Russell Silver Syndrome (RSS) is a rare disorder affecting growth in stature. Limb length discrepancy (LLD) is one of the main difficulties in RSS. Affected individuals usually also have difficulty feeding and failure to thrive, in addition to a constitutional short stature.
Many children with RSS also have a small face with distinctive facial features, such as prominent forehead, narrow chin, and small jaw. RSS is quite rare, occurring between 1 in 75,000 individuals to 1 in 100,000.
The genetic background of RSS is quite complex. Most cases of RSS are sporadic, suggesting that the disease was not inherited. The disorder has been linked to mutations in chromosome 7 and chromosome 11. One copy of each chromosome is inherited from each parent. Normally, both copies are expressed. For some genes, only one copy (from the mother or from the father) is expressed and this is regulated by a process called genomic imprinting. This is done via methylation, a process in which small methyl groups are attached to the DNA, blocking transcription, and effectively “turning off” the gene. RSS is thought to be caused by a loss of methylation in key genes involved in growth and development. This is an example of an epigenetic (rather than genetic) disorder.