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Clinical Focus

  • Perinatal Genetics
  • Genetics of Recurrent Pregnancy Loss & Infertility
  • Differences of Sexual Development
  • Dysmorphology
  • Diagnostic Tools & Methodology
  • Clinical Genetics

Administrative Appointments

  • Associate Director, Perinatal Genetics (2017 - Present)
  • Clerkship Director, Division of Medical Genetics (2018 - Present)

Boards, Advisory Committees, Professional Organizations

  • Member, American Society of Human Genetics (2014 - Present)
  • Membership Committee, American College of Medical Genetics and Genomics (2015 - Present)

Professional Education

  • Board Certification: American Board of Medical Genetics and Genomics, Clinical Genetics (2017)
  • Residency: University of Washington Medical Center (2016) WA
  • Residency: University of Texas at Austin (2014) TX
  • Medical Education: University of Iowa Carver College of Medicine (2012) IA


All Publications

  • How geneticists think about Differences/Disorders of Sexual Development (DSD): A conversation. Journal of pediatric urology Byers, H. M., Fossum, M., Wu, H. 2020


    A multidisciplinary DSD clinic offers the opportunity for different specialties to learn from each other, as each provides their own perspective and expertise to the management of these complex patients, leading to collaborative care. For the patient, a multi-disciplinary clinic can improve access to care and decrease stress, as patients see all of the specialists on one day. For urologists seeing patients with DSD within a multi-disciplinary DSD clinic as well as independently, understanding what other specialists provide can help facilitate care and referral. Medical genetics is part of a multi-disciplinary DSD clinic. Given the recent advances in genetic diagnostics, many of the offered tests may be less familiar to the pediatric urologist. Therefore, this conversation reviews the clinical presentations and genetic testing options including chromosomal microarray, genetic testing panel, whole exome sequencing, and whole genome sequencing and how these can be helpful in the diagnosis and management of patients with DSD conditions.

    View details for DOI 10.1016/j.jpurol.2020.08.015

    View details for PubMedID 32893165

  • Medical genetics education in the midst of the COVID-19 pandemic: Shared resources. American journal of medical genetics. Part A Regier, D. S., Smith, W. E., Byers, H. M. 2020


    In the midst of the COVID-19 pandemic, it is appropriate that our focus is on patient care and preparation. However, the genetics community is well poised to fill in the educational gap created by medical students transitioning to limiting patient contact, creation of telemedicine patient care, and online learning modules. Our history of agility in learning and teaching is now only inhibited by the time constraints of current clinical demands on the genetics community. This publication is designed to offer ideas and resources for quickly transitioning our education to meet the current demands in the time of a pandemic. Not only will this allow us to continue our strong history of education, it will enhance our strong commitment to using modern educational techniques and tools to address the genetics workforce issues that have defined the recent past. We have the opportunity to aggressively educate for trainees that now have the capacity to learn, and to lead the way in showing how the genetics community rallies together no matter the challenge.

    View details for DOI 10.1002/ajmg.a.61595

    View details for PubMedID 32323908

  • The Impact of Rapid Exome Sequencing on Medical Management of Critically Ill Children. The Journal of pediatrics Freed, A. S., Clowes Candadai, S. V., Sikes, M. C., Thies, J. n., Byers, H. M., Dines, J. N., Ndugga-Kabuye, M. K., Smith, M. B., Fogus, K. n., Mefford, H. C., Lam, C. n., Adam, M. P., Sun, A. n., McGuire, J. K., DiGeronimo, R. n., Dipple, K. M., Deutsch, G. H., Billimoria, Z. C., Bennett, J. T. 2020


    To evaluate the clinical utility of rapid exome sequencing (rES) in critically ill children with likely genetic disease using a standardized process at a single institution. To provide evidence that rES with should become standard of care for this patient population.We implemented a process to provide clinical-grade rES to eligible children at a single institution. Eligibility included: a) recommendation of rES by a consulting geneticist, b) monogenic disorder suspected, c) rapid diagnosis predicted to affect inpatient management, d) pre-test counseling provided by an appropriate provider, and e) unanimous approval by a committee of 4 geneticists. Trio exome sequencing was sent to a reference laboratory that provided verbal report within 7-10 days. Clinical outcomes related to rES were prospectively collected. Input from geneticists, genetic counselors, pathologists, neonatologists and critical care pediatricians was collected to identify changes in management related to rES.54 patients were eligible for rES over a 34 month study period. 46 of these underwent rES, 24 of which (52%) had at least one change in management related to rES. In 20 (43%) patients a molecular diagnosis was achieved, demonstrating that non-diagnostic exomes could change medical management in some cases. 84% were under 1 month old at rES request and mean turnaround time was 9 days.rES testing has a significant impact on the management of critically ill children with suspected monogenic disease and should be considered standard of care for tertiary institutions who can provide coordinated genetics expertise.

    View details for DOI 10.1016/j.jpeds.2020.06.020

    View details for PubMedID 32553838

  • Factor VIII and vWF deficiency in STT3A-CDG. Journal of inherited metabolic disease Chang, I. J., Byers, H. M., Ng, B. G., Merritt, J. L., Gilmore, R., Shrimal, S., Wei, W., Zhang, Y., Blair, A. B., Freeze, H. H., Zhang, B., Lam, C. 2018


    STT3A-CDG (OMIM# 615596) is an autosomal recessive N-linked glycosylation disorder characterized by seizures, developmental delay, intellectual disability, and a type I carbohydrate deficient transferrin pattern. All previously reported cases (n=6) have been attributed to a homozygous pathogenic missense variant c.1877C>T (p.Val626Ala) in STT3A. We describe a patient with a novel homozygous likely pathogenic missense variant c.1079A>C (p.Tyr360Ser) who presents with chronically low Factor VIII (FVIII) and von Willebrand Factor (vWF) levels and activities in addition to the previously reported symptoms of developmental delay and seizures. VWF in our patient's plasma is present in a mildly hypoglycosylated form. FVIII antigen levels were too low to quantify in our patient. Functional studies with STT3A-/- HEK293 cells showed severely reduced FVIII antigen and activity levels in conditioned media <10% expected, but normal intracellular levels. We also show decreased glycosylation of STT3A-specific acceptors in fibroblasts from our patient, providing a mechanistic explanation for how STT3A deficiency leads to a severe defect in FVIII secretion. Our results suggest that certain STT3A-dependent N-glycans are required for efficient FVIII secretion, and the decreased FVIII level in our patient is a combined effect of both severely impaired FVIII secretion and lower plasma VWF level. Our report expands both the genotype and phenotype of STT3A-CDG; demonstrating, as in most types of CDG, that there are multiple disease-causing variants in STT3A.

    View details for PubMedID 30701557

  • Discordant sex between fetal screening and postnatal phenotype requires evaluation. Journal of perinatology : official journal of the California Perinatal Association Byers, H. M., Neufeld-Kaiser, W., Chang, E. Y., Tsuchiya, K., Oehler, E. S., Adam, M. P. 2018


    OBJECTIVE: Non-invasive prenatal screening (NIPS) utilizes circulating cell-free DNA (cfDNA) to screen for fetal genetic abnormalities. NIPS is the first widely-available prenatal screen to assess genotypic sex. Most pediatricians have limited familiarity with NIPS technology and potential etiologies of discordant results. Increased familiarity may provide diagnostic insight and improve clinical care.STUDY DESIGN: We reviewed all patients with discordant genotypic fetal sex assessed by cfDNA and neonatal phenotypic sex referred to our medical center.RESULT: Four infants with discordant cfDNA result and phenotypic sex were identified. Etiologies include vanishing twin syndrome, difference of sexual development, sex chromosome aneuploidy and maternal chimerism.CONCLUSIONS: We present four cases illustrating potential etiologies of discordant cfDNA result and postnatal phenotypic sex. Unanticipated cfDNA results offer the perinatologist a unique opportunity for early diagnosis and targeted treatment of various conditions, many of which may not have otherwise been detected in the perinatal period.

    View details for PubMedID 30459335

  • Increasing the Participation of Pregnant Women in Clinical Trials. JAMA Heyrana, K., Byers, H. M., Stratton, P. 2018

    View details for PubMedID 30422300

  • Minimal mosaicism, maximal phenotype: Discordance between clinical and molecular findings in two patients with tuberous sclerosis. American journal of medical genetics. Part C, Seminars in medical genetics Byers, H. M., Jensen, D. M., Glass, I. A., Bennett, J. T. 2018


    Tuberous sclerosis complex (TSC) is an autosomal dominant neurocutaneous disorder characterized by hamartomatous growths in the brain, kidneys, lungs, skin, heart, and retina. TSC is caused by loss of function mutations in one of two tumor suppressor genes, TSC1 or TSC2. Two-thirds of individuals with TSC have de novo mutations, and individuals with postzygotic pathogenic variants in both TSC1 and TSC2 have been reported. The development of sensitive molecular methods, such as next generation sequencing, has led to an increased ability to detect low-level mosaic variants, which are typically thought to have milder phenotypes because a smaller fraction of cells in the body harbor the mutation. Here, we describe two patients with TSC who had severe phenotypic involvement, but only low-level mosaicism in TSC2. Given this apparent discrepancy and concern about a missed constitutional variant, we sampled multiple tissues in both cases to confirm these mosaic mutations. Sampling of multiple tissues can be crucial in molecular diagnosis of mosaic TSC. These cases highlight, in general, challenges in molecular diagnosis of genetic conditions due to postzygotic mutations.

    View details for PubMedID 30260069

  • Expanding the phenotype of congenital central hypoventilation syndrome impacts management decisions. American journal of medical genetics. Part A Byers, H. M., Chen, M., Gelfand, A. S., Ong, B., Jendras, M., Glass, I. A. 2018


    Congenital central hypoventilation syndrome (CCHS) is a neurocristopathy caused by pathogenic heterozygous variants in the gene paired-like homeobox 2b (PHOX2B). It is characterized by severe infantile alveolar hypoventilation. Individuals may also have diffuse autonomic nervous system dysfunction, Hirschsprung disease and neural crest tumors. We report three individuals with CCHS due to an 8-base pair duplication in PHOX2B; c.691_698dupGGCCCGGG (p.Gly234Alafs*78) with a predominant enteral and neural crest phenotype and a relatively mild respiratory phenotype. The attenuated respiratory phenotype reported here and elsewhere suggests an emergent genotype:phenotype correlation which challenges the current paradigm of invoking mechanical ventilation for all infants diagnosed with CCHS. Best treatment requires careful clinical judgment and ideally the assistance of a care team with expertise in CCHS.

    View details for PubMedID 29696799

  • Acute liver failure in neonates with undiagnosed hereditary fructose intolerance due to exposure from widely available infant formulas MOLECULAR GENETICS AND METABOLISM Li, H., Byers, H. M., Diaz-Kuan, A., Vos, M. B., Hall, P. L., Tortorelli, S., Singh, R., Wallenstein, M. B., Allain, M., Dimmock, D. P., Farrell, R. M., McCandless, S., Gambello, M. J. 2018; 123 (4): 428?32


    Hereditary fructose intolerance (HFI) is an autosomal recessive disorder caused by aldolase B (ALDOB) deficiency resulting in an inability to metabolize fructose. The toxic accumulation of intermediate fructose-1-phosphate causes multiple metabolic disturbances, including postprandial hypoglycemia, lactic acidosis, electrolyte disturbance, and liver/kidney dysfunction. The clinical presentation varies depending on the age of exposure and the load of fructose. Some common infant formulas contain fructose in various forms, such as sucrose, a disaccharide of fructose and glucose. Exposure to formula containing fructogenic compounds is an important, but often overlooked trigger for severe metabolic disturbances in HFI. Here we report four neonates with undiagnosed HFI, all caused by the common, homozygous mutation c.448G>C (p.A150P) in ALDOB, who developed life-threatening acute liver failure due to fructose-containing formulas. These cases underscore the importance of dietary history and consideration of HFI in cases of neonatal or infantile acute liver failure for prompt diagnosis and treatment of HFI.

    View details for PubMedID 29510902

  • Postmortem Somatic Sequencing of Tumors From Patients With Suspected Lynch Syndrome Has Clinical Utility for Surviving Relatives JCO Precision Oncology Byers, H. M., Jacobson, A., McFaddin, A. S., Ussakli, C. H., Newlin, A., Stanich, P. S., More, S., Hamblett, A., Tait, J., Shirts, B., Pritchard, C. C., Konnick, E. Q., Lockwood, C. M. 2018; 2 (1): 1-7

    View details for DOI 10.1200/PO.18.00108

  • Postmortem Somatic Sequencing of Tumors From Patients With Suspected Lynch Syndrome Has Clinical Utility for Surviving Relatives. JCO precision oncology Byers, H. M., Jacobson, A. n., McFaddin, A. S., Ussakli, C. H., Newlin, A. n., Stanich, P. P., More, S. n., Hamblett, A. n., Tait, J. F., Shirts, B. n., Pritchard, C. C., Konnick, E. Q., Lockwood, C. M. 2018; 2

    View details for DOI 10.1200/PO.18.00108

    View details for PubMedID 32913991

    View details for PubMedCentralID PMC7446443

  • Unexpected ethical dilemmas in sex assignment in 46,XY DSD due to 5-alpha reductase type 2 deficiency AMERICAN JOURNAL OF MEDICAL GENETICS PART C-SEMINARS IN MEDICAL GENETICS Byers, H. M., Mohnach, L. H., Fechner, P. Y., Chen, M., Thomas, I. H., Ramsdell, L. A., Shnorhavorian, M., McCauley, E. A., Oelschlager, A., Park, J. M., Sandberg, D. E., Adam, M. P., Keegan, C. E. 2017; 175 (2): 260?67


    Sex assignment at birth remains one of the most clinically challenging and controversial topics in 46,XY disorders of sexual development (DSD). This is particularly challenging in deficiency of 5-alpha reductase type 2 given that external genitalia are typically undervirilized at birth but typically virilize at puberty to a variable degree. Historically, most individuals with 5-alpha reductase deficiency were raised females. However, reports that over half of patients who underwent a virilizing puberty adopted an adult male gender identity have challenged this practice. Consensus guidelines on assignment of sex of rearing at birth are equivocal or favor male assignment in the most virilized cases. While a male sex of rearing assignment may avoid lifelong hormonal therapy and/or allow the potential for fertility, female sex assignment may be more consistent with external anatomy in the most severely undervirilized cases. Herein, we describe five patients with 46,XY DSD due 5-alpha-reductase type 2 deficiency, all with a severe phenotype. An inter-disciplinary DSD medical team at one of two academic centers evaluated each patient. This case series illustrates the complicated decision-making process of assignment of sex of rearing at birth in 5-alpha reductase type 2 deficiency and the challenges that arise when the interests of the child, parental wishes, recommendations of the medical team, and state law collide.

    View details for PubMedID 28544750

    View details for PubMedCentralID PMC5489130

  • Description of a new oncogenic mechanism for atypical teratoid rhabdoid tumors in patients with ring chromosome 22. American journal of medical genetics. Part A Byers, H. M., Adam, M. P., Lacroix, A., Leary, S. E., Cole, B., Dobyns, W. B., Mefford, H. C. 2017; 173 (1): 245-249


    Atypical teratoid rhabdoid tumors of the central nervous system are rare, highly malignant, embryonal tumors most often occurring in children under age 3 years. Most are due to a somatic change in tumor suppressor gene SMARCB1 followed by a second-hit, typically loss of heterozygosity, best detected on immunohistochemical staining. Despite the noteworthy genetic homogeneity of atypical teratoid rhabdoid tumors, relatively little is known about the oncogenic mechanisms that lead to biallelic inactivation of SMARCB1. Herein, we describe a patient with constitutional ring chromosome 22, Phelan-McDermid syndrome and atypical teratoid rhabdoid tumor of the brain. During mitosis, sister chromatids of a ring chromosome may form interlocking and dicentric rings, resulting in chromosomal loss, complex karyotypes, and ongoing somatic variation. We hypothesized that the inherent instability of the patient's ring chromosome could lead to mosaic monosomy chromosome 22, resulting in allelic inactivation of the tumor-suppressor gene SMARCB1 and AT/RT if a second-hit occurred. Utilizing high-density microarray technology to analyze peripheral blood and tumor tissue, we confirmed this oncogenic mechanism, previously undescribed in patients with atypical teratoid rhabdoid tumors. Our data demonstrate chromosomal loss as a consequence of ring chromosome instability serving as the first hit in oncogenesis. This rare but possibly under-recognized mechanism is important to note in children with ATRT and syndromic features. Further investigation is warranted to assess if this oncogenic mechanism has management and/or prognostic implications. 2016 Wiley Periodicals, Inc.

    View details for DOI 10.1002/ajmg.a.37993

    View details for PubMedID 27734605

  • Dramatic Response After Lamotrigine in a Patient With Epileptic Encephalopathy and a De Novo CACNA1A Variant PEDIATRIC NEUROLOGY Byers, H. M., Beatty, C. W., Hahn, S. H., Gospe, S. M. 2016; 60: 79-82


    Channelopathies are a group of monogenic disorders that affect a single ion channel and can result in neurological disease. While a rare cause of epilepsy, channelopathies offer unique insight to the molecular basis of epilepsy and treatment opportunities. Calcium homeostasis is tightly regulated by a series of interacting subunits. CACNA1A encodes the principal pore-forming subunit of the voltage-gated P/Q-type calcium channel, alpha1. Patients with epileptic encephalopathy due to pathogenic variants in CACNA1A have been previously described and are challenging to treat.We describe a child with epileptic encephalopathy, ataxia, cognitive impairment, and significant social-behavioral abnormalities due to a de novo pathogenic variant, p.S1373L in the CACNA1A gene. After failing zonisamide and divalproex sodium, she had a dramatic response to lamotrigine with a precipitous decrease in seizure frequency and severity. This improvement has persisted over one year.While classically thought to act at sodium channels, lamotrigine also modulates the activity of the P/Q-type calcium channel, making it a candidate for precision therapy for patients with epileptic encephalopathy due to CACNA1A pathogenic variants. The rarity and clinical heterogeneity of epilepsy due to variants in CACNA1A presents challenges to clinical diagnosis. However, genetic analysis for patients with epilepsy continues to expand; additional patients are likely to be identified molecularly. Lamotrigine should be considered as a first-line treatment in patients with epileptic encephalopathy due to pathogenic variants in CACNA1A.

    View details for DOI 10.1016/j.pediatrneurol.2016.03.012

    View details for Web of Science ID 000379889900013

    View details for PubMedID 27212419

  • Novel Report of Phosphoserine Phosphatase Deficiency in an Adult with Myeloneuropathy and Limb Contractures. JIMD reports Byers, H. M., Bennett, R. L., Malouf, E. A., Weiss, M. D., Feng, J., Scott, C. R., Jayadev, S. 2016; 30: 103-108


    Serine is a nonessential amino acid that plays a vital role in proper development and functioning of the central nervous system (CNS). Serine deficiency leads to microcephaly, intellectual disability, seizures, and psychomotor retardation in children and severe axonal neuropathy in adults. Serine deficiency syndrome is due to a deficiency of one of three enzymes in the endogenous serine biosynthesis pathway: phosphoglycerate dehydrogenase, phosphoserine transaminase, or, most rarely, phosphoserine phosphatase. Of critical importance to clinical care, serine deficiency syndrome is treatable. Herein, we describe the novel presentation of phosphoserine phosphatase deficiency in an adult. The patient had intrauterine growth restriction, lifelong intellectual disability, childhood onset epilepsy, and borderline microcephaly. In adulthood, she developed progressively severe lower extremity hypertonia, axonal neuropathy, and hand contractures. Neuropathy was complicated by non-healing wounds. Fasting plasma amino acids showed low serine and glycine. Molecular analysis revealed compound heterozygous mutations in phosphoserine phosphatase (PSPH). Treatment with oral serine resulted in improvement of plasma serine levels, decreased neuropathic pain, and subjective improvement in energy level. Although the first case of phosphoserine phosphatase deficiency was described nearly 20 years ago, only eight cases have been reported, all in children. This is the first report of phosphoserine phosphatase deficiency in an adult.

    View details for PubMedID 26589312

  • A proposed method to predict preterm birth using clinical data, standard maternal serum screening, and cholesterol AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY Alleman, B. W., Smith, A. R., Byers, H. M., Bedell, B., Ryckman, K. K., Murray, J. C., Borowski, K. S. 2013; 208 (6)


    The objective of the study was to create a predictive model for preterm birth (PTB) from available clinical data and serum analytes.Serum analytes and routine pregnancy screening plus cholesterol and corresponding health information were linked to birth certificate data for a cohort of 2699 Iowa women with serum sampled in the first and second trimester. Stepwise logistic regression was used to select the best predictive model for PTB.Serum screening markers remained significant predictors of PTB, even after controlling for maternal characteristics. The best predictive model included maternal characteristics, first-trimester total cholesterol, total cholesterol change between trimesters, and second-trimester alpha-fetoprotein and inhibin A. The model showed better discriminatory ability than PTB history alone and performed similarly in subgroups of women without past PTB.Using clinical and serum screening data, a potentially useful predictor of PTB was constructed. Validation and replication in other populations, and incorporation of other measures that identify PTB risk, like cervical length, can be a step toward identifying additional women who may benefit from new or currently available interventions.

    View details for DOI 10.1016/j.ajog.2013.03.005

    View details for Web of Science ID 000320596600020

    View details for PubMedID 23500456

  • Variations in CRHR1 are associated with persistent pulmonary hypertension of the newborn PEDIATRIC RESEARCH Byers, H. M., Dagle, J. M., Klein, J. M., Ryckman, K. K., McDonald, E. L., Murray, J. C., Borowski, K. S. 2012; 71 (2): 162-167


    Persistent pulmonary hypertension of the newborn (PPHN) is associated with substantial infant morbidity and mortality. Recently, genetic associations have been found in idiopathic pulmonary arterial hypertension.PPHN was significantly (P < 0.05) associated with genetic variants in corticotropin-releasing hormone (CRH) receptor 1, CRHR1 and CRH-binding protein, CRHBP. Association with CRHR1 rs4458044 passed the Bonferroni threshold for significance. No mutations were found in the bone morphogenetic protein receptor type II (BMPR2) gene.We describe previously unreported genetic associations between PPHN and CRHR1 and CRHBP. These findings may have implications for further understanding the pathophysiology of PPHN and treatment.We performed a family-based candidate gene study to examine a genetic association with PPHN and sequenced the BMPR2 gene in 72 individuals. We enrolled 110 families with infants diagnosed with PPHN based on inclusion criteria. After medical chart review, 22 subjects were excluded based on predefined criteria, and DNA samples from 88 affected infants and at least one parent per infant were collected and genotyped. Thirty-two single-nucleotide polymorphisms in 12 genes involved in vasoconstriction/vasodilation, lung development, surfactant regulation, or vascular endothelial cell function were investigated using family-based association tests.

    View details for DOI 10.1038/pr.2011.24

    View details for Web of Science ID 000303455000006

    View details for PubMedID 22258127

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