Newborn Screening for “Bubble Boy Disease”: Interview
On the 1st of January, the state of Wisconsin made a major step in the field of newborn screening. The collaboration of Wisconsin State Laboratory of Hygiene, Children’s Hospital of Wisconsin and the Jeffrey Modell Foundation resulted in screening newborns for Severe Combined Immune Deficiency (SCID). According to the Wikipedia article this is:
…a genetic disorder in which both B and T cells of the adaptive immune system are crippled, due to a defect in one of several possible genes. SCID is a severe form of heritable immunodeficiency. It is also known as the “bubble boy” disease because its victims are extremely vulnerable to infectious diseases.
I’ve already presented The Jeffrey Modell Foundation (headquarters in New York) to you in June. Now, to know more about this medical breakthrough, Dr. Jack Routes from the Children’s Hospital of Wisconsin answered some of my questions:
- How common is the so-called “Bubble Boy Disease” in the US and in your hospital?
There is no good data on the actual incidence of the disease in the US. It is estimated that at least 1:100,000 newborns have SCID. Our newborn screening program will better ascertain the true incidence of SCID in Wisconsin.
- Is a blood sample taken from a newborn enough for the screening process?
All newborn screening tests are performed from blood spotted on a newborn screening card—the newborn gets a heel stick and blood is put on a special filter paper on the newborn screening card. A small punch is taken from the filter paper and the SCID screening test is performed.
- Please tell us some more details of the screening of SCID! How sensitive and predictive is the test?
Please see the article ( J Allergy Clin Immunol. 2005 Feb;115(2):391-8.) for a discussion of the assay. These are the only published data to date. The assay is a real time, quantitative PCR that measures the number of T cell receptor excision circles (TRECs) in the punch from a newborn screening card. TRECs are a surrogate marker for functional, naïve T cells, which will be reduced in most, but not all causes of SCID. Our group has improved the TREC assay (false positive rate is <0.01%) over the results reported in the JACI paper. There is no data on sensitivity and positive predictive value of the test—-this issue will be addressed by the WI SCID screening program.
- Do you plan to add new medical conditions to the newborn screening program?
Wisconsin constantly evaluates other genetic diseases to add for newborn screening. The WI Newborn Screening Umbrella Committee addresses this issue and I am not a member of this committee and do not know if other tests are being considered in the near future.
I’m thankful to Dr. John Routes for the answers. This is a great example of how to construct a successful newborn screening program. Just to show you the difference, in Hungary, they screen newborns for only 4 (while they screen for 47 in Wisconsin) genetic conditions (galactosaemia, congenital hypothyreosis, biotinidase deficiency and phenylketonuria)