- Clinical Genetics
- Biochemical Genetics
Clinical Assistant Professor, Pediatrics - Medical Genetics
Program Director, Medical Biochemical Genetics Fellowship Program (2020 - Present)
Associate Program Director, Medical Biochemical Genetics Fellowship Program (2017 - 2020)
Honors & Awards
Phi Beta Kappa, Northwestern University (2001)
Summa cum laude, Northwestern University (2002)
Dr. Koch Memorial Scholarship Recipient, National PKU Alliance (2012)
Residency: Kaiser Permanente Northern California GME Programs (2011) CA
Internship: Kaiser Permanente Northern California GME Programs (2009) CA
Board Certification: American Board of Medical Genetics and Genomics, Clinical Biochemical Genetics (2015)
Board Certification: American Board of Medical Genetics and Genomics, Clinical Genetics (2013)
Fellowship: University of California, San Francisco (UCSF) (2014) CA
Residency: University of California, San Francisco (UCSF) (2013) CA
Board Certification: American Board of Pediatrics, Pediatrics (2011)
Medical Education: University of Illinois at Chicago (2008) IL
MITOCHONDRIAL-ATP6-ASSOCIATED DISEASE PRESENTS WITH DISTINCT PATTERN ON NEWBORN SCREENING: SHOULD IT BE INCLUDED AS A SECONDARY CONDITION?
ACADEMIC PRESS INC ELSEVIER SCIENCE. 2022: 247-248
View details for Web of Science ID 000772339900011
ANALYSIS OF URINE HEPARAN SULFATE AND ITS NON-REDUCING ENDS FOR THE FOLLOW-UP OF ABNORMAL NEWBORN SCREENING FOR MPS1
ACADEMIC PRESS INC ELSEVIER SCIENCE. 2022: 281-282
View details for Web of Science ID 000772339900069
Variable clinical severity in TANGO2 deficiency: Case series and literature review.
American journal of medical genetics. Part A
Biallelic pathogenic variants in the TANGO2 (transport and Golgi organization 2 homolog) gene have been identified as causing a rare metabolic disorder characterized by susceptibility to recurrent rhabdomyolysis, lactic acidosis, encephalopathy, and life-threatening tachyarrhythmias. Recently published reports suggest variable clinical severity and phenotypes. This study details five new patients from two families with biallelic pathogenic variants in the TANGO2 gene identified by whole exome sequencing and includes the largest number of affected individuals from a single family reported to date. We document significant intrafamilial variability and highlight that milder phenotypes may be underrecognized. We present biochemical and clinical data to help highlight the features that aid in consideration of this condition in the differential with disorders of fatty acid oxidation. We also present a comprehensive literature review summarizing the molecular, clinical, and biochemical findings for 92 individuals across 13 publications. Of the 27 pathogenic variants reported to date, the recurrent exons 3-9 deletion represents the most common variant seen in 42% of individuals with TANGO2 deficiency. Common clinical features seen in >70% of all individuals include acute metabolic crisis, rhabdomyolysis, neurologic abnormalities, developmental delay, and intellectual disability. Findings such as elevated creatine kinase, hypothyroidism, ketotic hypoglycemia, QT prolongation, or abnormalities of long-chain acylcarnitines and urine dicarboxylic acids should raise clinical suspicion for this life-threatening condition.
View details for DOI 10.1002/ajmg.a.62543
View details for PubMedID 34668327
Arginine to ornithine ratio as a diagnostic marker in patients with positive newborn screening for hyperargininemia.
Molecular genetics and metabolism reports
2021; 27: 100735
Arginase deficiency is a rare inborn error of metabolism that interrupts the final step of the urea cycle. Untreated individuals often present with episodic hyperammonemia, developmental delay, cognitive impairment, and spasticity in early childhood. The newborn screening (NBS) algorithms for arginase deficiency vary between individual states in the US but often include hyperargininemia and elevated arginine to ornithine (Arg/Orn) ratio. Here, we report 14 arginase deficiency cases, including two patients with positive NBS for hyperargininemia in whom the diagnosis of arginase deficiency was delayed owing to normal or near normal plasma arginine levels on follow-up testing. To improve the detection capability for arginase deficiency, we evaluated plasma Arg/Orn ratio as a secondary diagnostic marker in positive NBS cases for hyperargininemia. We found that plasma Arg/Orn ratio combined with plasma arginine was a better marker than plasma arginine alone to differentiate patients with arginase deficiency from unaffected newborns. In fact, elevated plasma arginine in combination with an Arg/Orn ratio of ≥1.4 identified all 14 arginase deficiency cases. In addition, we examined the impact of age on plasma arginine and ornithine levels. Plasma arginine increased 0.94mumol/L/day while ornithine was essentially unchanged in the first 31days of life, which resulted in a similar increasing trend for the Arg/Orn ratio (0.01/day). This study demonstrated that plasma Arg/Orn ratio as a secondary diagnostic marker improved the detection capability for arginase deficiency in newborns with hyperargininemia, which will allow timely detection of arginase deficiency and hence initiation of treatment before developing symptoms.
View details for DOI 10.1016/j.ymgmr.2021.100735
View details for PubMedID 33732618
- Profound neonatal lactic acidosis and renal tubulopathy in a patient with glycogen storage disease type IXa2 secondary to a de novo pathogenic variant in PHKA2 MOLECULAR GENETICS AND METABOLISM REPORTS 2021; 27
Unexpected diagnoses in patients with abnormal newborn screening
ACADEMIC PRESS INC ELSEVIER SCIENCE. 2021: S354
View details for Web of Science ID 000639219800534
- COVID-19 patient impact: A survey of the Gaucher community involving patients, caregivers and family members based in the US to determine impact of the pandemic ACADEMIC PRESS INC ELSEVIER SCIENCE. 2021: S93
Aicardi-Goutières syndrome may present with positive newborn screen for X-linked adrenoleukodystrophy.
American journal of medical genetics. Part A
We report three unrelated probands, two male and one female, diagnosed with Aicardi-Goutières syndrome (AGS) after screening positive on California newborn screening (CA NBS) for X-linked adrenoleukodystrophy (X-ALD) due to elevated C26:0 lysophosphatidylcholine (C26:0-LPC). Follow-up evaluation was notable for elevated C26:0, C26:1, and C26:0/C22:0 ratio, and normal red blood cell plasmalogens levels in all three probands. Diagnoses were confirmed by molecular sequencing prior to 12 months of age after clinical evaluation was inconsistent with X-ALD or suggestive of AGS. For at least one proband, the early diagnosis of AGS enabled candidacy for enrollment into a therapeutic clinical trial. This report demonstrates the importance of including AGS on the differential diagnosis for individuals who screen positive for X-ALD, particularly infants with abnormal neurological features, as this age of onset would be highly unusual for X-ALD. While AGS is not included on the Recommended Universal Screening Panel, affected individuals can be identified early through state NBS programs so long as providers are aware of a broader differential that includes AGS. This report is timely, as state NBS algorithms for X-ALD are actively being established, implemented, and refined.
View details for DOI 10.1002/ajmg.a.62160
View details for PubMedID 33683010
- MERRF GeneReviews/University of Washington Seattle. GeneReviews. 2021 ; GeneReviews
- Gaucher disease and SARS-CoV-2 infection: Emerging management challenges. Molecular genetics and metabolism 2020
Rare Saposin A deficiency: Novel variant and psychosine analysis.
Molecular genetics and metabolism
Saposin A is a post-translation product of the prosaposin (PSAP) gene that serves as an activator protein of the galactocerebrosidase (GALC) enzyme, and is necessary for the degradation of certain glycosphingolipids. Deficiency of saposin A leads to a clinical picture identical to that of early-infantile Krabbe disease caused by GALC enzyme deficiency. Galactosylsphingosine, also known as psychosine, is a substrate of the GALC enzyme that is known to be elevated in classic Krabbe disease. We present the case of an 18-month-old male with clinical and radiological findings concerning for Krabbe disease who had preserved GALC enzyme activity and negative GALC gene sequencing, but was found to have a homozygous variant, c.257 T > A (p.I86N), in the saposin A peptide of PSAP. Psychosine determination on dried blood spot at 18 months of age was elevated to 12 nmol/L (normal <3 nmol/L). We present this case to add to the literature on the rare diagnosis of atypical Krabbe disease due to saposin A deficiency, to report a novel presumed pathogenic variant within PSAP, and to suggest that individuals with saposin A deficiency may have elevated levels of psychosine, similar to children with classic Krabbe disease due to GALC deficiency.
View details for DOI 10.1016/j.ymgme.2019.08.001
View details for PubMedID 31439510
- TREATMENT WITH CHOLIC ACID LEADS TO RESOLUTION OF RENAL CYSTS IN CONGENITAL BILE ACID SYNTHESIS DISORDER TYPE I BMJ PUBLISHING GROUP. 2019: 208
Two de novo novel mutations in one SHANK3 allele in a patient with autism and moderate intellectual disability.
American journal of medical genetics. Part A
SHANK3 encodes for a scaffolding protein that links neurotransmitter receptors to the cytoskeleton and is enriched in postsynaptic densities of excitatory synapses. Deletions or mutations in one copy of the SHANK3 gene cause Phelan-McDermid syndrome, also called 22q13.3 deletion syndrome, a neurodevelopmental disorder with common features including global developmental delay, absent to severely impaired language, autistic behavior, and minor dysmorphic features. By whole exome sequencing, we identified two de novo novel variants including one frameshift pathogenic variant and one missense variant of unknown significance in a 14-year-old boy with delayed motor milestones, delayed language acquisition, autism, intellectual disability, ataxia, progressively worsening spasticity of the lower extremities, dysmorphic features, short stature, microcephaly, failure to thrive, chronic constipation, intrauterine growth restriction, and bilateral inguinal hernias. Both changes are within the CpG island in exon 21, separated by a 375 bp sequence. Next generation sequencing of PCR products revealed that the two variants are most frequently associated with each other. Sanger sequencing of the cloned PCR products further confirmed that both changes were on a single allele. The clinical presentation in this individual is consistent with other patients with a truncating mutation in exon 21, suggesting that the missense change contributes none or minimally to the phenotypes. This is the first report of two de novo mutations in one SHANK3 allele.
View details for PubMedID 29423971
- A NOVEL AUTOSOMAL DOMINANT SYNDROME RESULTING FROM VARIANTS IN CDC42 BMJ PUBLISHING GROUP. 2018: 170–71
Biochemical characteristics of newborns with carnitine transporter defect identified by newborn screening in California.
Molecular genetics and metabolism
Carnitine transporter defect (CTD; also known as systemic primary carnitine deficiency; MIM 212140) is due to mutations in the SLC22A5 gene and leads to extremely low carnitine levels in blood and tissues. Affected individuals may develop early onset cardiomyopathy, weakness, or encephalopathy, which may be serious or even fatal. The disorder can be suggested by newborn screening. However, markedly low newborn carnitine levels can also be caused by conditions unrelated to CTD, such as the low carnitine levels often associated with normal pregnancies and some metabolic disorders occurring in the mother. In order to clarify the biochemical characteristics most useful for identification of CTD in newborns, we examined California Department of Public Health newborn screening data for CTD from 2005 to 12 and performed detailed chart reviews at six metabolic centers in California. The reviews covered 14 cases of newborn CTD, 14 cases of maternal disorders (CTD, 6 cases; glutaric aciduria, type 1, 5; medium-chain acyl CoA dehydrogenase deficiency, 2; and cobalamin C deficiency, 1), and 154 false-positive cases identified by newborn screening. Our results show that newborns with CTD identified by NBS exhibit different biochemical characteristics, compared to individuals ascertained clinically. Newborns with CTD may have NBS dried blood spot free carnitine near the lower cutoff and confirmatory plasma total and free carnitine levels near the normal lower limit, particularly if obtained within two weeks after birth. These findings raise the concern that true cases of CTD may exist that could have been missed by newborn screening. CTD should be considered as a possible diagnosis in cases with suggestive clinical features, even if CTD was thought to be excluded in the newborn period. Maternal plasma total carnitine and newborn urine total carnitine values are the most important predictors of true CTD in newborns. However, biochemical testing alone does not yield a discriminant rule to distinguish true CTD from low carnitine in newborns due to other causes. Because of this biochemical variability and overlap, molecular genetic testing is imperative to confirm CTD in newborns. Additionally, functional testing of fibroblast carnitine uptake remains necessary for cases in which other confirmatory testing is inconclusive. Even with utilization of all available diagnostic testing methods, confirmation of CTD ascertained by NBS remains lengthy and challenging. Incorporation of molecular analysis as a second tier step in NBS for CTD may be beneficial and should be investigated.
View details for PubMedID 28711408
Molecular and clinical spectra of FBXL4 deficiency.
F-box and leucine-rich repeat protein 4 (FBXL4) is a mitochondrial protein whose exact function is not yet known. However, cellular studies have suggested that it plays significant roles in mitochondrial bioenergetics, mitochondrial DNA (mtDNA) maintenance, and mitochondrial dynamics. Biallelic pathogenic variants in FBXL4 are associated with an encephalopathic mtDNA maintenance defect syndrome that is a multisystem disease characterized by lactic acidemia, developmental delay, and hypotonia. Other features are feeding difficulties, growth failure, microcephaly, hyperammonemia, seizures, hypertrophic cardiomyopathy, elevated liver transaminases, recurrent infections, variable distinctive facial features, white matter abnormalities and cerebral atrophy found in neuroimaging, combined deficiencies of multiple electron transport complexes, and mtDNA depletion. Since its initial description in 2013, 36 different pathogenic variants in FBXL4 were reported in 50 affected individuals. In this report, we present 37 additional affected individuals and 11 previously unreported pathogenic variants. We summarize the clinical features of all 87 individuals with FBXL4-related mtDNA maintenance defect, review FBXL4 structure and function, map the 47 pathogenic variants onto the gene structure to assess the variants distribution, and investigate the genotype-phenotype correlation. Finally, we provide future directions to understand the disease mechanism and identify treatment strategies. This article is protected by copyright. All rights reserved.
View details for PubMedID 28940506
De novo mutations on maternal alleles in two patients with neuronopathic Gaucher disease
ACADEMIC PRESS INC ELSEVIER SCIENCE. 2015: 359–60
View details for Web of Science ID 000351191800099
GAUCHER DISEASE AND LANGERHANS CELL HISTIOCYTOSIS
ACADEMIC PRESS INC ELSEVIER SCIENCE. 2014: 267–68
View details for Web of Science ID 000332500200085
Germline loss-of-function mutations in LZTR1 predispose to an inherited disorder of multiple schwannomas
2014; 46 (2): 182-?
Constitutional SMARCB1 mutations at 22q11.23 have been found in ∼50% of familial and <10% of sporadic schwannomatosis cases. We sequenced highly conserved regions along 22q from eight individuals with schwannomatosis whose schwannomas involved somatic loss of one copy of 22q, encompassing SMARCB1 and NF2, with a different somatic mutation of the other NF2 allele in every schwannoma but no mutation of the remaining SMARCB1 allele in blood and tumor samples. LZTR1 germline mutations were identified in seven of the eight cases. LZTR1 sequencing in 12 further cases with the same molecular signature identified 9 additional germline mutations. Loss of heterozygosity with retention of an LZTR1 mutation was present in all 25 schwannomas studied. Mutations segregated with disease in all available affected first-degree relatives, although four asymptomatic parents also carried an LZTR1 mutation. Our findings identify LZTR1 as a gene predisposing to an autosomal dominant inherited disorder of multiple schwannomas in ∼80% of 22q-related schwannomatosis cases lacking mutation in SMARCB1.
View details for DOI 10.1038/ng.2855
View details for Web of Science ID 000331208300016
View details for PubMedID 24362817
View details for PubMedCentralID PMC4352302
PREGNANCY OUTCOMES IN MAPLE SYRUP URINE DISEASE
LIPPINCOTT WILLIAMS & WILKINS. 2014: 199
View details for Web of Science ID 000336284900197
Teaching NeuroImages: Infant with glutaric aciduria type 1 presenting with infantile spasms and hypsarrhythmia
2013; 81 (24): E182–E183
A 7-month-old boy with glutaric aciduria type 1 (GA1) presented with 1 week of clustered flexor spasms. Examination revealed mild axial hypotonia without encephalopathy. Video-EEG monitoring revealed hypsarrhythmia and infantile spasms (figure, A). MRI showed acute basal ganglia injury (figure, B). After 3 weeks of prednisolone treatment, 5-month follow-up showed continued resolution of hypsarrhythmia and spasms.
View details for DOI 10.1212/01.wnl.0000437291.75075.53
View details for Web of Science ID 000330772300002
View details for PubMedID 24323445
View details for PubMedCentralID PMC3863345
- Homozygosity for a FBN1 missense mutation causes a severe Marfan syndrome phenotype CLINICAL GENETICS 2013; 84 (4): 392-393
The phenotype of Floating-Harbor syndrome: clinical characterization of 52 individuals with mutations in exon 34 of SRCAP
ORPHANET JOURNAL OF RARE DISEASES
Floating-Harbor syndrome (FHS) is a rare condition characterized by short stature, delays in expressive language, and a distinctive facial appearance. Recently, heterozygous truncating mutations in SRCAP were determined to be disease-causing. With the availability of a DNA based confirmatory test, we set forth to define the clinical features of this syndrome.Clinical information on fifty-two individuals with SRCAP mutations was collected using standardized questionnaires. Twenty-four males and twenty-eight females were studied with ages ranging from 2 to 52 years. The facial phenotype and expressive language impairments were defining features within the group. Height measurements were typically between minus two and minus four standard deviations, with occipitofrontal circumferences usually within the average range. Thirty-three of the subjects (63%) had at least one major anomaly requiring medical intervention. We did not observe any specific phenotype-genotype correlations.This large cohort of individuals with molecularly confirmed FHS has allowed us to better delineate the clinical features of this rare but classic genetic syndrome, thereby facilitating the development of management protocols.
View details for DOI 10.1186/1750-1172-8-63
View details for Web of Science ID 000319314600001
View details for PubMedID 23621943
View details for PubMedCentralID PMC3659005