Models of KPTN-related disorder implicate mTOR signalling in cognitive and overgrowth phenotypes.

KPTN-related disorder is an autosomal recessive disorder associated with germline variants in KPTN (previously known as kaptin), a component of the mTOR regulatory complex KICSTOR. To gain further insights into the pathogenesis of KPTN-related disorder, we analysed mouse knockout and human stem cell KPTN loss-of-function models. Kptn -/- mice display many of the key KPTN-related disorder phenotypes, including brain overgrowth, behavioural abnormalities, and cognitive deficits. By assessment of affected individuals, we have identified widespread cognitive deficits (n = 6) and postnatal onset of brain overgrowth (n = 19). By analysing head size data from their parents (n = 24), we have identified a previously unrecognized KPTN dosage-sensitivity, resulting in increased head circumference in heterozygous carriers of pathogenic KPTN variants. Molecular and structural analysis of Kptn-/- mice revealed pathological changes, including differences in brain size, shape and cell numbers primarily due to abnormal postnatal brain development. Both the mouse and differentiated induced pluripotent stem cell models of the disorder display transcriptional and biochemical evidence for altered mTOR pathway signalling, supporting the role of KPTN in regulating mTORC1. By treatment in our KPTN mouse model, we found that the increased mTOR signalling downstream of KPTN is rapamycin sensitive, highlighting possible therapeutic avenues with currently available mTOR inhibitors. These findings place KPTN-related disorder in the broader group of mTORC1-related disorders affecting brain structure, cognitive function and network integrity.

Large intragenic deletion of CDC73 (exons 4-10) in a three-generation hyperparathyroidism-jaw tumor (HPT-JT) syndrome family.

BACKGROUND: Inactivating mutations of CDC73 cause Hyperparathyroidism-Jaw Tumour syndrome (HPT-JT), Familial Isolated Hyperparathyroidism (FIHP) and sporadic parathyroid carcinoma. We conducted CDC73 mutation analysis in an HPT-JT family and confirm carrier status of the proband's daughter. METHODS: The proband had primary hyperparathyroidism (parathyroid carcinoma) and uterine leiomyomata. Her father and daughter had hyperparathyroidism (parathyroid adenoma) but no other manifestations of HPT-JT. CDC73 mutation analysis (sequencing of all 17 exons) and whole-genome copy number variation (CNV) analysis was done on leukocyte DNA of the three affecteds as well as the proband's unaffected sister. RESULTS: A novel deletion of exons 4 to 10 of CDC73 was detected by CNV analysis in the three affecteds. A novel insertion in the 5'UTR (c.-4_-11insG) that co-segregated with the deletion was identified. By in vitro assay the 5'UTR insertion was shown to significantly impair the expression of the parafibromin protein. Screening for the mutated CDC73 confirmed carrier status in the proband's daughter and the biochemistry and ultrasonography led to pre-emptive surgery and resolution of the hyperparathyroidism. CONCLUSIONS: A novel gross deletion mutation in CDC73 was identified in a three-generation HPT-JT family emphasizing the importance of including screening for large deletions in the molecular diagnostic protocol.

Triple therapy with pyridoxine, arginine supplementation and dietary lysine restriction in pyridoxine-dependent epilepsy: Neurodevelopmental outcome.

Pyridoxine-dependent epilepsy (PDE) is an epileptic encephalopathy characterized by response to pharmacologic doses of pyridoxine. PDE is caused by deficiency of α-aminoadipic semialdehyde dehydrogenase resulting in impaired lysine degradation and subsequent accumulation of α-aminoadipic semialdehyde. Despite adequate seizure control with pyridoxine monotherapy, 75% of individuals with PDE have significant developmental delay and intellectual disability. We describe a new combined therapeutic approach to reduce putative toxic metabolites from impaired lysine metabolism. This approach utilizes pyridoxine, a lysine-restricted diet to limit the substrate that leads to neurotoxic metabolite accumulation and L-arginine to compete for brain lysine influx and liver mitochondrial import. We report the developmental and biochemical outcome of six subjects who were treated with this triple therapy. Triple therapy reduced CSF, plasma, and urine biomarkers associated with neurotoxicity in PDE. The addition of arginine supplementation to children already treated with dietary lysine restriction and pyridoxine further reduced toxic metabolites, and in some subjects appeared to improve neurodevelopmental outcome. Dietary lysine restriction was associated with improved seizure control in one subject, and the addition of arginine supplementation increased the objective motor outcome scale in two twin siblings, illustrating the contribution of each component of this treatment combination. Optimal results were noted in the individual treated with triple therapy early in the course of the disease. Residual disease symptoms could be related to early injury suggested by initial MR imaging prior to initiation of treatment or from severe epilepsy prior to diagnosis. This observational study reports the use of triple therapy, which combines three effective components in this rare condition, and suggests that early diagnosis and treatment with this new triple therapy may ameliorate the cognitive impairment in PDE.

Spread of X inactivation on chromosome 15 is associated with a more severe phenotype in a girl with an unbalanced t(X; 15) translocation.

We report on a baby girl with multiple congenital abnormalities, including cleft palate, intrauterine growth restriction, and double outlet right ventricle (DORV) with ventricular septal defect. She had an unbalanced chromosome translocation t (X;15) resulting in monosomy 15pter → p10 and trisomy Xq13.1 → q28. All three copies of Xq encompass the XIST gene. It is known that X chromosome inactivation could spread to the autosome part of an unbalanced translocation involving chromosome X and an autosome. To confirm the spread of X chromosome inactivation on chromosome 15, we evaluate the methylation change by the HumanMethylation450 BeadChip, a whole genome DNA methylation micorarray that includes 15,259 probes spanning 717 genes on chromosome 15. Results showed there was gain in DNA methylation of more than 20% in 586 CpG sites spanning the long arm of chromosome 15. We further examined the hypermethylated CpG sites located in CpG-island promoter, because genes subjected to X chromosome inactivation will have an increase in DNA methylation level in this region. A total of 75 sites representing 24 genes were hypermethylated. Nearly all of these probes are located in region proximal to the breakpoint, from 15q11.2 to 15q21.3 (35Mb) suggesting that X inactivation was spread to the proximal region of 15q. Gain of DNA methylation, especially in the CpG-island promoter, can result in functional inactivation of genes, and therefore could potentially worsen the phenotype of our patient.

In brief: BRCA1 and BRCA2.

The discovery of the first major breast cancer susceptibility gene, BRCA1, occurred almost 20 years ago. BRCA1, together with BRCA2 remain the most important discoveries in human cancer genetics. Identification of highly penetrant mutations in these two tumour suppressor genes has had broad implications for women at risk and their families, for health professionals caring for these persons and for basic researchers. The BRCA proteins have many critical functions, the most notable of which, from a clinical perspective, is repair of double-strand DNA breaks.

Inherited mutations in breast cancer genes--risk and response.

Germ-line mutations in BRCA1 and BRCA2 confer a high risk of developing breast cancer. They account, however, for only 40% of strongly familial breast cancer cases. Intensive genome-wide searches for other highly-penetrant BRCA genes that, individually account for a sizeable fraction of the remaining heritability has not identified any plausible candidates. The "missing heritability" is thought to be due to cumulative effects of susceptibility alleles associated with low to moderate penetrance, in accordance with a polygenic model of inheritance. In addition, a large number of individually very rare, highly penetrant variants could account for part of the gap. Meanwhile, an understanding of the function of BRCA1 and BRCA2 in the DNA damage response pathway has lead to the identification of a number of breast cancer susceptibility genes including PALB2, CHEK2, ATM and BRIP1, all of which interact directly or indirectly with BRCA1 or BRCA2. Knowledge of how BRCA1 and BRCA2 maintain genomic integrity has also led the development of novel targeted therapies. Here we summarize the recent advances made in the understanding of the functions of these two genes, as well as the risks and responses associated with mutations in these and other breast cancer susceptibility genes.

Functional Repair Assay for the Diagnosis of Constitutional Mismatch Repair Deficiency From Non-Neoplastic Tissue.

PURPOSE: Constitutional mismatch repair deficiency (CMMRD) is a highly penetrant cancer predisposition syndrome caused by biallelic mutations in mismatch repair (MMR) genes. As several cancer syndromes are clinically similar, accurate diagnosis is critical to cancer screening and treatment. As genetic diagnosis is confounded by 15 or more pseudogenes and variants of uncertain significance, a robust diagnostic assay is urgently needed. We sought to determine whether an assay that directly measures MMR activity could accurately diagnose CMMRD. PATIENTS AND METHODS: In vitro MMR activity was quantified using a 3'-nicked G-T mismatched DNA substrate, which requires MSH2-MSH6 and MLH1-PMS2 for repair. We quantified MMR activity from 20 Epstein-Barr virus-transformed lymphoblastoid cell lines from patients with confirmed CMMRD. We also tested 20 lymphoblastoid cell lines from patients who were suspected for CMMRD. We also characterized MMR activity from patients with neurofibromatosis type 1, Li-Fraumeni syndrome, polymerase proofreading-associated cancer syndrome, and Lynch syndrome. RESULTS: All CMMRD cell lines had low MMR activity (n = 20; mean, 4.14 ± 1.56%) relative to controls (n = 6; mean, 44.00 ± 8.65%; P < .001). Repair was restored by complementation with the missing protein, which confirmed MMR deficiency. All cases of patients with suspected CMMRD were accurately diagnosed. Individuals with Lynch syndrome (n = 28), neurofibromatosis type 1 (n = 5), Li-Fraumeni syndrome (n = 5), and polymerase proofreading-associated cancer syndrome (n = 3) had MMR activity that was comparable to controls. To accelerate testing, we measured MMR activity directly from fresh lymphocytes, which yielded results in 8 days. CONCLUSION: On the basis of the current data set, the in vitro G-T repair assay was able to diagnose CMMRD with 100% specificity and sensitivity. Rapid diagnosis before surgery in non-neoplastic tissues could speed proper therapeutic management.

BAFopathies' DNA methylation epi-signatures demonstrate diagnostic utility and functional continuum of Coffin-Siris and Nicolaides-Baraitser syndromes.

Coffin-Siris and Nicolaides-Baraitser syndromes (CSS and NCBRS) are Mendelian disorders caused by mutations in subunits of the BAF chromatin remodeling complex. We report overlapping peripheral blood DNA methylation epi-signatures in individuals with various subtypes of CSS (ARID1B, SMARCB1, and SMARCA4) and NCBRS (SMARCA2). We demonstrate that the degree of similarity in the epi-signatures of some CSS subtypes and NCBRS can be greater than that within CSS, indicating a link in the functional basis of the two syndromes. We show that chromosome 6q25 microdeletion syndrome, harboring ARID1B deletions, exhibits a similar CSS/NCBRS methylation profile. Specificity of this epi-signature was confirmed across a wide range of neurodevelopmental conditions including other chromatin remodeling and epigenetic machinery disorders. We demonstrate that a machine-learning model trained on this DNA methylation profile can resolve ambiguous clinical cases, reclassify those with variants of unknown significance, and identify previously undiagnosed subjects through targeted population screening.

Genetic variation at the calcium-sensing receptor (CASR) locus: implications for clinical molecular diagnostics.

OBJECTIVES: The calcium-sensing receptor (CASR) is critical for maintenance of blood calcium in a narrow physiologic range. Naturally occurring mutations in the calcium-sensing receptor gene (CASR) cause hypocalcaemia or hypercalcaemia, and molecular diagnosis of these mutations is clinically important. Knowledge of SNP frequency and haplotype structure is essential in understanding molecular test results. DESIGN AND METHODS: Genotyping and haplotype analysis of 26 CASR SNPs (and a tetranucleotide insertion/deletion polymorphism) in control cohorts of Caucasian, Asian and African-American origin (n=1136, 88 and 104 chromosomes, respectively). RESULTS: The three SNPs in exon 7 (A986S, R990G, Q1011E) are the only common exonic variants in our cohorts, and synonymous exonic SNPs are uncommon. Linkage disequilibrium analysis of the Caucasian cohort (Haploview) showed that the CASR locus is divided into three haplotype blocks, coincident with 5' regulatory, coding, and 3' regulatory domains. CONCLUSIONS: These analyses provide an important framework for appropriate interpretation of CASR mutation screening now offered by a number of laboratories for the diagnosis of calcium disorders. They will assist in the study of CASR polymorphisms as predictors of complex disease states.

Germ-line DICER1 mutations do not make a major contribution to the etiology of familial testicular germ cell tumours.

BACKGROUND: The RNase III enzyme DICER1 plays a central role in maturation of microRNAs. Identification of neoplasia-associated germ-line and somatic mutations in DICER1 indicates that mis-expression of miRNAs in cancer may result from defects in their processing. As part of a recent study of DICER1 RNase III domains in 96 testicular germ cell tumors, a single RNase IIIb domain mutation was identified in a seminoma. To further explore the importance of DICER1 mutations in the etiology of testicular germ cell tumors (TGCT), we studied germ-line DNA samples from 43 probands diagnosed with familial TGCT. FINDINGS: We carried out High Resolution Melting Curve Analysis of DICER1 exons 2-12, 14-19, 21 and 24-27. All questionable melt curves were subjected to confirmatory Sanger sequencing.Sanger sequencing was used for exons 13, 20, 22 and 23. Intron-exon boundaries were included in all analyses. We identified 12 previously reported single nucleotide polymorphisms and two novel single nucleotide variants. No likely deleterious variants were identified; notably no mutations that were predicted to truncate the protein were identified. CONCLUSIONS: Taken together with previous studies, the findings reported here suggest a very limited role for either germ-line or somatic DICER1 mutations in the etiology of TGCT.

Evaluation of the warfarin-resistance polymorphism, VKORC1 Asp36Tyr, and its effect on dosage algorithms in a genetically heterogeneous anticoagulant clinic.

OBJECTIVES: To assess allele frequency and potential predictive value of recurrent polymorphisms affecting warfarin metabolism in an unselected patient cohort attending an anticoagulant clinic (n=186). DESIGN AND METHODS: Genotyping of ten SNPs in five candidate genes (VKORC1, CYP2C9, CALU, EPHX and GGCX) was carried out by ABI PRISM SNaPshot multiplex method. RESULTS: We confirm the association between high-frequency SNPs, VKORC1 c.-1639G>A and CYP2C9 *2/*3 and warfarin sensitivity, and contribute additional evidence that the VKORC1 p.Asp36Tyr variant is recurrent and independently associated with warfarin resistance in our population. Other SNPs made little contribution. CONCLUSION: Warfarin sensitivity was predicted by known VKORC1 and CYP2C9 SNPs. However, resistance associated with p.Asp36Tyr in VKORC1 would not be predicted by the usual markers. Despite its relatively low frequency (3/186 or 1.6%) clinical considerations may warrant its inclusion in pharmacogenetic screening for initial warfarin dosing in clinic populations with a heterogeneous population base.

Genetic determinants of extracellular magnesium concentration: analysis of multiple candidate genes, and evidence for association with the estrogen receptor alpha (ESR1) locus.

BACKGROUND: Serum magnesium concentration is a quantitative trait with substantial heritability. Although the pool of candidate genes continues to grow, only the histocompatibility locus has been associated with magnesium levels. To explore other possibilities, we targeted 6 candidate genes physiologically relevant to magnesium metabolism. METHODS: We studied a large cohort (n=471) derived from a well-characterized population of healthy Caucasian women 18 to 35 years. Total serum magnesium and calcium were measured by atomic absorption spectrophotometry (aaMg & aaCa). Genomic DNA was amplified and SNPs in candidate genes (CASR, VDR, ESR1, CLDN16, EGF1, TRPM6) genotyped by routine methods. RESULTS: We found a significant association between estrogen receptor alpha (ESR1) polymorphisms, PvuII and XbaI, and magnesium (r=-0.116, p=0.012 and r=-0.126, p=0.006, respectively). Stratifying by PvuII genotype (P/p alleles), the mean adjusted total magnesium (aaMg) concentration was significantly higher (p=0.01) in the pp group (0.823+/-0.005 mmol/l, n=130) than in PP homozygotes (0.805+/-0.006 mmol/l, n=70), and the mean in Pp heterozygotes was intermediate (0.810+/-0.005 mmol/l, n=180). No significant associations were observed with the other candidate genes tested. CONCLUSIONS: The significant association between magnesium and ESR1 polymorphisms supports previous studies linking physiologic changes in serum magnesium to estrogen status.

Calcium-sensing receptor mutations and denaturing high performance liquid chromatography.

The calcium-sensing receptor (CASR), a plasma membrane G-protein-coupled receptor, is expressed in parathyroid gland and kidney, and controls systemic calcium homeostasis. Inactivating CASR mutations are associated with familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism, and activating mutations cause autosomal dominant hypocalcemia (ADH). CASR mutation identification plays an important role in the clinical management of mineral metabolism disorders. We describe here a high-throughput method using screening with denaturing high performance liquid chromatography (DHPLC) to initially interrogate 12 amplicons covering translated exons and exon/intron boundaries, followed by sequencing of any amplicon with a modified melting curve relative to wild type, and direct sequencing of a 13th amplicon encoding the COOH-terminal tail to distinguish causative mutations from three common missense single nucleotide polymorphisms. A blinded analysis of 32 positive controls representing mutations throughout the CASR sequence, as well as 22 negative controls, yielded a concordance rate of 100%. We report eight novel and five recurrent FHH mutations, along with six novel and two recurrent ADH mutations. Thus, DHPLC provides a rapid and effective means to screen for CASR mutations.