Diagnostic application of kidney allograft-derived absolute cell-free DNA levels during transplant dysfunction.

Graft-derived cell-free DNA (donor-derived cell-free DNA) is an emerging marker of kidney allograft injury. Studies examining the clinical validity of this biomarker have previously used the graft fraction, or proportion of total cell-free DNA that is graft-derived. The present study evaluated the diagnostic validity of absolute measurements of graft-derived cell-free DNA, as well as calculated graft fraction, for the diagnosis of graft dysfunction. Plasma graft-derived cell-free DNA, total cell-free DNA, and graft fraction were correlated with biopsy diagnosis as well as individual Banff scores. Sixty-one samples were included in the analysis. For the diagnosis of antibody mediated rejection, the receiver-operator characteristic area under the curves of graft-derived cell-free DNA and graft fraction were 0.91 (95% CI 0.82-0.98) and 0.89 (95% CI 0.79-0.98), respectively. Both measures did not diagnose borderline or type 1A cellular mediated rejection. Graft fraction was associated with a broader range of Banff lesions, including lesions associated with cellular mediated rejection, while graft-derived cell-free DNA appeared more specific for antibody mediated rejection. Limitations of this study include a small sample size and lack of a validation cohort. The capacity for absolute quantification, and lower barriers to implementation of this methodology recommend it for further study.

Identification of Males with Cryptic Fragile X Alleles by Methylation-Specific Quantitative Melt Analysis.

BACKGROUND: FMR1 full mutations (FMs) (CGG expansion >200) in males mosaic for a normal (<45 CGG) or gray-zone (GZ) (45-54 CGG) allele can be missed with the standard 2-step fragile X syndrome (FXS) testing protocols, largely because the first-line PCR tests showing a normal or GZ allele are not reflexed to the second-line test that can detect FM. METHODS: We used methylation-specific quantitative melt analysis (MS-QMA) to determine the prevalence of cryptic FM alleles in 2 independent cohorts of male patients (994 from Chile and 2392 from Australia) referred for FXS testing from 2006 to 2013. All MS-QMA-positive cases were retested with commercial triplet primed PCR, methylation-sensitive Southern blot, and a methylation-specific EpiTYPER-based test. RESULTS: All 38 FMs detected with the standard 2-step protocol were detected with MS-QMA. However, MS-QMA identified methylation mosaicism in an additional 15% and 11% of patients in the Chilean and Australian cohorts, respectively, suggesting the presence of a cryptic FM. Of these additional patients, 57% were confirmed to carry cryptic expanded alleles in blood, buccal mucosa, or saliva samples. Further confirmation was provided by identifying premutation (CGG 55-199) alleles in mothers of probands with methylation-sensitive Southern blot. Neurocognitive assessments showed that low-level mosaicism for cryptic FM alleles was associated with cognitive impairment or autism. CONCLUSIONS: A substantial number of mosaic FM males who have cognitive impairment or autism are not diagnosed with the currently recommended 2-step testing protocol and can be identified with MS-QMA as a first-line test.

Relationships between age and epi-genotype of the FMR1 exon 1/intron 1 boundary are consistent with non-random X-chromosome inactivation in FM individuals, with the selection for the unmethylated state being most significant between birth and puberty.

Methylation of the fragile X-related epigenetic element 2 (FREE2) located on the exon 1/intron 1 boundary of the FMR1 gene is related to FMRP expression and cognitive impairment in full mutation (FM; CGG>200) individuals. We examined the relationship between age, the size of the FMR1 CGG expansion and the methylation output ratio (MOR) at 12 CpG sites proximal to the exon 1/intron 1 boundary using FREE2 MALDI-TOF MS. The patient cohort included 119 males and 368 females, i.e. 121 healthy controls (CGG<40), 176 premutation (CGG 55-170) and 190 FM (CGG 213-2000). For all CpG units examined, FM males showed a significantly elevated MOR compared with that in hypermethylated FM females. In FM males the MOR for most CpG units significantly positively correlated with both age and CGG size (P< 0.05). In FM females the skewing towards the unmethylated state was significant for half of the units between birth and puberty (P < 0.05). The methylation status of intron 1 CpG10-12 that was most significantly related to cognitive impairment in our earlier study, did not change significantly with age in FM females. These results challenge the concept of fragile X syndrome (FXS)-related methylation being static over time, and suggest that due to the preference for the unmethylated state in FM females, X-inactivation at this locus is not random. The findings also highlight that the prognostic value of FXS methylation testing is not uniform between all CpG sites, and thus may need to be evaluated on a site-by-site basis.

Detection of skewed X-chromosome inactivation in Fragile X syndrome and X chromosome aneuploidy using quantitative melt analysis.

Methylation of the fragile X mental retardation 1 (FMR1) exon 1/intron 1 boundary positioned fragile X related epigenetic element 2 (FREE2), reveals skewed X-chromosome inactivation (XCI) in fragile X syndrome full mutation (FM: CGG > 200) females. XCI skewing has been also linked to abnormal X-linked gene expression with the broader clinical impact for sex chromosome aneuploidies (SCAs). In this study, 10 FREE2 CpG sites were targeted using methylation specific quantitative melt analysis (MS-QMA), including 3 sites that could not be analysed with previously used EpiTYPER system. The method was applied for detection of skewed XCI in FM females and in different types of SCA. We tested venous blood and saliva DNA collected from 107 controls (CGG < 40), and 148 FM and 90 SCA individuals. MS-QMA identified: (i) most SCAs if combined with a Y chromosome test; (ii) locus-specific XCI skewing towards the hypomethylated state in FM females; and (iii) skewed XCI towards the hypermethylated state in SCA with 3 or more X chromosomes, and in 5% of the 47,XXY individuals. MS-QMA output also showed significant correlation with the EpiTYPER reference method in FM males and females (P < 0.0001) and SCAs (P < 0.05). In conclusion, we demonstrate use of MS-QMA to quantify skewed XCI in two applications with diagnostic utility.

Early detection of fragile X syndrome: applications of a novel approach for improved quantitative methylation analysis in venous blood and newborn blood spots.

BACKGROUND: Standard fragile X syndrome (FXS) diagnostic tests that target methylation of the fragile X mental retardation 1 (FMR1) CpG island 5' of the CGG expansion can be used to predict severity of the disease in males from birth, but not in females. METHODS: We describe methylation specific-quantitative melt analysis (MS-QMA) that targets 10 CpG sites, with 9 within FMR1 intron 1, to screen for FXS from birth in both sexes. The novel method combines the qualitative strengths of high-resolution melt and the high-throughput, quantitative real-time PCR standard curve to provide accurate quantification of DNA methylation in a single assay. Its performance was assessed in 312 control (CGG <40), 143 premutation (PM) (CGG 56-170), 197 full mutation (FM) (CGG 200-2000), and 33 CGG size and methylation mosaic samples. RESULTS: In male and female newborn blood spots, MS-QMA differentiated FM from control alleles, with sensitivity, specificity, and positive and negative predictive values between 92% and 100%. In venous blood of FM females between 6 and 35 years of age, MS-QMA correlated most strongly with verbal IQ impairment (P = 0.002). In the larger cohort of males and females, MS-QMA correlated with reference methods Southern blot and MALDI-TOF mass spectrometry (P < 0.05), but was not significantly correlated with age. Unmethylated alleles in high-functioning FM and PM males determined by both reference methods were also unmethylated by MS-QMA. CONCLUSIONS: MS-QMA has an immediate application in FXS diagnostics, with a potential use of its quantitative methylation output for prognosis in both sexes.

Use of copy number deletion polymorphisms to assess DNA chimerism.

BACKGROUND: We describe a novel approach that harnesses the ubiquity of copy number deletion polymorphisms in human genomes to definitively detect and quantify chimeric DNA in clinical samples. Unlike other molecular approaches to chimerism analysis, the copy number deletion (CND) method targets genomic loci (>50 base pairs in length) that are wholly absent from wild-type (i.e., self) background DNA sequences in a sex-independent manner. METHODS: Bespoke quantitative PCR (qPCR) CND assays were developed and validated using a series of DNA standards and chimeric plasma DNA samples collected from 2 allogeneic kidney transplant recipients and 12 pregnant women. Assay performance and informativeness were assessed using appropriate statistical methods. RESULTS: The CND qPCR assays showed high sensitivity, precision, and reliability for linear quantification of DNA chimerism down to 16 genomic equivalents (i.e., 106 pg). Fetal fraction (%) in 12 singleton male pregnancies was calculated using the CND qPCR approach, which showed closer agreement with single-nucleotide polymorphism-based massively parallel sequencing than the SRY (sex determining region Y) (Y chromosome) qPCR assay. The latter consistently underestimated the fetal fraction relative to the other methods. We also were able to measure biological changes in plasma nonself DNA concentrations in 2 renal transplant recipients. CONCLUSIONS: The CND qPCR technique is suitable for measurement of chimerism for monitoring of rejection in allogeneic organ transplantation and quantification of the cell-free fetal DNA fraction in maternal plasma samples used for noninvasive prenatal genetic testing.

Characterization of core clinical phenotypes associated with recurrent proximal 15q25.2 microdeletions.

A recurrent proximal microdeletion at 15q25.2 with an approximate 1.5 megabase smallest region of overlap has recently been reported in seven patients and is proposed to be associated with congenital diaphragmatic hernia (CDH), mild to moderate cognitive deficit, and/or features consistent with Diamond-Blackfan anemia. We report on four further patients and define the core phenotypic features of individuals with this microdeletion to include mild to moderate developmental delay or intellectual disability, postnatal short stature, anemia, and cryptorchidism in males. CDH and structural organ malformations appear to be less frequent associations, as is venous thrombosis. There is no consistent facial dysmorphism. Features novel to our patient group include dextrocardia, obstructive sleep apnea, and cleft lip.

Fragile X-related element 2 methylation analysis may provide a suitable option for inclusion of fragile X syndrome and/or sex chromosome aneuploidy into newborn screening: a technical validation study.

PURPOSE: We show that a novel fragile X-related epigenetic element 2 FMR1 methylation test can be used along with a test for sex-determining region Y (SRY) to provide the option of combined fragile X syndrome and sex chromosome aneuploidy newborn screening. METHODS: Fragile X-related epigenetic element 2, SRY, and FMR1 CGG repeat analyses were performed on blood and saliva DNA, and in adult and newborn blood spots. The cohort consisted of 159 controls (CGG <40), 187 premutation (CGG 56-170), and 242 full-mutation (CGG ~200-2,000) males and females, 106 sex chromosome aneuploidy individuals, and 151 cytogenetically normal controls. RESULTS: At the 0.435 threshold, fragile X-related epigenetic element 2 analysis in males was robust on both blood DNA and newborn blood spots, with specificity and sensitivity of ~100% for full-mutation genotype. In females, the specificity was 99%, whereas half of full-mutation females were above the 0.435 threshold in both blood DNA and newborn blood spots. Furthermore, at this threshold, the test could not differentiate individuals with Klinefelter syndrome from female controls without using the SRY marker. When combined with SRY analysis, the test was consistent with most results for sex chromosome aneuploidies from karyotyping. CONCLUSION: Setting specific thresholds for fragile X-related epigenetic element 2 analysis and including the SRY marker provides the option to either include or exclude detection of sex chromosome aneuploidies as part of fragile X syndrome newborn screening.

Application of a new molecular technique for the genetic evaluation of products of conception.

OBJECTIVES: Karyotyping is a well-established method of investigating the genetic content of product of conceptions (POCs). Because of the high rate of culture failure and maternal cell contamination, failed results or 46,XX findings are often obtained. Different molecular approaches that are not culture dependent have been proposed to circumvent these limits. On the basis of the robust experience previously obtained with bacterial artificial chromosomes (BACs)-on-Beads™ (BoBs™), we evaluated the same technology that we had used for the analysis of prenatal samples on POCs. METHOD: KaryoLite™ BoBs™ includes 91 beads, each of which is conjugated with a composite of multiple neighboring BACs according to the hg19 assembly. It quantifies proximal and terminal regions of each chromosome arm. The study included 376 samples. RESULTS: The failure rate was 2%, and reproducibility >99%; false-positive and false-negative rates were <1% for non-mosaic aneuploidies and imbalances effecting all three BACs in a contig. Detection rate for partial terminal imbalances was 65.5%. The mosaic detection threshold was 50%, and the success rate in macerated samples was 87.8%. The aneuploidy detection rate in samples with cell growth failure was 27.8%, and maternal cell contamination was suspected in 23.1% of 46,XX cultured cells. CONCLUSION: KaryoLite™ BoBs™ as a 'first-tier' test in combination with other approaches showed beneficial, cost-effective and clearly enhanced POC testing.

Molecular and clinical characterization of 25 individuals with exonic deletions of NRXN1 and comprehensive review of the literature.

This study aimed to elucidate the observed variable phenotypic expressivity associated with NRXN1 (Neurexin 1) haploinsufficiency by analyses of the largest cohort of patients with NRXN1 exonic deletions described to date and by comprehensively reviewing all comparable copy number variants in all disease cohorts that have been published in the peer reviewed literature (30 separate papers in all). Assessment of the clinical details in 25 previously undescribed individuals with NRXN1 exonic deletions demonstrated recurrent phenotypic features consisting of moderate to severe intellectual disability (91%), severe language delay (81%), autism spectrum disorder (65%), seizures (43%), and hypotonia (38%). These showed considerable overlap with previously reported NRXN1-deletion associated phenotypes in terms of both spectrum and frequency. However, we did not find evidence for an association between deletions involving the ß-isoform of neurexin-1 and increased head size, as was recently published in four cases with a deletion involving the C-terminus of NRXN1. We identified additional rare copy number variants in 20% of cases. This study supports a pathogenic role for heterozygous exonic deletions of NRXN1 in neurodevelopmental disorders. The additional rare copy number variants identified may act as possible phenotypic modifiers as suggested in a recent digenic model of neurodevelopmental disorders.

Fragile X mental retardation 1 (FMR1) intron 1 methylation in blood predicts verbal cognitive impairment in female carriers of expanded FMR1 alleles: evidence from a pilot study.

BACKGROUND: Cognitive status in females with mutations in the FMR1 (fragile X mental retardation 1) gene is highly variable. A biomarker would be of value for predicting which individuals were liable to develop cognitive impairment and could benefit from early intervention. A detailed analysis of CpG sites bridging exon 1 and intron 1 of FMR1, known as fragile X-related epigenetic element 2 (FREE2), suggests that a simple blood test could identify these individuals. METHODS: Study participants included 74 control females (<40 CGG repeats), 62 premutation (PM) females (55-200 CGG repeats), and 18 full-mutation (FM) females assessed with Wechsler intelligence quotient (IQ) tests. We used MALDI-TOF mass spectrometry to determine the methylation status of FREE2 CpG sites that best identified low-functioning (IQ <70) FM females (>200 CGG repeats), compared the results with those for Southern blot FMR1 activation ratios, and related these assessments to the level of production of the FMR1 protein product in blood. RESULTS: A methylation analysis of intron 1 CpG sites 10-12 showed the highest diagnostic sensitivity (100%) and specificity (98%) of all the molecular measures tested for detecting females with a standardized verbal IQ of <70 among the study participants. In the group consisting of only FM females, methylation of these sites was significantly correlated with full-scale IQ, verbal IQ, and performance IQ. Several verbal subtest scores showed strong correlation with the methylation of these sites (P = 1.2 × 10(-5)) after adjustment for multiple measures. CONCLUSIONS: The data suggest that hypermethylation of the FMR1 intron 1 sites in blood is predictive of cognitive impairment in FM females, with implications for improved fragile X syndrome diagnostics in young children and screening of the newborn population.

Extending the scope of diagnostic chromosome analysis: detection of single gene defects using high-resolution SNP microarrays.

Microarray analysis has provided significant advances in the diagnosis of conditions resulting from submicroscopic chromosome abnormalities. It has been recommended that array testing should be a "first tier" test in the evaluation of individuals with intellectual disability, developmental delay, congenital anomalies, and autism. The availability of arrays with increasingly high probe coverage and resolution has increased the detection of decreasingly small copy number changes (CNCs) down to the intragenic or even exon level. Importantly, arrays that genotype SNPs also detect extended regions of homozygosity. We describe 14 examples of single gene disorders caused by intragenic changes from a consecutive set of 6,500 tests using high-resolution SNP microarrays. These cases illustrate the increased scope of cytogenetic testing beyond dominant chromosome rearrangements that typically contain many genes. Nine of the cases confirmed the clinical diagnosis, that is, followed a "phenotype to genotype" approach. Five were diagnosed by the laboratory analysis in the absence of a specific clinical diagnosis, that is, followed a "genotype to phenotype" approach. Two were clinically significant, incidental findings. The importance of astute clinical assessment and laboratory-clinician consultation is emphasized to optimize the value of microarrays in the diagnosis of disorders caused by single gene copy number and sequence mutations.

Evidence for the toxicity of bidirectional transcripts and mitochondrial dysfunction in blood associated with small CGG expansions in the FMR1 gene in patients with parkinsonism.

PURPOSE: Our previous results showed that both gray zone and lower end premutation range (40-85 repeats) fragile X mental retardation 1 (FMR1) alleles were more common among males with parkinsonism than in the general population. This study aimed to determine whether these alleles have a significant role in the manifestations and pathogenesis of parkinsonian disorders. METHODS: Detailed clinical assessment and genetic testing were performed in 14 male carriers of premutation and gray zone FMR1 alleles and in 24 noncarriers identified in a sample of males with parkinsonism. RESULTS: The premutation + gray zone carriers presented with more severe symptoms than disease controls matched for age, diagnosis, disease duration, and treatment. The Parkinson disease (Unified Parkinson's Disease Rating Scale) motor score and the measures of cognitive decline (Mini-Mental State Examination and/or Addenbrooke's Cognitive Examination Final Revised Version A scores) were significantly correlated with the size of the CGG repeat and the (elevated) levels of antisense FMR1 and Cytochrome C1 mRNAs in blood leukocytes. In addition, the carriers showed a significant depletion of the nicotinamide adenine dinucleotide, reduced dehydrogenase subunit 1 mitochondrial gene in whole blood. CONCLUSION: Small CGG expansion FMR1 alleles (gray zone and lower end premutation) play a significant role in the development of the parkinsonian phenotype, possibly through the cytotoxic effect of elevated sense and/or antisense FMR1 transcripts involving mitochondrial dysfunction and leading to progressive neurodegeneration.

Phenotypic variability of distal 22q11.2 copy number abnormalities.

The availability of microarray technology has led to the recent recognition of copy number abnormalities of distal chromosome 22q11.2 that are distinct from the better-characterized deletions and duplications of the proximal region. This report describes five unrelated individuals with copy number abnormalities affecting distal chromosome 22q11.2. We report on novel phenotypic features including diaphragmatic hernia and uterine didelphys associated with the distal microdeletion syndrome; and frontomedial polymicrogyria and callosal agenesis associated with the distal microduplication syndrome. We describe the third distal chromosome 22q11.2 microdeletion patient with Goldenhar syndrome. Patients with distal chromosome 22q11.2 copy number abnormalities exhibit inter- and intra-familial phenotypic variability, and challenge our ability to draw meaningful genotype-phenotype correlations.

Further molecular and clinical delineation of co-locating 17p13.3 microdeletions and microduplications that show distinctive phenotypes.

BACKGROUND: Chromosome 17p13.3 contains extensive repetitive sequences and is a recognised region of genomic instability. Haploinsufficiency of PAFAH1B1 (encoding LIS1) causes either isolated lissencephaly sequence or Miller-Dieker syndrome, depending on the size of the deletion. More recently, both microdeletions and microduplications mapping to the Miller-Dieker syndrome telomeric critical region have been identified and associated with distinct but overlapping phenotypes. METHODS: Genome-wide microarray screening was performed on 7678 patients referred with unexplained learning difficulties and/or autism, with or without other congenital abnormalities. Eight and five unrelated individuals, respectively, were identified with microdeletions and microduplications in 17p13.3. RESULTS: Comparisons with six previously reported microdeletion cases identified a 258 kb critical region, encompassing six genes including CRK (encoding Crk) and YWHAE (encoding 14-3-3epsilon). Clinical features included growth retardation, facial dysmorphism and developmental delay. Notably, one individual with only subtle facial features and an interstitial deletion involving CRK but not YWHAE suggested that a genomic region spanning 109 kb, encompassing two genes (TUSC5 and YWHAE), is responsible for the main facial dysmorphism phenotype. Only the microduplication phenotype included autism. The microduplication minimal region of overlap for the new and previously reported cases spans 72 kb encompassing a single gene, YWHAE. These genomic rearrangements were not associated with low-copy repeats and are probably due to diverse molecular mechanisms. CONCLUSIONS: The authors further characterise the 17p13.3 microdeletion and microduplication phenotypic spectrum and describe a smaller critical genomic region allowing identification of candidate genes for the distinctive facial dysmorphism (microdeletions) and autism (microduplications) manifestations.

Development of a multiplex ligation-dependent probe amplification assay for diagnosis and estimation of the frequency of spinocerebellar ataxia type 15.

BACKGROUND: Spinocerebellar ataxia type 15 (SCA15) is a slowly progressive neurodegenerative disorder characterized by cerebellar ataxia. Mutation of the ITPR1 gene (inositol 1,4,5-triphosphate receptor, type 1) has been identified recently as the underlying cause, and in most cases the molecular defect is a multiexon deletion. To date, 5 different SCA15 families have been identified with ITPR1 gene deletion. METHODS: We have designed a synthetic, dual-color multiplex ligation-dependent probe amplification (MLPA) assay that measures copy number with high precision in selected exons across the entire length of ITPR1 and the proximal region of the neighboring gene, SUMF1 (sulfatase modifying factor 1). We screened 189 idiopathic ataxic patients with this MLPA assay. RESULTS: We identified ITPR1 deletion of exons 1-10 in the previously reported AUS1 family (4 members) and deletion of exons 1-38 in a new family (2 members). In addition to the multiexon deletions, apparent single-exon deletions identified in 2 other patients were subsequently shown to be due to single-nucleotide changes at the ligation sites. CONCLUSIONS: The frequency of ITPR1 deletions is 2.7% in known familial cases. This finding suggests that SCA15 is one of the "less common" SCAs. Although the deletions in the 5 families identified worldwide thus far have been of differing sizes, all share deletion of exons 1-10. This region may be important, both in terms of the underlying pathogenetic mechanism and as a pragmatic target for an accurate, robust, and cost-effective diagnostic analysis.

Improved methodology for assessment of mRNA levels in blood of patients with FMR1 related disorders.

BACKGROUND: Elevated levels of FMR1 mRNA in blood have been implicated in RNA toxicity associated with a number of clinical conditions. Due to the extensive inter-sample variation in the time lapse between the blood collection and RNA extraction in clinical practice, the resulting variation in mRNA quality significantly confounds mRNA analysis by real-time PCR. METHODS: Here, we developed an improved method to normalize for mRNA degradation in a sample set with large variation in rRNA quality, without sample omission. Initially, RNA samples were artificially degraded, and analyzed using capillary electrophoresis and real-time PCR standard curve method, with the aim of defining the best predictors of total RNA and mRNA degradation. RESULTS: We found that: (i) the 28S:18S ratio and RNA quality indicator (RQI) were good predictors of severe total RNA degradation, however, the greatest changes in the quantity of different mRNAs (FMR1, DNMT1, GUS, B2M and GAPDH) occurred during the early to moderate stages of degradation; (ii) chromatographic features for the 18S, 28S and the inter-peak region were the most reliable predictors of total RNA degradation, however their use for target gene normalization was inferior to internal control genes, of which GUS was the most appropriate. Using GUS for normalization, we examined in the whole blood the relationship between the FMR1 mRNA and CGG expansion in a non-coding portion of this gene, in a sample set (n = 30) with the large variation in rRNA quality. By combining FMR1 3' and 5' mRNA analyses the confounding impact of mRNA degradation on the correlation between FMR1 expression and CGG size was minimized, and the biological significance increased from p = 0.046 for the 5' FMR1 assay, to p = 0.018 for the combined FMR1 3' and 5' mRNA analysis. CONCLUSION: Our observations demonstrate that, through the use of an appropriate internal control and the direct analysis of multiple sites of target mRNA, samples that do not conform to the conventional rRNA criteria can still be utilized to obtain biologically/clinically relevant data. Although, this strategy clearly has application for improved assessment of FMR1 mRNA toxicity in blood, it may also have more general implications for gene expression studies in fresh and archival tissues.

Incomplete silencing of full mutation alleles in males with fragile X syndrome is associated with autistic features.

Background: Fragile X syndrome (FXS) is a common monogenic cause of intellectual disability with autism features. While it is caused by loss of the FMR1 product (FMRP), mosaicism for active and inactive FMR1 alleles, including alleles termed premutation (PM: 55-199 CGGs), is not uncommon. Importantly, both PM and active full mutation (FM: ≥ 200 CGGs) alleles often express elevated levels of mRNA that are thought to be toxic. This study determined if complete FMR1 mRNA silencing from FM alleles and/or levels of FMR1 mRNA (if present) in blood are associated with intellectual functioning and autism features in FXS. Methods: The study cohort included 98 participants (70.4% male) with FXS (FM-only and PM/FM mosaic) aged 1-43 years. A control group of 14 females were used to establish control FMR1 mRNA reference range. Intellectual functioning and autism features were assessed using the Mullen Scales of Early Learning or an age-appropriate Wechsler Scale and the Autism Diagnostic Observation Schedule-2nd Edition (ADOS-2), respectively. FMR1 mRNA was analysed in venous blood collected at the time of assessments, using the real-time PCR relative standard curve method. Results: Females with FXS had significantly higher levels of FMR1 mRNA (p < 0.001) than males. FMR1 mRNA levels were positively associated with age (p < 0.001), but not with intellectual functioning and autistic features in females. FM-only males (aged < 19 years) expressing FM FMR1 mRNA had significantly higher ADOS calibrated severity scores compared to FM-only males with completely silenced FMR1 (p = 0.011). However, there were no significant differences between these subgroups on intellectual functioning. In contrast, decreased levels of FMR1 mRNA were associated with decreased intellectual functioning in FXS males (p = 0.029), but not autism features, when combined with the PM/FM mosaic group. Conclusion: Incomplete silencing of toxic FM RNA may be associated with autistic features, but not intellectual functioning in FXS males. While decreased levels of mRNA may be more predictive of intellectual functioning than autism features. If confirmed in future studies, these findings may have implications for patient stratification, outcome measure development, and design of clinical and pre-clinical trials in FXS.

ß-glucuronidase use as a single internal control gene may confound analysis in FMR1 mRNA toxicity studies.

Relationships between Fragile X Mental Retardation 1 (FMR1) mRNA levels in blood and intragenic FMR1 CGG triplet expansions support the pathogenic role of RNA gain of function toxicity in premutation (PM: 55-199 CGGs) related disorders. Real-time PCR (RT-PCR) studies reporting these findings normalised FMR1 mRNA level to a single internal control gene called ß-glucuronidase (GUS). This study evaluated FMR1 mRNA-CGG correlations in 33 PM and 33 age- and IQ-matched control females using three normalisation strategies in peripheral blood mononuclear cells (PBMCs): (i) GUS as a single internal control; (ii) the mean of GUS, Eukaryotic Translation Initiation Factor 4A2 (EIF4A2) and succinate dehydrogenase complex flavoprotein subunit A (SDHA); and (iii) the mean of EIF4A2 and SDHA (with no contribution from GUS). GUS mRNA levels normalised to the mean of EIF4A2 and SDHA mRNA levels and EIF4A2/SDHA ratio were also evaluated. FMR1mRNA level normalised to the mean of EIF4A2 and SDHA mRNA levels, with no contribution from GUS, showed the most significant correlation with CGG size and the greatest difference between PM and control groups (p = 10-11). Only 15% of FMR1 mRNA PM results exceeded the maximum control value when normalised to GUS, compared with over 42% when normalised to the mean of EIF4A2 and SDHA mRNA levels. Neither GUS mRNA level normalised to the mean RNA levels of EIF4A2 and SDHA, nor to the EIF4A2/SDHA ratio were correlated with CGG size. However, greater variability in GUS mRNA levels were observed for both PM and control females across the full range of CGG repeat as compared to the EIF4A2/SDHA ratio. In conclusion, normalisation with multiple control genes, excluding GUS, can improve assessment of the biological significance of FMR1 mRNA-CGG size relationships.