Russell Silver syndrome (RSS) H19 Methylation Panel
Russell-Silver syndrome is a growth disorder characterized by slow growth before and after birth. Babies with this condition have a low birth weight and often fail to grow and gain weight at the expected rate (failure to thrive). Head growth is normal, however, so the head may appear unusually large compared to the rest of the body. Affected children are thin and have poor appetites, and some develop recurrent episodes of low blood sugar (hypoglycemia) as a result of feeding difficulties. Adults with Russell-Silver syndrome are short; the average height for affected men is about 151 centimeters (4 feet, 11 inches) and the average height for affected women is about 140 centimeters (4 feet, 7 inches).
Many children with Russell-Silver syndrome have a small, triangular face with distinctive facial features including a prominent forehead, a narrow chin, a small jaw, and downturned corners of the mouth. Other features of this disorder can include an unusual curving of the fifth finger (clinodactyly), asymmetric or uneven growth of some parts of the body, and digestive system abnormalities. Russell-Silver syndrome is also associated with an increased risk of delayed development, speech and language problems, and learning disabilities.
The genetic causes of Russell-Silver syndrome are complex. The disorder often results from the abnormal regulation of certain genes that control growth. Research has focused on genes located in particular regions of chromosome 7 and chromosome 11.
People normally inherit one copy of each chromosome from their mother and one copy from their father. For most genes, both copies are expressed, or "turned on," in cells. For some genes, however, only the copy inherited from a person's father (the paternal copy) is expressed. For other genes, only the copy inherited from a person's mother (the maternal copy) is expressed. These parent-specific differences in gene expression are caused by a phenomenon called genomic imprinting. Both chromosome 7 and chromosome 11 contain groups of genes that normally undergo genomic imprinting; some of these genes are active only on the maternal copy of the chromosome, while others are active only on the paternal copy. Abnormalities involving these genes appear to be responsible for many cases of Russell-Silver syndrome.
Researchers suspect that 30 to 50 percent of all cases of Russell-Silver syndrome result from changes in a process called methylation on the short (p) arm of chromosome 11 at position 15 (11p15). Methylation is a chemical reaction that attaches small molecules called methyl groups to certain segments of DNA. In genes that undergo genomic imprinting, methylation is one way that a gene's parent of origin is marked during the formation of egg and sperm cells. Russell-Silver syndrome has been associated with changes in methylation involving the H19 gene, which is located at chromosome region 11p15. These genes are thought to be involved in directing normal growth. A loss of methylation disrupts the regulation of these genes, which leads to slow growth and the other characteristic features of this disorder. Abnormalities involving genes on chromosome 7 can also cause Russell-Silver syndrome. In 7 to 10 percent of cases, people inherit both copies of chromosome 7 from their mother instead of one copy from each parent which results in uniparental disomy (UPD). In about 40 percent of people with Russell-Silver syndrome, the cause of the condition is unknown.
Methodology: Methylation-specific (MS-MLPA) Methylation studies of H19
Purpose: Confirmation of Clinical Diagnosis
Test Requisition: Molecular Requisition
CPT Code: 81401 Cost: $400.00 (Oklahoma Medicaid requires preauthorization for this test)
Turn-around-time: 21 days
1. American College of Medical Genetics Statement on diagnostic testing for uniparental disomy. Available online. 2001. Accessed 3-17-16.