic Trisomy 22?
Depending on the proportion and distribution of cells carrying an extra copy of chromosome 22, the severity and symptoms of mosaic trisomy 22 may vary. Despite this, the disorder is frequently associated with asymmetric body development, growth and developmental delays, and congenital heart diseases. Most Mosaic trisomy 22 patients have intrauterine growth restriction and postnatal growth failure. Even though developmental delays are common, up to 40 of patients who have been reported have normal development. The percentage of trisomic cells has no relationship with the severity of the developmental delay.
Hemidystrophy, or asymmetric body development, is common, with hearing loss in one ear being common in affected individuals. Patients with Mosaic trisomy 22 frequently have congenital heart defects, the most common of which are atrial and ventricular septal defects. The size and severity of these defects determine how they are treated. Mosaic trisomy 22 patients frequently have dysmorphic characteristics like preauricular pits, epicanthic folds, renal malformations, flat nasal bridge, abnormal palmar flexion creases, mesobrachydactyly or clinodactyly, and linear pigmentary changes along Blaschko lines. Female patients with ovarian dysgenesis or streak ovaries, which can cause infertility and delayed or unsuccessful development of secondary sexual characteristics, are uncommon but possible conditions.
How Is Mosaic Trisomy 22 Diagnosed?
Mosaic trisomy 22 syndromes can manifest in various ways, and some people with mild manifestations may go undiagnosed. Because of the condition's rarity, healthcare providers should consider it a possible diagnosis and may require specialized tests to confirm it. Mosaic trisomy 22 can be detected during pregnancy using specialized tests such as ultrasound and amniocentesis. Ultrasound uses sound waves to generate images of the fetus, and if the results are unusual, invasive procedures like amniocentesis might be required. Mosaic trisomy 22 can be detected through chromosomal analysis of amniotic fluid or chorionic tissue, but confirmation can require fetal blood sampling or skin biopsy. Normal ultrasound results, however, do not guarantee normal development. Mosaic trisomy 22 can be diagnosed through clinical evaluation and chromosomal testing after birth. Normal blood karyotyping does not rule out mosaicism because trisomic cells may only be found in specific tissues. Specialized tests may be performed to detect associated abnormalities.
How Is Mosaic Trisomy 22 Treated?
Mosaic trisomy 22 syndrome is a genetic disorder for which no cure exists. It is treated based on the specific symptoms observed in each individual, and it may necessitate the collaboration of multiple healthcare professionals, including pediatricians, cardiologists, surgeons, ophthalmologists, and others. Infants with mosaic trisomy 22 may require surgery to repair congenital heart defects and craniofacial and other impairments associated with the condition in some cases. The extent of the anatomical abnormalities and their accompanying symptoms will determine the kind of surgical procedures needed.
Prosthetic devices such as specialized hearing aids may benefit patients with hearing loss. Children with mosaic trisomy 22 require early intervention to reach their full potential. Specialized services such as physical therapy, speech therapy, special education, and medical, social, and vocational services may be beneficial. Individuals with the condition and their families should seek genetic counseling to better understand the condition and its implications.
Conclusion
Mosaic trisomy 22 syndrome is a rare genetic disorder characterized by various symptoms affecting multiple body systems. The severity of the signs and symptoms, as well as the body systems affected, can all have a significant impact on prognosis, but with adequate medical intervention and support from a multidisciplinary team of healthcare professionals, many people with Mosaic trisomy 22 syndromes can live fulfilling lives. Regular medical screening and symptom management are critical in ensuring the best possible outcomes for those affected by this condition. To manage the condition and optimize long-term outcomes, affected individuals and their families must seek appropriate medical care and support services.
