Expanding the phenotype of mosaic trisomy 20

Abstract

Mosaic trisomy 20 is one of the more common cytogenetic abnormalities found on amniocentesis or chorionic villus sampling. Studies have shown that outcome is normal in 90-93% of prenatally diagnosed cases. There are however, reports in the literature of children with mosaic trisomy 20 described as having an assortment of dysmorphic features and varying levels of developmental delay. Unfortunately, the literature has not defined a specific phenotype for this entity. Here we report on three patients with mosaic trisomy 20, two of whom were identified prenatally. Over a number of years of follow-up it has become apparent that there are some striking similarities among the three. Comparison between our patients and the literature cases indicates a more consistent phenotype than has previously been suggested. Recurring features include; spinal abnormalities (including spinal stenosis, vertebral fusion, and kyphosis), hypotonia, lifelong constipation, sloped shoulders, and significant learning disabilities despite normal intelligence. These findings may be overlooked on routine history and physical exam or assumed to be standard pediatric problems. It is not our intention to suggest that there is a distinctive face for this entity but to suggest that a subtle phenotype does exist. We have attempted to identify a set of findings for which any child diagnosed with mosaic trisomy 20 should be assessed or followed even in the presence of an apparently normal physical exam at birth.

Mosaic trisomy 20: Considerations for genetic counseling

“…Finally we agree with Willis et al [2008] in the opportunity to long term follow up mosaic trisomy 20 patients with special attention to spinal evaluation even if in the majority of reported cases these anomalies manifested without serious complications.…”

“…Thus, in absence of severe structural anomalies and even though a mild phenotype cannot be excluded as suggested by Willis et al [2008], it is important to reassure the parents about the unlikelihood of severe mental retardation and dysmorphic appearance, findings that often are the most important components in the decision of voluntary termination the pregnancy in the absence of structural anomalies on prenatal ultrasonography. Finally we agree with Willis et al [2008] in the opportunity to long term follow up mosaic trisomy 20 patients with special attention to spinal evaluation even if in the majority of reported cases these anomalies manifested without serious complications.…”

“…Moreover, firm conclusions for genetic counseling are not evident. Recently, Willis et al [2008] reported three patients with mosaic trisomy 20, two of whom were identified prenatally and suggest that with long term follow up a subtle phenotype does exist and includes spinal abnormalities (spinal stenosis, vertebral fusion, and kyphosis), hypotonia, lifelong constipation, sloped shoulders, and significant learning disabilities despite normal intelligence. Some of these findings may be overlooked on routine history and physical exam or assumed to be standard pediatric problems.…”

Constitutional and Acquired Autosomal Aneuploidy

“…As a result of this phenotypic overlap, the term “general chromosomal mosaic syndrome” has been coined [ 35 ]. However, for a subset of these conditions, specific syndromic patterns have emerged (summarized in Table 2 [ 4,16,21,23-25,33-75 ]), thereby facilitating the recognition of the chromosomal basis for these individual's health/developmental problems. The provision of genetic counseling following a prenatal diagnosis of autosomal mosaicism can be especially challenging.…”

Uniparental disomy and the phenotype of mosaic trisomy 20: a new case and review of the literature

“…Thus it continues to be a challenge with regards to providing counseling for families (Bianca et al 2008;Willis et al 2008). A variety of features have been reported in children with this abnormality (Hsu et al 1991).…”