Targeted broad-based genetic testing by next-generation sequencing informs diagnosis and facilitates management in patients with kidney diseases.

BACKGROUND: The clinical diagnosis of genetic renal diseases may be limited by the overlapping spectrum of manifestations between diseases or by the advancement of disease where clues to the original process are absent. The objective of this study was to determine whether genetic testing informs diagnosis and facilitates management of kidney disease patients. METHODS: We developed a comprehensive genetic testing panel (KidneySeq) to evaluate patients with various phenotypes including cystic diseases, congenital anomalies of the kidney and urinary tract (CAKUT), tubulointerstitial diseases, transport disorders and glomerular diseases. We evaluated this panel in 127 consecutive patients ranging in age from newborns to 81 years who had samples sent in for genetic testing. RESULTS: The performance of the sequencing pipeline for single-nucleotide variants was validated using CEPH (Centre de'Etude du Polymorphism) controls and for indels using Genome-in-a-Bottle. To test the reliability of the copy number variant (CNV) analysis, positive samples were re-sequenced and analyzed. For patient samples, a multidisciplinary review board interpreted genetic results in the context of clinical data. A genetic diagnosis was made in 54 (43%) patients and ranged from 54% for CAKUT, 53% for ciliopathies/tubulointerstitial diseases, 45% for transport disorders to 33% for glomerulopathies. Pathogenic and likely pathogenic variants included 46% missense, 11% nonsense, 6% splice site variants, 23% insertion-deletions and 14% CNVs. In 13 cases, the genetic result changed the clinical diagnosis. CONCLUSION: Broad genetic testing should be considered in the evaluation of renal patients as it complements other tests and provides insight into the underlying disease and its management.

DNM1 encephalopathy: A new disease of vesicle fission.

OBJECTIVE: To evaluate the phenotypic spectrum caused by mutations in dynamin 1 (DNM1), encoding the presynaptic protein DNM1, and to investigate possible genotype-phenotype correlations and predicted functional consequences based on structural modeling. METHODS: We reviewed phenotypic data of 21 patients (7 previously published) with DNM1 mutations. We compared mutation data to known functional data and undertook biomolecular modeling to assess the effect of the mutations on protein function. RESULTS: We identified 19 patients with de novo mutations in DNM1 and a sibling pair who had an inherited mutation from a mosaic parent. Seven patients (33.3%) carried the recurrent p.Arg237Trp mutation. A common phenotype emerged that included severe to profound intellectual disability and muscular hypotonia in all patients and an epilepsy characterized by infantile spasms in 16 of 21 patients, frequently evolving into Lennox-Gastaut syndrome. Two patients had profound global developmental delay without seizures. In addition, we describe a single patient with normal development before the onset of a catastrophic epilepsy, consistent with febrile infection-related epilepsy syndrome at 4 years. All mutations cluster within the GTPase or middle domains, and structural modeling and existing functional data suggest a dominant-negative effect on DMN1 function. CONCLUSIONS: The phenotypic spectrum of DNM1-related encephalopathy is relatively homogeneous, in contrast to many other genetic epilepsies. Up to one-third of patients carry the recurrent p.Arg237Trp variant, which is now one of the most common recurrent variants in epileptic encephalopathies identified to date. Given the predicted dominant-negative mechanism of this mutation, this variant presents a prime target for therapeutic intervention.

Collaborative Counseling Considerations for Pharmacogenomic Tests.

Increased use of pharmacogenomic (PGx) testing in the clinical setting has revealed a number of challenges to providing this service. PGx is an important component of precision medicine that brings together the fields of genetics and clinical pharmacology. A model that incorporates a multidisciplinary approach to implementation and information delivery may be the most beneficial to patients and providers. In this review, translational considerations in the provision of PGx testing and counseling services are described. Specifically, we report on the selection of PGx tests, the provision of patient education and counseling, and examples of PGx service delivery models that incorporate counseling by pharmacists and genetic counselors. Examples of ancillary risks associated with PGx testing, testing of children, and familial implications of testing are reviewed. Through multispecialty partnerships, including genetic counselors and pharmacists, implementation obstacles to PGx testing can be overcome to provide quality precision medicine to patients.

Reducing the Cost of the Diagnostic Odyssey in Early Onset Epileptic Encephalopathies.

Whole exome sequencing (WES) has revolutionized the way we think about and diagnose epileptic encephalopathies. Multiple recent review articles discuss the benefits of WES and suggest various algorithms to follow for determining the etiology of epileptic encephalopathies. Incorporation of WES in these algorithms is leading to the discovery of new genetic diagnoses of early onset epileptic encephalopathies (EOEEs) at a rapid rate; however, WES is not yet a universally utilized diagnostic tool. Clinical WES may be underutilized due to provider discomfort in ordering the test or perceived costliness. At our hospital WES is not routinely performed for patients with EOEE due to limited insurance reimbursement. In fact for any patient with noncommercial insurance (Medicaid) the institution does not allow sending out WES as this is not "established"/"proven to be highly useful and cost effective"/"approved test" in patients with epilepsy. Recently, we performed WES on four patients from three families and identified novel mutations in known epilepsy genes in all four cases. These patients had State Medicaid as their insurance carrier and were followed up for several years for EOEE while being worked up using the traditional/approved testing methods. Following a recently proposed diagnostic pathway, we analyzed the cost savings (US dollars) that could be accrued if WES was performed earlier in the diagnostic odyssey. This is the first publication that addresses the dollar cost of traditional testing in EOEE as performed in these four cases versus WES and the potential cost savings.

Ketogenic diet - A novel treatment for early epileptic encephalopathy due to PIGA deficiency.

We describe the presentation and workup of two brothers with early-onset epileptic encephalopathy who became seizure-free on a ketogenic diet. Extensive testing culminated in whole exome sequencing, which led to the diagnosis of phosphatidyl inositol glycan biosynthesis class A protein (PIGA) deficiency. This familial case highlights the importance of genetic testing for early-onset epileptic encephalopathies and underscores the potential value of a ketogenic diet in the treatment of this condition.

Comprehensive genetic testing in the clinical evaluation of 1119 patients with hearing loss.

Hearing loss is the most common sensory deficit in humans, affecting 1 in 500 newborns. Due to its genetic heterogeneity, comprehensive diagnostic testing has not previously been completed in a large multiethnic cohort. To determine the aggregate contribution inheritance makes to non-syndromic hearing loss, we performed comprehensive clinical genetic testing with targeted genomic enrichment and massively parallel sequencing on 1119 sequentially accrued patients. No patient was excluded based on phenotype, inheritance or previous testing. Testing resulted in identification of the underlying genetic cause for hearing loss in 440 patients (39%). Pathogenic variants were found in 49 genes and included missense variants (49%), large copy number changes (18%), small insertions and deletions (18%), nonsense variants (8%), splice-site alterations (6%), and promoter variants (<1%). The diagnostic rate varied considerably based on phenotype and was highest for patients with a positive family history of hearing loss or when the loss was congenital and symmetric. The spectrum of implicated genes showed wide ethnic variability. These findings support the more efficient utilization of medical resources through the development of evidence-based algorithms for the diagnosis of hearing loss.

Mutations in apoptosis-inducing factor cause X-linked recessive auditory neuropathy spectrum disorder.

BACKGROUND: Auditory neuropathy spectrum disorder (ANSD) is a form of hearing loss in which auditory signal transmission from the inner ear to the auditory nerve and brain stem is distorted, giving rise to speech perception difficulties beyond that expected for the observed degree of hearing loss. For many cases of ANSD, the underlying molecular pathology and the site of lesion remain unclear. The X-linked form of the condition, AUNX1, has been mapped to Xq23-q27.3, although the causative gene has yet to be identified. METHODS: We performed whole-exome sequencing on DNA samples from the AUNX1 family and another small phenotypically similar but unrelated ANSD family. RESULTS: We identified two missense mutations in AIFM1 in these families: c.1352G>A (p.R451Q) in the AUNX1 family and c.1030C>T (p.L344F) in the second ANSD family. Mutation screening in a large cohort of 3 additional unrelated families and 93 sporadic cases with ANSD identified 9 more missense mutations in AIFM1. Bioinformatics analysis and expression studies support this gene as being causative of ANSD. CONCLUSIONS: Variants in AIFM1 gene are a common cause of familial and sporadic ANSD and provide insight into the expanded spectrum of AIFM1-associated diseases. The finding of cochlear nerve hypoplasia in some patients was AIFM1-related ANSD implies that MRI may be of value in localising the site of lesion and suggests that cochlea implantation in these patients may have limited success.

Functional variants in NOS1 and NOS2A are not associated with progressive hearing loss in Ménière's disease in a European Caucasian population.

Hearing loss in Ménière's disease (MD) is associated with loss of spiral ganglion neurons and hair cells. In a guinea pig model of endolymphatic hydrops, nitric oxide synthases (NOS) and oxidative stress mediate loss of spiral ganglion neurons. To test the hypothesis that functional variants of NOS1 and NOS2A are associated with MD, we genotyped three functional variants of NOS1 (rs41279104, rs2682826, and a cytosine-adenosine microsatellite repeat in exon 1f) and the CCTTT repeat in the promoter of NOS2A gene (rs3833912) in two independent MD sets (273 patients in total) and 550 controls. A third cohort of American patients was genotyped as replication cohort for the CCTTT repeat. Neither allele nor genotype frequencies of rs41279104 and rs2682826 were associated with MD, although longer alleles of the cytosine-adenosine microsatellite repeat were marginally significant (corrected p = 0.05) in the Mediterranean cohort but not in a second Galicia cohort. Shorter numbers of the CCTTT repeat in NOS2A were significantly more frequent in Galicia controls (OR = 0.37 [CI, 0.18-0.76], corrected p = 0.04), but this finding could not be replicated in Mediterranean or American case-control populations. Meta-analysis did not support an association between CCTTT repeats and risk for MD. Severe hearing loss (>75 dB) was also not associated with any functional variants studied. Functional variants of NOS1 and NOS2A do not confer susceptibility for MD.

Polymorphisms in KCNE1 or KCNE3 are not associated with Ménière disease in the Caucasian population.

Ménière disease (MD) is a complex disorder of unknown etiology characterized by the symptom triad of vertigo, sensorineural hearing loss, and tinnitus. Its reported incidence is 1-2 per 1,000 in Caucasians and 0.03-0.37 per 1,000 in Japanese. Doi et al. [Doi et al. (2005); ORL J Otorhinolaryngol Relat Spec 67:289-293] recently reported that two single nucleotide polymorphisms (SNPs) in KCNE1 and KCNE3 are associated with MD in Japanese subjects. Consistent with this possibility, these two genes encode potassium channels that are expressed in the stria vascularis and endolymphatic sac, respectively, and their role in ion transport suggests that they may be important in inner ear homeostasis. To establish whether a similar association exists in the Caucasian MD population, we sequenced the coding regions and exon-intron boundaries of both genes in 180 Caucasian persons with MD and 180 matched Caucasian controls. Neither of the two reported SNPs was significantly associated with MD when compared to the Caucasian controls (KCNE1, P = 0.55; KCNE3, P = 0.870). Comparison of allele frequencies between the Japanese MD population and our study population revealed no significant difference between groups (KCNE1, P = 0.90; KCNE3, P = 0.862), suggesting that the significant differences reported in the Japanese study arose from their control population. Six additional SNPs in both KCNE1 and KCNE3 were genotyped and none was associated with MD. Population stratification within our MD and Caucasian control population was excluded. Our data show that SNPs in KCNE1 and KCNE3 are not associated with MD in Caucasians.

Gene expression profiling analysis of the inner ear.

Recent developments in molecular genetics, including progress in the human genome project, have allowed identification of genes at an unprecedented rate. To date gene expression profiling studies have focused on identifying transcripts that are specifically or preferentially enriched within the inner ear on the assumption that they are more likely to be important for auditory and vestibular function. It is now apparent that some genes preferentially expressed in the cochleo-vestibular system are not crucial for hearing or balance or their functions are compensated for by other genes. In addition, transcripts expressed at low abundance in the inner ear are generally under-represented in gene profiling studies. In this review, we highlight the limitations of current gene expression profiling strategies as a discovery tool for genes involved in cochleo-vestibular development and function. We argue that expression profiling based on hierarchical clustering of transcripts by gene ontology, combined with tissue enrichment data, is more effective for inner ear gene discovery. This approach also provides a framework to assist and direct the functional characterization of gene products.

Deletion of and novel missense mutation in POU3F4 in 2 families segregating X-linked nonsyndromic deafness.

OBJECTIVE: To analyze the physical manifestations and genetic features of 2 families segregating X-linked deafness, which is most commonly reported to be caused by mutations of the POU domain gene POU3F4 at the DFN3 locus. DESIGN: Computed tomographic study of the temporal bone in probands from each family, followed by mutation screening and deletion mapping of POU3F4 in family members. SETTING: Two midwestern genetics clinics. PARTICIPANTS: Two families with X-linked deafness. MAIN OUTCOME MEASURES: Anomalies of the inner ear in the probands; results of gene mapping and severity and effects of hearing loss in the family members. RESULTS: In the first family, a large deletion was identified that includes POU3F4 and extends upstream approximately 530 kilobases; in the second family, a novel serine-to-leucine (S228L) amino acid mutation was identified in the POU-specific domain of POU3F4. Both the deletion and the missense mutation segregate with the clinical phenotype and are causally related to the deafness in these families. CONCLUSIONS: Deafness related to the POU3F4 gene is associated with dilation of the internal auditory canal and a spectrum of other temporal bone anomalies that range in severity from mild to severe dysplasia of the cochlea and semicircular canals. The consequence of these anomalies is a congenital mixed hearing loss, the sensorineural component of which progresses over time. Affected males can also present with vestibular dysfunction that is associated with delayed developmental motor milestones. Intrafamilial variability occurs.