A study into newborn screening for fragile X syndrome (FXS) demonstrates that testing for mutations in the gene FMR1 can be done on a large scale, according to a paper published in Genome Medicine which shows that the number of carrier babies who carry the form of the gene known as the "premutation" is higher than previously estimated.

Fragile X syndrome (FXS) is the most common cause of inherited intellectual disability and autism, or autism spectrum disorder, and is caused by mutations in the gene FMR1.

The mutation which causes FXS is not actually in the gene but is due to the addition of extra CGG repeats in the promoter region that controls whether the gene is switched on or off.

The full mutation of more than 200 CGG repeats prevents proper functioning of the gene and causes FXS, while premutation (55 to 200 repeats) means that the baby has a higher chance of having a child with FXS, and has an increased risk child and adult-onset disorders such as neurological complications. The impact of so called 'grey zone allele' (45 to 54 repeats) on health is currently not as clear, and is the focus of ongoing research. However, the team also found that the Caucasian group had a higher prevalence of grey zone alleles than the Hispanic and African American groups.

Three large hospitals in the U.S.A. participated in this study, testing more than 14,000 newborns, including children of different ethnic backgrounds. While only one child was identified with the full mutation, the team, led by Dr. Flora Tassone from U.C. Davis found that the prevalence of the premutation was higher than previously suggested, particularly for males (one in 209 females and one in 430 males). 

Tassone explains, "Our study shows that screening newborns for FXS can be done, but we will also identify carrier and grey zone babies as well as those with a full mutation. Before newborn screening for fragile X mutations is expanded nationally, we need to better understand the impact that identification of the premutation and grey zone allele has on families and systems will need to be in place to address the counseling and educational needs that inevitably will arise."