What is autosomal recessive?
An autosomal recessive disorder means two copies of a gene mutation must be present at a particular locus for the disease or trait to appear. Autosomal genes are those genes that are present on one of the first 22 pairs of non-sex chromosomes (also known as autosomes). Recessive inheritance means both the genes in a pair must be malformed in order to produce the disease. In the example below, two parents who are unaffected each carry a gene mutation for an autosomal recessive disorder. They are therefore “carriers” of the disease but do not manifest the disease. They have one affected child and three unaffected child among which two are also “carriers” of the disease.
Inheritance of Autosomal recessive trait
What is the risk to family members?
The parents of an affected individual are heterozygote carriers of the mutated gene. As illustrated in the diagram above, each sibling of the affected individual has a 50% chance of being a carrier, a 25% chance of being affected and a 25% chance of being neither affected nor a carrier. The risk of the unaffected sibling being a carrier is 2/3. An affected individual’s offspring will be a heterozygote carrier; however the carrier frequency for RTS is unknown since the disorder is very rare.
Clinical trial on calcium absorption in patients with RTS
Patients with Rothmund-Thomson syndrome have an increased risk of developing osteosarcoma, which is a malignant tumor of the bone. A study investigating 33 RTS patients showed that 11 of them were diagnosed with osteosarcoma and contained at least one of the 19 mutations in their RECQL4 gene. They suggested that there may be at least two forms of this disorder: Type I RTS and Type II RTS. Initially this disorder was described as a characteristic poikiloderma with no osteosarcoma and this is now believed to be described as the Type I form of the disorder. Type II RTS is described as the form that is manifested by poikiloderma as well as increased risk of osteosarcoma and detrimental mutations in the RECQL4 gene (Wang et al., 2003b).
Osteosarcoma is the most common form of bone cancer in youth. It tends to occur in the bones of the shin, thigh and upper arm. The most common region of growth of the tumor is in the area of the bone with the fastest growth rate. Visit the following link to learn about an ongoing clinical trial on the absorption of calcium in patients with RTS:
Mechanism of Helicases
The RecQL4 belongs to the family of helicases, which are proteins necessary for living organisms. These motor proteins are vital for many cellular processes such as DNA replication, transcription, translation, DNA repair etc, where unwinding of the nucleic acid strands are involved. The following clip shows the basic structure of the family of helicases and their mechanism of action.
- Gene Review: Rothmund-Thomson Syndrome
- Wang LL, Gannavarapu A, Kozinetz CA, Levy ML, Lewis RA, Chintagumpala MM, Ruiz-Maldanado R, Contreras-Ruiz J, Cunniff C, Erickson RP, Lev D, Rogers M, Zackai EH, Plon SE. Association between osteosarcoma and deleterious mutations in the RECQL4 gene in Rothmund-Thomson syndrome.J Natl Cancer Inst. 2003 May 7;95(9):669-74.