News Article | April 18, 2016
Thanks in part to the efforts of one dedicated mother, who took to Facebook to document her son’s mysterious developmental disability, an international team of researchers led by scientists at UC San Francisco and Baylor College of Medicine in Houston has now identified a new genetic syndrome that could help illuminate the biological causes of one of the most common forms of intellectual disability. In a study of 10 children published online in the American Journal of Human Genetics on April 14, the researchers linked a constellation of birth defects affecting the brain, eye, ear, heart and kidney to mutations in a single gene, called RERE. The discovery is likely to aid researchers striving to understand the cause of birth defects more broadly, the study’s authors said, but it is also a boon to families who know for the first time the reason their children share this group of developmental disabilities. “Just having an answer can be hugely beneficial for families,” said co-senior author Elliott Sherr, M.D., Ph.D., a UCSF pediatric neurologist who directs the Brain Development Research Program and the Comprehensive Center for Brain Development at UCSF. “Of course, getting a genetic answer is just the first step, but for the longest time we didn’t even have that much. It gives these families hope that we can move forward.” Finding could speed search for answers in more common genetic syndrome In their paper, the researchers demonstrate that the developmental disabilities suffered by children with RERE mutations correspond almost perfectly to the well-known pattern of intellectual disabilities, heart defects, craniofacial abnormalities, and hearing and vision problems seen in 1p36 deletion syndrome, one of the most common sources of intellectual disability in children. This syndrome occurs in approximately 1 in 5,000 newborns, and is caused by a much larger (and harder to study) pattern of genetic damage in the so-called 1p36 region at the tip of human chromosome 1. The research group of Daryl Scott, MD, PHD, an associate professor of molecular and human genetics at Baylor College of Medicine, has been working for many years to identify the specific genes that cause the medical problems in children with 1p36 deletion syndrome. “Previous research had narrowed it down to two smaller ‘critical regions’ within the 1p36 region, but even these smaller regions contain dozens of different genes,” said Scott, who was co-senior author on the new study. Scott’s group had focused on the RERE gene, which lies within one of these 1p36 critical regions, because it plays a role in retinoic acid (vitamin A) signaling, an important pathway regulating the development of many organs, including the brain, eye and heart. The Baylor researchers found that mice with Rere mutations had birth defects that were very similar to the children with 1p36 deletions, but had initially been unable to prove that damage to this gene was sufficient produce the same developmental problems in humans. Sherr and Scott credit the genesis of their collaboration to Chauntelle Trefz, the mother of one of Sherr’s patients who connected the two researchers after discovering Scott’s work on mice with Rere mutations online and whose Facebook page about her son, Harrison, became a hub for identifying other children with the same condition. Trefz says that getting the whole exome sequencing results from Sherr and learning that a single gene mutation was responsible for her son’s dizzying array of symptoms — which include global developmental delay, vision problems, hearing problems, weak muscles, and constant acid reflux — was “a game-changer.” “Learning about the mutation was like a huge weight had been lifted,” she said. “When you bring a child with special needs into the world you feel so guilty, like you’ve done something wrong. Hope can be a hard thing to find. Dr. Sherr gave us hope.” Trefz started a Facebook page documenting the joys and challenges of raising and caring for Harrison, who is now 4, hoping to find other families whose children had the same condition. “Harrison is such a happy kid, and he seems normal in many ways, but he’s really not,” she said. “I could see a lot of kids falling through the cracks without the right diagnosis. I wanted other parents to see this and say, ‘that sounds like my son.’” Soon Sherr and Scott had identified 10 children with RERE mutations through collaborators around the US, as well as several from the Netherlands who had found the researchers through Trefz’s Facebook page. The researchers began a thorough comparison of these 10 children with a cohort of 31 patients with the more common 1p36 deletion syndrome, and found that RERE mutations alone produced almost exactly the same pattern of symptoms as 1p36 syndrome, with the exception of a few of the craniofacial abnormalities and cardiomyopathies often seen in that more common syndrome. Additional experiments showed that unique brain and eye problems first observed in human patients were also seen in the mice with Rere mutations. “It’s still a shock that [a mutation in] one gene is capable of causing all these different problems,” Scott said. “But this finding really brings everything together, from molecular studies to mouse experiments and all the way to human patients. We’ve finally proved what we’ve been talking about for all these years.” Though much more study is needed to understand the syndrome fully, Scott said, RERE mutations may be capable of inducing a diverse set of developmental problems because the protein encoded by the gene interacts with important developmental processes in many organs throughout the body, such as the retinoic acid signaling crucial for proper eye and heart development. When RERE doesn’t function properly, the development of all of these organs is affected. Sherr acknowledges that the current sample of just 10 patients with RERE mutations, who each experience slightly different symptoms with notably different levels of severity, is too small to give a complete portrait of the new syndrome. “Now that we’ve seen the first 10 cases, we want to know what the next 10, the next 20 look like,” he said. “That may not take very long. Before we’d even published the paper, we’d already gotten calls from more clinics around the country whose patients have similar mutations. We suspect this syndrome may be significantly more common than we previously appreciated.” The empowerment of families through social media and the plummeting cost of of gene sequencing technologies have produced a revolution in the pace of discovery about rare genetic conditions, Sherr said. “In the last five years alone there’s been a huge explosion in the number of conditions we can decipher genetically – we can take a few kids with developmental disabilities, come up with a coherent genetic explanation for what has happened and use that as first step for how to move forward” he said. “When I started working in child neurology as a fellow back in the late ‘90s, we understood just a few of these super-rare genetic disorders but now there are hundreds. And we’re just getting started.” The authors acknowledge the following industry ties: Sherr is a member of the clinical advisory board of genetic testing company InVitae and consults for Personalis. Four of the authors are employees of GeneDx, which provides exome sequencing on a clinical basis. The Department of Molecular and Human Genetics at Baylor College of Medicine derives revenue from clinical laboratory testing conducted at Baylor Miraca Genetics Laboratories, which provides exome sequencing on a clinical basis.
PubMed | Retina and Vitreous of Texas, Jiangmen Maternity and Child Health Care Hospital, Peking Union Medical College, Baylor Miraca Genetics Laboratories and Baylor College of Medicine
Type: Journal Article | Journal: The Journal of molecular diagnostics : JMD | Year: 2016
Retinitis pigmentosa (RP) is the most common form of retinal dystrophy. The disease is characterized by the progressive degeneration of photoreceptors, ultimately leading to blindness. The exon ORF15 of RPGTPase regulator (RPGR) is a mutation hot spot for X-linked RP and one form of cone dystrophy. However, accurate molecular testing of ORF15 is challenging because of a large segment of highlyrepetitive purine-rich sequence in this exon. ORF15 performs poorly in next-generationsequencing-based panels or whole exome sequencing analysis, whereas Sanger sequencing of ORF15 requires special reagents and PCR conditions with multiple pairs of overlapping primers that often do not provide a clean sequence. Because of these technical difficulties, molecular analysis of ORF15 is performed mostly in research laboratories without validation for clinical application. Herein, we report the development of a single step of high-fidelity PCR followed by next-generation sequencing for accurate mutation detection, which is easily integrated into routine clinical practice. Our approach has improved coverage depth of ORF15 with the ability to detect single-nucleotide variants and deletions/duplications. Using this method, we were able to identify ORF15 pathogenic variants in approximately 31% of undiagnosed RP patients. Our results underline the clinical importance of complete and accurate sequence analysis of ORF15 for patients with retinal dystrophies.
PubMed | Childrens Hospital Los Angeles, New York University, Baylor College of Medicine, Wayne State University and 3 more.
Type: Case Reports | Journal: PLoS genetics | Year: 2016
Genetic leukoencephalopathies (gLEs) are a group of heterogeneous disorders with white matter abnormalities affecting the central nervous system (CNS). The causative mutation in ~50% of gLEs is unknown. Using whole exome sequencing (WES), we identified homozygosity for a missense variant, VPS11: c.2536T>G (p.C846G), as the genetic cause of a leukoencephalopathy syndrome in five individuals from three unrelated Ashkenazi Jewish (AJ) families. All five patients exhibited highly concordant disease progression characterized by infantile onset leukoencephalopathy with brain white matter abnormalities, severe motor impairment, cortical blindness, intellectual disability, and seizures. The carrier frequency of the VPS11: c.2536T>G variant is 1:250 in the AJ population (n = 2,026). VPS11 protein is a core component of HOPS (homotypic fusion and protein sorting) and CORVET (class C core vacuole/endosome tethering) protein complexes involved in membrane trafficking and fusion of the lysosomes and endosomes. The cysteine 846 resides in an evolutionarily conserved cysteine-rich RING-H2 domain in carboxyl terminal regions of VPS11 proteins. Our data shows that the C846G mutation causes aberrant ubiquitination and accelerated turnover of VPS11 protein as well as compromised VPS11-VPS18 complex assembly, suggesting a loss of function in the mutant protein. Reduced VPS11 expression leads to an impaired autophagic activity in human cells. Importantly, zebrafish harboring a vps11 mutation with truncated RING-H2 domain demonstrated a significant reduction in CNS myelination following extensive neuronal death in the hindbrain and midbrain. Thus, our study reveals a defect in VPS11 as the underlying etiology for an autosomal recessive leukoencephalopathy disorder associated with a dysfunctional autophagy-lysosome trafficking pathway.
PubMed | University of Washington, Regional Medical Center, Baylor College of Medicine, Stanford University and 5 more.
Type: Journal Article | Journal: American journal of human genetics | Year: 2016
The underlying genetic etiology of rhabdomyolysis remains elusive in a significant fraction of individuals presenting with recurrent metabolic crises and muscle weakness. Using exome sequencing, we identified bi-allelic mutations in TANGO2 encoding transport and Golgi organization 2 homolog (Drosophila) in 12 subjects with episodic rhabdomyolysis, hypoglycemia, hyperammonemia, and susceptibility to life-threatening cardiac tachyarrhythmias. A recurrent homozygous c.460G>A (p.Gly154Arg) mutation was found in four unrelated individuals of Hispanic/Latino origin, and a homozygous 34 kb deletion affecting exons 3-9 was observed in two families of European ancestry. One individual of mixed Hispanic/European descent was found to be compound heterozygous for c.460G>A (p.Gly154Arg) and the deletion of exons 3-9. Additionally, a homozygous exons 4-6 deletion was identified in a consanguineous Middle Eastern Arab family. No homozygotes have been reported for these changes in control databases. Fibroblasts derived from a subject with the recurrent c.460G>A (p.Gly154Arg) mutation showed evidence of increased endoplasmic reticulum stress and a reduction in Golgi volume density in comparison to control. Our results show that the c.460G>A (p.Gly154Arg) mutation and the exons 3-9 heterozygous deletion in TANGO2 are recurrent pathogenic alleles present in the Latino/Hispanic and European populations, respectively, causing considerable morbidity in the homozygotes in these populations.
Westerfield L.E.,Baylor College of Medicine |
Stover S.R.,Baylor College of Medicine |
Mathur V.S.,Baylor College of Medicine |
Nassef S.A.,Baylor College of Medicine |
And 6 more authors.
Prenatal Diagnosis | Year: 2015
Objective: Diagnostic whole exome sequencing (WES) is rapidly entering clinical genetics, but experience with reproductive genetic counseling aspects is limited. The purpose of this study was to retrospectively review and report on our experience with preconception and prenatal genetic counseling for diagnostic WES. Method: We performed a retrospective chart review over 34months in a large private prenatal genetic counseling practice and analyzed data for referral indications, findings, and results of genetic counseling related to diagnostic WES. Results: Ten of 14 patients counseled about diagnostic WES for ongoing pregnancies pursued the test, resulting in identification of three pathogenic variants (30%). Five of 15 patients seeking counseling about familial WES results in an affected proband pursued prenatal diagnosis, resulting in identification of one affected fetus and five unaffected fetuses. We experienced challenges related to complexity and uncertainty of results, turnaround time, cost and insurance overage, and multidisciplinary fetal care coordination. Conclusion: Despite having experienced complexity and identified challenges of the reproductive genetic counseling, availability of diagnostic WES contributed important information that aided in prenatal care planning and decision-making. Future enhanced provider education and larger studies to systematically study the integration of WES in reproductive genetic counseling and prenatal care will be important. © 2015 John Wiley & Sons, Ltd.
PubMed | Stanford University and Baylor Miraca Genetics Laboratories
Type: Journal Article | Journal: Cold Spring Harbor molecular case studies | Year: 2017
Here we describe a patient who presented with a history of congenital diaphragmatic hernia, inguinal hernia, and recurrent umbilical hernia. She also has joint laxity, hypotonia, and dysmorphic features. A unifying diagnosis was not identified based on her clinical phenotype. As part of her evaluation through the Undiagnosed Diseases Network, trio whole-exome sequencing was performed. Pathogenic variants in
PubMed | Baylor Miraca Genetics Laboratories, Yakima Valley Memorial Hospital and Baylor College of Medicine
Type: Journal Article | Journal: The Journal of molecular diagnostics : JMD | Year: 2015
Germline mutations in the DNA mismatch repair gene PMS2 underlie the cancer susceptibility syndrome, Lynch syndrome. However, accurate molecular testing of PMS2 is complicated by a large number of highly homologous sequences. To establish a comprehensive approach for mutation detection of PMS2, we have designed a strategy combining targeted capture next-generation sequencing (NGS), multiplex ligation-dependent probe amplification, and long-range PCR followed by NGS to simultaneously detect point mutations and copy number changes of PMS2. Exonic deletions (E2 to E9, E5 to E9, E8, E10, E14, and E1 to E15), duplications (E11 to E12), and a nonsense mutation, p.S22*, were identified. Traditional multiplex ligation-dependent probe amplification and Sanger sequencing approaches cannot differentiate the origin of the exonic deletions in the 3 region when PMS2 and PMS2CL share identical sequences as a result of gene conversion. Our approach allows unambiguous identification of mutations in the active gene with a straightforward long-range-PCR/NGS method. Breakpoint analysis of multiple samples revealed that recurrent exon 14 deletions are mediated by homologous Alu sequences. Our comprehensive approach provides a reliable tool foraccurate molecular analysis of genes containing multiple copies of highly homologous sequences and should improve PMS2 molecular analysis for patients with Lynch syndrome.
PubMed | University of Nebraska Medical Center, Baylor Miraca Genetics Laboratories and Baylor College of Medicine
Type: Journal Article | Journal: Genetics in medicine : official journal of the American College of Medical Genetics | Year: 2016
Next-generation sequencing (NGS) has been widely applied to clinical diagnosis. Target-gene capture followed by deep sequencing provides unbiased enrichment of the target sequences, which not only accurately detects single-nucleotide variations (SNVs) and small insertion/deletions (indels) but also provides the opportunity for the identification of exonic copy-number variants (CNVs) and large genomic rearrangements.Capture NGS has the ability to easily detect SNVs and small indels. However, genomic changes involving exonic deletions/duplications and chromosomal rearrangements require more careful analysis of captured NGS data. Misaligned raw sequence reads may be more than just bad data. Some mutations that are difficult to detect are filtered by the preset analytical parameters. Loose filtering and alignment conditions were used for thorough analysis of the misaligned NGS reads. Additionally, using an in-house algorithm, NGS coverage depth was thoroughly analyzed to detect CNVs.Using real examples, this report underscores the importance of the accessibility to raw sequence data and manual review of suspicious sequence regions to avoid false-negative results in the clinical application of NGS. Assessment of the NGS raw data generated by the use of loose filtering parameters identified several sequence aberrations, including large indels and genomic rearrangements. Furthermore, NGS coverage depth analysis identified homozygous and heterozygous deletions involving single or multiple exons.Our results demonstrate the power of deep NGS in the simultaneous detection of point mutations and intragenic exonic deletion in one comprehensive step.Genet Med 18 5, 513-521.
PubMed | McGill University, Baylor Miraca Genetics Laboratories and Baylor College of Medicine
Type: Journal Article | Journal: Molecular genetics and metabolism | Year: 2016
Next generation sequencing (NGS) based gene panel testing is increasingly available as a molecular diagnostic approach for inborn errors of metabolism. Over the past 40 years patients have been referred to the Vitamin B12 Clinical Research Laboratory at McGill University for diagnosis of inborn errors of cobalamin metabolism by functional studies in cultured fibroblasts. DNA samples from patients in which no diagnosis was made by these studies were tested by a NGS gene panel to determine whether any molecular diagnoses could be made. 131 DNA samples from patients with elevated methylmalonic acid and no diagnosis following functional studies of cobalamin metabolism were analyzed using the 24 gene extended cobalamin metabolism NGS based panel developed by Baylor Miraca Genetics Laboratories. Gene panel testing identified two or more variants in a single gene in 16/131 patients. Eight patients had pathogenic findings, one had a finding of uncertain significance, and seven had benign findings. Of the patients with pathogenic findings, five had mutations in ACSF3, two in SUCLG1 and one in TCN2. Thus, the NGS gene panel allowed for the presumptive diagnosis of 8 additional patients for which a diagnosis was not made by the functional assays.
PubMed | Texas Childrens Hospital, The Jackson Laboratory, Baylor Miraca Genetics Laboratories and Baylor College of Medicine
Type: Journal Article | Journal: American journal of medical genetics. Part A | Year: 2016
Mutations in CRIPT encoding cysteine-rich PDZ domain-binding protein are rare, and to date have been reported in only two patients with autosomal recessive primordial dwarfism and distinctive facies. Here, we describe a female with biallelic mutations in CRIPT presenting with postnatal growth retardation, global developmental delay, and dysmorphic features including frontal bossing, high forehead, and sparse hair and eyebrows. Additional clinical features included high myopia, admixed hyper- and hypopigmented macules primarily on the face, arms, and legs, and syndactyly of 4-5 toes bilaterally. Using whole exome sequencing (WES) and chromosomal microarray analysis (CMA), we detected a c.8G>A (p.C3Y) missense variant in exon 1 of the CRIPT gene inherited from the mother and a 1,331bp deletion encompassing exon 1, inherited from the father. The c.8G>A (p.C3Y) missense variant in CRIPT was apparently homozygous in the proband due to the exon 1 deletion. Our findings illustrate the clinical utility of combining WES with copy number variant (CNV) analysis to provide a molecular diagnosis to patients with rare Mendelian disorders. Our findings also illustrate the clinical spectrum of CRIPT related mutations. 2016 Wiley Periodicals, Inc.