Advances in overgrowth syndromes: clinical classification to molecular delineation in Sotos syndrome and Beckwith-Wiedemann syndrome

PURPOSE OF REVIEW

The clinical importance of overgrowth syndromes in the pediatric patient population has been increasingly recognized during the past decade, but clinical overlap among overgrowth syndromes often makes diagnostic categorization difficult. Advances in the molecular delineation of overgrowth syndromes in recent years have furthered our knowledge of the phenotypic spectrum of this group of conditions. This review focuses on developments in our understanding of the molecular mechanisms and phenotype-genotype correlations in the two most common overgrowth syndromes, Beckwith-Wiedemann syndrome and Sotos syndrome. The implications of these findings with respect to clinical diagnosis, medical management, and genetic counseling are discussed.

RECENT FINDINGS

Recent reports have redefined the cardinal clinical features of Sotos syndrome, and the identification of two distinct types of molecular alterations in patients with this syndrome has enabled assessment of phenotype-genotype correlations. Recent studies in patients with Beckwith-Wiedemann syndrome have further expanded our understanding of the causative molecular mechanisms of this condition and provide evidence for specific genotype-phenotype correlations, most notably with respect to tumor risk.

SUMMARY

Recognition of childhood overgrowth and investigation of diagnostic causes is important in anticipating appropriate medical management and facilitating the provision of genetic counseling. New developments in our understanding of the molecular basis and phenotypic expression of overgrowth syndromes provide additional tools in this often challenging process.

Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is a clinically heterogeneous overgrowth syndrome associated with an increased risk for embryonal tumor development. BWS provides an ideal model system to study epigenetic mechanisms. This condition is caused by a variety of genetic or epigenetic alterations within two domains of imprinted growth regulatory genes on human chromosome 11p15. Molecular studies of BWS have provided important data with respect to epigenotype/genotype-phenotype correlations; for example, alterations of Domain 1 are associated with the highest risk for tumor development, specifically Wilms' tumor. Further, the elucidation of the molecular basis for monozygotic twinning in BWS defined a critical period for imprint maintenance during pre-implantation embryonic development. In the future, such molecular studies in BWS will permit enhanced medical management and targeted genetic counseling.

Early recognition of infant malignancy: the five most common infant cancers

The incidence of cancer in children is rising in the U.S. Although cancer in the first year of life is relatively rare, understanding the early signs and symptoms of and the historical factors associated with most common infant cancers is essential for providing optimal care to these infants and their families. Neonatal nurses and nurse practitioners play a pivotal role in early recognition and detection of infant malignancy. This article reviews the incidence of and historical factors associated with infant cancers and discusses clinical presentations and available diagnostic images as well as screening tools for the five most common types of infant malignancy.

Recognition and management of childhood cancer syndromes: a systems approach

Recognition of congenital anomalies that predispose to childhood cancer allows for the institution of a cancer surveillance program, identification of relatives with increased cancer risk, and recurrence risk counseling. In this article, a systems approach to the diagnosis of 21 childhood cancer syndromes is set forth in the format of the pediatric physical examination. In the second part of this article, guidelines are presented for genetic testing, cancer screening, and genetic counseling for the 21 cancer syndromes.

Nephrogenic rest associated with a mesoblastic nephroma--what does it tell us?

A 3-year-old girl presented with a tumor in the right kidney that was found to be a mesoblastic nephroma on histological examination. In addition, between the tumor and renal parenchyma there was a large perilobar sclerosing nephrogenic rest--a finding that has rarely been reported previously in non-Wilms renal tumors of childhood. We believe this supports the theory that both mesoblastic nephroma and Wilms tumor arise from the developing kidney but the key difference is the time point at which induction of neoplasm occurs.