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Spectrum: Autism Research News

Clinical research: Newborn screening can diagnose fragile X

by  /  15 March 2013
THIS ARTICLE IS MORE THAN FIVE YEARS OLD

This article is more than five years old. Autism research — and science in general — is constantly evolving, so older articles may contain information or theories that have been reevaluated since their original publication date.

Heel prick: Clinicians use dried blood spots collected from newborns to screen for genetic disorders.

A mild form of fragile X syndrome that can lead to the full syndrome in one generation is more common than previously thought, according to a large study published 21 December in Genome Medicine1.

FMR1, the fragile X syndrome gene, harbors a series of repeats (typically about 30 copies) of three DNA nucleotides. Errors during DNA replication can multiply these repeats. Having in excess of 200 repeats leads to a DNA modification that shuts off expression of FMR1 and results in fragile X syndrome.

Individuals who have between 55 and 200 repeats are said to have a ‘premutation,’ which may expand to the full mutation in the following generation.

Because the FMR1 gene is on the X chromosome, boys, who have only copy of the gene, are more severely affected by the mutations than are girls. The premutation may lead to symptoms such as infertility in some women and fragile X tremor ataxia, or late-onset tremors, in some men.

Doctors screen blood spots from newborn infants for a number of genetic disorders. Fragile X syndrome is typically not on that list, but advances in treatments and screening procedures suggest that it should be, the researchers say.

In the new study, they screened 14,207 newborn samples for full-blown fragile X syndrome and the premutation. The screening identified one infant boy with the full mutation, 50 infants with the premutation and 170 infants who have between 45 and 54 repeats. The last category is considered a ‘gray zone’ that may lead to characteristics of the premutation.

The researchers estimate that the prevalence for the premutation is 1 in 209 for girls and 1 in 430 for boys. A Canadian study published in 2002 found half the rate for boys2

The premutation doesn’t always lead to symptoms, which typically appear in adulthood. Researchers should better understand its effects before recommending universal screening for fragile X syndrome, they say.

References:

1: Tassone F. et al. Genome Med. 4, 100 (2012) PubMed

2: Dombrowski C. et al. Hum. Mol. Genet. 11, 371-378 (2002) PubMed