Biallelic and monoallelic variants in PLXNA1 are implicated in a novel neurodevelopmental disorder with variable cerebral and eye anomalies.

PURPOSE: To investigate the effect of PLXNA1 variants on the phenotype of patients with autosomal dominant and recessive inheritance patterns and to functionally characterize the zebrafish homologs plxna1a and plxna1b during development. METHODS: We assembled ten patients from seven families with biallelic or de novo PLXNA1 variants. We describe genotype-phenotype correlations, investigated the variants by structural modeling, and used Morpholino knockdown experiments in zebrafish to characterize the embryonic role of plxna1a and plxna1b. RESULTS: Shared phenotypic features among patients include global developmental delay (9/10), brain anomalies (6/10), and eye anomalies (7/10). Notably, seizures were predominantly reported in patients with monoallelic variants. Structural modeling of missense variants in PLXNA1 suggests distortion in the native protein. Our zebrafish studies enforce an embryonic role of plxna1a and plxna1b in the development of the central nervous system and the eye. CONCLUSION: We propose that different biallelic and monoallelic variants in PLXNA1 result in a novel neurodevelopmental syndrome mainly comprising developmental delay, brain, and eye anomalies. We hypothesize that biallelic variants in the extracellular Plexin-A1 domains lead to impaired dimerization or lack of receptor molecules, whereas monoallelic variants in the intracellular Plexin-A1 domains might impair downstream signaling through a dominant-negative effect.

Autozygome and high throughput confirmation of disease genes candidacy.

PURPOSE: Establishing links between Mendelian phenotypes and genes enables the proper interpretation of variants therein. Autozygome, a rich source of homozygous variants, has been successfully utilized for the high throughput identification of novel autosomal recessive disease genes. Here, we highlight the utility of the autozygome for the high throughput confirmation of previously published tentative links to diseases. METHODS: Autozygome and exome analysis of patients with suspected Mendelian phenotypes. All variants were classified according to the American College of Medical Genetics and Genomics guidelines. RESULTS: We highlight 30 published candidate genes (ACTL6B, ADAM22, AGTPBP1, APC, C12orf4, C3orf17 (NEPRO), CENPF, CNPY3, COL27A1, DMBX1, FUT8, GOLGA2, KIAA0556, LENG8, MCIDAS, MTMR9, MYH11, QRSL1, RUBCN, SLC25A42, SLC9A1, TBXT, TFG, THUMPD1, TRAF3IP2, UFC1, UFM1, WDR81, XRCC2, ZAK) in which we identified homozygous likely deleterious variants in patients with compatible phenotypes. We also identified homozygous likely deleterious variants in 18 published candidate genes (ABCA2, ARL6IP1, ATP8A2, CDK9, CNKSR1, DGAT1, DMXL2, GEMIN4, HCN2, HCRT, MYO9A, PARS2, PLOD3, PREPL, SCLT1, STX3, TXNRD2, WIPI2) although the associated phenotypes are sufficiently different from the original reports that they represent phenotypic expansion or potentially distinct allelic disorders. CONCLUSIONS: Our results should facilitate the timely relabeling of these candidate disease genes in relevant databases to improve the yield of clinical genomic sequencing.

Lethal digenic mutations in the K+ channels Kir4.1 (KCNJ10) and SLACK (KCNT1) associated with severe-disabling seizures and neurodevelopmental delay.

A 2-yr-old boy presented profound developmental delay, failure to thrive, ataxia, hypotonia, and tonic-clonic seizures that caused the death of the patient. Targeted and whole exome sequencing revealed two heterozygous missense variants: a novel mutation in the KCNJ10 gene that encodes for the inward-rectifying K+ channel Kir4.1 and another previously characterized mutation in KCNT1 that encodes for the Na+-activated K+ channel known as Slo2.2 or SLACK. The objectives of this study were to perform the clinical and genetic characterization of the proband and his family and to examine the functional consequence of the Kir4.1 mutation. The mutant and wild-type KCNJ10 constructs were generated and heterologously expressed in Xenopus laevis oocytes, and whole cell K+ currents were measured using the two-electrode voltage-clamp technique. The KCNJ10 mutation c.652C>T resulted in a p.L218F substitution at a highly conserved residue site. Wild-type KCNJ10 expression yielded robust Kir current, whereas currents from oocytes expressing the mutation were reduced, remarkably. Western Blot analysis revealed reduced protein expression by the mutation. Kir5.1 subunits display selective heteromultimerization with Kir4.1 constituting channels with unique kinetics. The effect of the mutation on Kir4.1/5.1 channel activity was twofold: a reduction in current amplitudes and an increase in the pH-dependent inhibition. We thus report a novel loss-of-function mutation in Kir4.1 found in a patient with a coexisting mutation in SLACK channels that results in a fatal disease.NEW & NOTEWORTHY We present and characterize a novel mutation in KCNJ10 Unlike previously reported EAST/SeSAME patients, our patient was heterozygous, and contrary to previous studies, mimicking the heterozygous state by coexpression resulted in loss of channel function. We report in the same patient co-occurrence of a KCNT1 mutation resulting in a more severe phenotype. This study provides new insights into the phenotypic spectrum and to the genotype-phenotype correlations associated with EAST/SeSAME and MMFSI.

The landscape of genetic diseases in Saudi Arabia based on the first 1000 diagnostic panels and exomes.

In this study, we report the experience of the only reference clinical next-generation sequencing lab in Saudi Arabia with the first 1000 families who span a wide-range of suspected Mendelian phenotypes. A total of 1019 tests were performed in the period of March 2016-December 2016 comprising 972 solo (index only), 14 duo (parents or affected siblings only), and 33 trio (index and parents). Multigene panels accounted for 672 tests, while whole exome sequencing (WES) represented the remaining 347 tests. Pathogenic or likely pathogenic variants that explain the clinical indications were identified in 34% (27% in panels and 43% in exomes), spanning 279 genes and including 165 novel variants. While recessive mutations dominated the landscape of solved cases (71% of mutations, and 97% of which are homozygous), a substantial minority (27%) were solved on the basis of dominant mutations. The highly consanguineous nature of the study population also facilitated homozygosity for many private mutations (only 32.5% of the recessive mutations are founder), as well as the first instances of recessive inheritance of previously assumed strictly dominant disorders (involving ITPR1, VAMP1, MCTP2, and TBP). Surprisingly, however, dual molecular diagnosis was only observed in 1.5% of cases. Finally, we have encountered candidate variants in 75 genes (ABHD6, ACY3, ADGRB2, ADGRG7, AGTPBP1, AHNAK2, AKAP6, ASB3, ATXN1L, C17orf62, CABP1, CCDC186, CCP110, CLSTN2, CNTN3, CNTN5, CTNNA2, CWC22, DMAP1, DMKN, DMXL1, DSCAM, DVL2, ECI1, EP400, EPB41L5, FBXL22, GAP43, GEMIN7, GIT1, GRIK4, GRSF1, GTRP1, HID1, IFNL1, KCNC4, LRRC52, MAP7D3, MCTP2, MED26, MPP7, MRPS35, MTDH, MTMR9, NECAP2, NPAT, NRAP, PAX7, PCNX, PLCH2, PLEKHF1, PTPN12, QKI, RILPL2, RIMKLA, RIMS2, RNF213, ROBO1, SEC16A, SIAH1, SIRT2, SLAIN2, SLC22A20, SMDT1, SRRT, SSTR1, ST20, SYT9, TSPAN6, UBR4, VAMP4, VPS36, WDR59, WDYHV1, and WHSC1) not previously linked to human phenotypes and these are presented to accelerate post-publication matchmaking. Two of these genes were independently mutated in more than one family with similar phenotypes, which substantiates their link to human disease (AKAP6 in intellectual disability and UBR4 in early dementia). If the novel candidate disease genes in this cohort are independently confirmed, the yield of WES will have increased to 83%, which suggests that most "negative" clinical exome tests are unsolved due to interpretation rather than technical limitations.

Severe hypoglycemic seizures in a child receiving 6-mercaptopurine.

A 4-year-old boy with acute lymphoblastic leukemia who was receiving 6-mercaptopurine during the maintenance chemotherapy experienced prolonged generalized tonic nocturnal seizures because of severe hypoglycemia after his evening dose by a 12-hour period of fasting. Investigations ruled out all causes of these seizures other than the 6-mercaptopurine-induced severe hypoglycemia.

Phenotypic Variability of MEGF10 Variants Causing Congenital Myopathy: Report of Two Unrelated Patients from a Highly Consanguineous Population.

Congenital myopathies are rare neuromuscular hereditary disorders that manifest at birth or during infancy and usually appear with muscle weakness and hypotonia. One of such disorders, early-onset myopathy, areflexia, respiratory distress, and dysphagia (EMARDD, OMIM: 614399, MIM: 612453), is a rare autosomal recessive disorder caused by biallelic mutations (at homozygous or compound heterozygous status) in MEGF10 (multiple epidermal growth factor-like domains protein family). Here, we report two unrelated patients, who were born to consanguineous parents, having two novel MEGF10 deleterious variants. Interestingly, the presence of MEGF10 associated EMARDD has not been reported in Saudi Arabia, a highly consanguineous population. Moreover, both variants lead to a different phenotypic onset of mild and severe types. Our work expands phenotypic features of the disease and provides an opportunity for genetic counseling to the inflicted families.

Tuberous Sclerosis Complex: Clinical Spectrum and Epilepsy: A Retrospective Chart Review Study.

Tuberous sclerosis complex (TSC) is an autosomal dominant genetic neurocutaneous disorder, with heterogeneous manifestations. We aimed to review the clinical presentation of TSC and its association with epilepsy among Saudi population. This was a retrospective chart review study of 88 patients diagnosed with TSC with or without epilepsy. In 38.6% of patients, symptoms began before 1 year of age. The most frequent initial manifestations of TSC were new onset of seizures (68.2%), skin manifestations (46.6%) and development delay (23.9%). During the evolution of the disease 65.9% had epilepsy, 17% facial angiofibromas, 13.6% Shagreen patch, 18.2% heart rhabdomyomas and 12.5% retinal hamartomas. The genetic study for TSC diagnosis was done for 44 patients, 42 (95,4%) of them were genetically confirmed, for whom 13 patients had TSC1 mutation (29.5%), 29 patients were carrying TSC2 gene mutation (65.9%), Genetic test for TSC 1 and TSC 2 were negative for 2 patients (4.5%) despite positive gene mutation in their relative with TSC. The most common manifestations were central nervous system (predominantly epilepsy) and dermatological manifestations. Most of the patients develop epilepsy with multiple seizure types. TSC 2 mutation is more common than TSC 1 mutation.

Acute disseminated encephalomyelitis and thrombocytopenia following Epstein-Barr virus infection.

Epstein-Barr Virus (EBV) causes a broad spectrum of disease in humans with several clinical syndromes and is ubiquitous, infecting more than 95% of the world's population. Central Nervous System (CNS) disease alone associated with Epstein-Barr virus rarely occurs in previously healthy individuals. Systemic viral illness in children and complications are rare, but may occur. In few cases, it is associated with a variety of CNS and hematological complications like acute disseminated encephalomyelitis, transverse myelitis, neuropsychiatric syndrome, GBS, autoimmune thrombocytopenia and hemolytic anemia and they usually respond to immunotherapy. We report previously healthy boy, who presented with left sided weakness, headache and thrombocytopenia following EBV infection. The thrombocytopenia was resistant to intravenous immunoglobulin and methylprednisolone but responded well to Rituximab.

Anti-N-methyl-D-aspartate (NMDA) receptor encephalitis in a young Lebanese girl.

Anti-N-methyl-D-aspartate (NMDA) receptor encephalitis is a recently recognized autoimmune neurologic disorder that presents with severe neuropsychiatric symptoms in previously healthy children. A 4-year-old Lebanese girl presented with new-onset behavioral changes, orofacial dyskinesias, fluctuation in consciousness, inability to walk, and mutism. Antibodies directed against NMDA receptors were detected in the patient's serum and cerebrospinal fluid. Prompt treatment with a single course of intravenous immunoglobulin resulted in early complete recovery. This is the first case report of a Middle Eastern child affected with this condition.

Paroxysmal autonomic instability with dystonia after pneumococcal meningoencephalitis.

Streptococcus pneumoniae is a common cause of bacterial meningitis, frequently resulting in severe neurological impairment. A seven-month-old child presenting with Streptococcus pneumoniae meningoencephalitis developed right basal ganglia and hypothalamic infarctions. Daily episodes of agitation, hypertension, tachycardia, diaphoresis, hyperthermia, and decerebrate posturing were observed. The diagnosis of paroxysmal autonomic instability with dystonia was established. The patient responded to clonidine, baclofen, and benzodiazepines. Although this entity has been reported in association with traumatic brain injury, and as a sequel to some nervous system infections, this is the first case, to our knowledge, associated with pneumococcal meningoencephalitis.

Cardiac involvement in nonketotic hyperglycinemia.

Nonketotic hyperglycinemia is an autosomal recessive disorder of glycine metabolism characterized by the accumulation of glycine in the serum and cerebrospinal fluid with elevated cerebrospinal fluid to serum glycine ratio. The disease primarily affects the central nervous system, and has not been previously associated with myocardial involvement. In this article, the authors report an infant with nonketotic hyperglycinemia, who was found to have progressive left ventricular hypertrophy and dysfunction. His older sibling, who had a similar neurologic presentation, died of dilated cardiomyopathy as stated by the parents. The authors speculate that glycine may have a role in the development of cardiac dysfunction. The incidence of cardiac involvement may be under-diagnosed. They suggest the need for a cardiac evaluation in confirmed cases of nonketotic hyperglycinemia.

Severe cerebral vaso-occlusive disease in macrophage activation syndrome.

A 14-year-old girl was diagnosed with macrophage activation syndrome, based on clinical presentation, laboratory tests, and bone marrow aspirate findings. She developed severe central nervous system involvement in the form of seizure disorder and severe diffuse occlusive cerebral vasculopathy, with extensive collateral circulation consistent with moyamoya disease. To our knowledge, this description is the first of these findings in association with macrophage activation syndrome.