FMR1 premutation in children with autism spectrum disorders: Should additional diagnostic tests be performed?

To the Editor The premutation of the Fragile X Mental Retardation 1 gene (FMR1) is an expansion of the (CGG)n repeat in the 50 untranslated region, within the range of 55–200 trinucleotides. Expanded repeats with more than 200 trinucleotides result in FMR1 methylation and transcriptional silencing, characterizing the full causative mutations of the Fragile X syndrome (FXS), the most prevalent inherited cause of intellectual disability. The frequency of FMR1 premutation carriers in the population was estimated in about 1:855 among males and 1:291 among females in a meta-analysis including 88,673 females and 45,253 males (Hunter et al., 2014). Two adult-onset disorders were well documented as being casually associated with FMR1 premutation: fragile X primary ovarian insufficiency (FXPOI), in 20% of female carriers, and fragile X-associated tremor/ataxia syndrome (FXTAS) affecting both females (16%) and males (40%) aged ≥50 (reviewed by Hagerman & Hagerman, 2016; Mila et al., 2018). Studies have suggested that FMR1 premutation is also a risk factor for neurodevelopmental disorders (NDD) such as autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), intellectual disability (ID) (Aziz et al., 2003; Bailey et al., 2008; Clifford et al., 2007; Farzin et al., 2006), and broad autism spectrum symptoms (Schneider et al., 2016). However, some of these associations are still controversial (Hunter et al., 2008; Mila et al., 2018). Therefore, the high frequency of the FMR1 premutation in the population critically requires a better understanding of its clinical significance as a risk factor in neurodevelopmental disorders, such as ASD, and will contribute both to define the genetic cause of NDD and improve genetic counseling. In order to clarify the clinical relevance of the FMR1 premutation in NDD, we screened a cohort of 1055 Brazilian ASD male patients for the FMR1 full mutation and premutation. All the affected individuals were screened at the Centro de Estudos do Genoma Humano e Células Tronco (CEGH-CEL) IB-USP, by following previous standardized criteria (Griesi-Oliveira et al., 2012), which included anamnesis, pregnancy history, developmental history, weight, height and head circumference measurements, and pedigree analyses. All probands included in this study were referred to our center with a formal ASD diagnosis established by a neurologist or a psychiatrist at the Instituto de Psiquiatria, Hospital da Cínicas – Universidade de S~ao Paulo, based on the Diagnostic and Statistical Manual of Mental Disorders, 4th or 5th edition (DSM IV or 5) (Griesi-Oliveira et al., 2020; Moreira et al., 2014; Satterstrom et al., 2020). CARS, ADI-R, and Vineland scales were applied whenever possible in our Center by a psychologist. Patients who were exposed to teratogenic agents or prenatal infections were excluded from the study. About 13% of our patients had a syndromic form of autism following the criteria of Miles et al. (2005). Participants' ages ranged from 1.5 to 38.6 years (M = 7.6, SD = 5.4). These individuals are part of a larger cohort of autistic patients who were genetically investigated from 2001 to 2017. Only males were selected for FMR1 expansion testing, which was the first-tier test. The FMR1 full mutation and premutation were screened by PCR (according to Haddad et al., 1996). Positive cases Received: 24 May 2021 Revised: 15 November 2021 Accepted: 5 December 2021