Children With FMR1 Premutation Experience Difficulties in Sensory Processing, Study Reveals

Children with the FMR1 premutation experience difficulties in processing sensory information, similar to those experienced by children with fragile x syndrome, a study shows.

The study, “Sensory Difficulties in Children With an FMR1 Premutation,” was published in the journal Frontiers in Genetics.

Fragile x syndrome (FXS) is caused by a mutation, known as a trinucleotide repeat expansion, in the FMR1 gene. Patients with FXS have more than 200 repeats of the trinucleotide sequence CGG in the FMR1 gene, which leads to a deficiency in the production of the fragile X mental retardation protein (FMRP).

A lack of FMRP causes intellectual disability and a number of other conditions such as anxiety, attention problems, autism, and associated medical problems — including seizures and otitis media (inflammatory diseases of the middle ear).

One of the hallmark symptoms in FXS patients are sensory processing problems, which begin early in life and continue to be a challenge as patients get older.

When compared with typically developing children, FXS children show higher rates of tactile (sense of touch) and taste/smell sensitivity, as well as auditory filtering.

Individuals with 55 to 200 CGG repeats in the FMR1 gene, less than those necessary for FXS to manifest, have what is known as the FMR1 premutation. This can lead to a full FXS mutation in future generations.

Individuals with the FMR1 premutation can develop two known associated conditions — fragile X-associated tremor/ataxia syndrome (FXTAS) and fragile X-associated premature ovarian insufficiency (FXPOI).

FXTAS is characterized by progressive tremor and ataxia (clumsy and uncoordinated movements), executive function and memory deficits, among other symptoms. FXPOI affects women and is characterized by reduced function of the ovaries, expressed as irregular menstrual cycles, early menopause, and infertility.

A growing body of evidence suggests that individuals with the FMR1 premutation may have a similar — although tempered — phenotype to individuals with the full mutation. As such, increased dysfunction in sensory processing may also be present in children with the FMR1 premutation.

Researchers compared the differences in sensory difficulties in children with the FMR1 premutation with children with FXS , and typically developing children.

The team conducted an online survey of 176 parents of children (younger than 18 years, with a mean age of 13 years, and 70% male) with either FXS or FMR1 premutation. Most respondents were mothers who were Caucasian (86%), had a 4-year college or graduate degree (68%), and were married (92%).

Participants completed the BBC Sensory Scales — a 50-item scale comprising 8 subscales that evaluate auditory processing, visual processing, tactile processing, and eating and feeding behaviors.

Across all subscales, children with the FMR1 premutation displayed more sensory challenges compared with typically developing children.

For six out of the eight subscales, children with the full mutation had the lowest scores — indicating the most sensory challenges — followed closely by children with the FMR1 premutation, who displayed more sensory challenges than typically developing children.

Children with the FMR1 premutation also scored lower in about one-third (32%) of the items compared with children with the full mutation. Digestive problems and tactile sensitivity were the highest sensory challenges for children with the FMR1 premutation.

“These data provide further evidence that some children with an FMR1 premutation experience sensory difficulties that are similar to children with FXS but different than typically developing children,” the researchers concluded.