Clinical and Molecular Characteristics of Neuronal Ceroid Lipofuscinosis in Saudi Arabia

BACKGROUND

Neuronal ceroid lipofuscinoses (NCLs) represent a heterogeneous group of inherited metabolic lysosomal disorders characterized by neurodegeneration. This study sought to describe the clinical and molecular characteristics of NCLs in Saudi Arabia and determine the most common types in that population.

METHODS

A retrospective review of electronic medical records was conducted for 63 patients with NCL (55 families) from six tertiary and referral centers in Saudi Arabia between 2008 and 2022. Clinical, radiological, and neurophysiological data as well as genetic diagnoses were reviewed.

RESULTS

CLN6 was the predominant type, accounting for 45% of cases in 25 families. The most common initial symptoms were speech delay (53%), cognitive decline (50%) and/or gait abnormalities (48%), and seizure (40%). Behavioral symptomatology was observed in 20%, whereas visual impairment was less frequently (9.3%) encountered. Diffuse cerebral and cerebellar atrophy was the predominant finding on brain magnetic resonance imaging. Electroencephalography generally revealed background slowing in all patients with generalized epileptiform discharges in 60%. The most common genotype detected was the p.Ser265del variant found in 36% (20 of 55 families). The most rapidly progressive subtypes were CLN2 and CLN6. Two patients with each died at age five years. The earliest age at which a patient was nonambulatory was two years in a patient with CLN14.

CONCLUSIONS

This is the largest molecularly confirmed NCL cohort study from Saudi Arabia. Characterizing the natural history of specific NLC types can increase understanding of the underlying pathophysiology and distinctive genotype-phenotype characteristics, facilitating early diagnosis and treatment initiation as well as genetic counseling for families.

Diagnostic comparison between cord blood and filter paper for the screening of congenital hypothyroidism

Background

Cord‐blood and heel‐prick TSH levels are essential in diagnosing and preventing the serious complications of congenital hypothyroidism, which mainly include intellectual disability. The study aimed to compare between cord‐blood and heel‐prick TSH sensitivity and specificity in detecting congenital hypothyroidism (CH) among newborn screened babies.

Method

The study included 21,012 newborn screened babies for congenital hypothyroidism starting from September 2013 until March 2019. Both cord‐blood and heel‐prick TSH were collected from each newborn. Heel prick and cord‐blood TSH cutoff values of >21 μU/ml and >30 mIU/L respectively were considered positive.

Results

Out of the total screened newborns, 12 were confirmed for having primary congenital hypothyroidism. Nine cases were positive for cord‐blood TSH (Sensitivity 75%, specificity 99.9%, and a recall rate of 0.004%), while 139 cases were positive for heel‐prick blood TSH (Sensitivity of 100%, specificity of 99.3%, and a recall rate of 0.60%).

Conclusion

For the screening of CH, heel prick is considered a superior method, but cord blood remains a practical option due to its cost‐effectiveness, immediate action, and lower recall rate. Therefore, whenever recall is difficult and/or early discharge is the practice, cord blood is an alternative method to heel prick but not with cases of prematurity.

Insight into ALKBH8-related intellectual developmental disability based on the first pathogenic missense variant

ALKBH8 is a methyltransferase that modifies tRNAs by methylating the anticodon wobble uridine residue. The syndrome of ALKBH8-related intellectual developmental disability (MRT71) has thus far been reported solely in the context of homozygous truncating variants that cluster in the last exon. This raises interesting questions about the disease mechanism, because these variants are predicted to escape nonsense mediated decay and yet they appear to be loss of function. Furthermore, the limited class of reported variants complicates the future interpretation of missense variants in ALKBH8. Here, we report a consanguineous family in which two children with MRT71-compatible phenotype are homozygous for a novel missense variant in the methyltransferase domain. We confirm the pathogenicity of this variant by demonstrating complete absence of ALKBH8-dependent modifications in patient cells. Targeted proteomics analysis of ALKBH8 indicates that the variant does not lead to loss of ALKBH8 protein expression. This report adds to the clinical delineation of MRT71, confirms loss of function of ALKBH8 as the disease mechanism and expands the repertoire of its molecular lesions.

The phenotypic spectrum of dihydrolipoamide dehydrogenase deficiency in Saudi Arabia

Background

Dihydrolipoamide dehydrogenase deficiency (DLDD) is a rare metabolic disorder inherited in an autosomal recessive manner. This heterogeneous disease has a variable clinical presentation, onset, and biochemical markers.

Materials and methods

We retrospectively reviewed the clinical and molecular diagnosis of eight cases with DLDD from four referral centers in Saudi Arabia.

Results

Remarkably, we found hepatic involvement ranging from acute hepatic failure to chronic hepatitis in five patients. In addition, neurological disorders in the form of seizures, developmental delay, ataxia, hypotonia and psychomotor symptoms were found in five patients, two of them with a combination of hepatic and neurological symptoms. In addition, only one patient had recurrent episodes of hypoglycemia. While most patients had the hepatic form of homozygous variant c.685G > T in the DLD gene, one patient was found to have a novel variant c.623C > T that had neurological and hepatic symptoms.

Conclusions

We describe the largest reported DLDD cohort in the Saudi population. Clinical, biochemical, radiological, and molecular characterization was reviewed and no clear genotype-phenotype correlation was found in this cohort.

NBAS Variants Are Associated with Quantitative and Qualitative NK and B Cell Deficiency

PURPOSE

Biallelic pathogenic NBAS variants manifest as a multisystem disorder with heterogeneous clinical phenotypes such as recurrent acute liver failure, growth retardation, and susceptibility to infections. This study explores how NBAS-associated disease affects cells of the innate and adaptive immune system.

METHODS

Clinical and laboratory parameters were combined with functional multi-parametric immunophenotyping methods in fifteen NBAS-deficient patients to discover possible alterations in their immune system.

RESULTS

Our study revealed reduced absolute numbers of mature CD56dim natural killer (NK) cells. Notably, the residual NK cell population in NBAS-deficient patients exerted a lower potential for activation and degranulation in response to K562 target cells, suggesting an NK cell-intrinsic role for NBAS in the release of cytotoxic granules. NBAS-deficient NK cell activation and degranulation was normalized upon pre-activation by IL-2 in vitro, suggesting that functional impairment was reversible. In addition, we observed a reduced number of naïve B cells in the peripheral blood associated with hypogammaglobulinemia.

CONCLUSION

In summary, we demonstrate that pathogenic biallelic variants in NBAS are associated with dysfunctional NK cells as well as impaired adaptive humoral immunity.

YIF1B mutations cause a post-natal neurodevelopmental syndrome associated with Golgi and primary cilium alterations

Human post-natal neurodevelopmental delay is often associated with cerebral alterations that can lead, by themselves or associated with peripheral deficits, to premature death. Here, we report the clinical features of 10 patients from six independent families with mutations in the autosomal YIF1B gene encoding a ubiquitous protein involved in anterograde traffic from the endoplasmic reticulum to the cell membrane, and in Golgi apparatus morphology. The patients displayed global developmental delay, motor delay, visual deficits with brain MRI evidence of ventricle enlargement, myelination alterations and cerebellar atrophy. A similar profile was observed in the Yif1b knockout (KO) mouse model developed to identify the cellular alterations involved in the clinical defects. In the CNS, mice lacking Yif1b displayed neuronal reduction, altered myelination of the motor cortex, cerebellar atrophy, enlargement of the ventricles, and subcellular alterations of endoplasmic reticulum and Golgi apparatus compartments. Remarkably, although YIF1B was not detected in primary cilia, biallelic YIF1B mutations caused primary cilia abnormalities in skin fibroblasts from both patients and Yif1b-KO mice, and in ciliary architectural components in the Yif1b-KO brain. Consequently, our findings identify YIF1B as an essential gene in early post-natal development in human, and provide a new genetic target that should be tested in patients developing a neurodevelopmental delay during the first year of life. Thus, our work is the first description of a functional deficit linking Golgipathies and ciliopathies, diseases so far associated exclusively to mutations in genes coding for proteins expressed within the primary cilium or related ultrastructures. We therefore propose that these pathologies should be considered as belonging to a larger class of neurodevelopmental diseases depending on proteins involved in the trafficking of proteins towards specific cell membrane compartments.

Bi-allelic pathogenic variants in NDUFC2 cause early-onset Leigh syndrome and stalled biogenesis of complex I

Leigh syndrome is a progressive neurodegenerative disorder, most commonly observed in paediatric mitochondrial disease, and is often associated with pathogenic variants in complex I structural subunits or assembly factors resulting in isolated respiratory chain complex I deficiency. Clinical heterogeneity has been reported, but key diagnostic findings are developmental regression, elevated lactate and characteristic neuroimaging abnormalities. Here, we describe three affected children from two unrelated families who presented with Leigh syndrome due to homozygous variants (c.346_*7del and c.173A>T p.His58Leu) in NDUFC2, encoding a complex I subunit. Biochemical and functional investigation of subjects’ fibroblasts confirmed a severe defect in complex I activity, subunit expression and assembly. Lentiviral transduction of subjects’ fibroblasts with wild‐type NDUFC2 cDNA increased complex I assembly supporting the association of the identified NDUFC2 variants with mitochondrial pathology. Complexome profiling confirmed a loss of NDUFC2 and defective complex I assembly, revealing aberrant assembly intermediates suggestive of stalled biogenesis of the complex I holoenzyme and indicating a crucial role for NDUFC2 in the assembly of the membrane arm of complex I, particularly the ND2 module.

Clinical, molecular, and biochemical delineation of asparagine synthetase deficiency in Saudi cohort

PURPOSE

Asparagine synthetase deficiency (ASNSD) is a rare neurometabolic disease. Patients may not demonstrate low asparagine levels, which highlights the advantage of molecular over biochemical testing in the initial work-up of ASNSD. We aimed to further delineate the ASNSD variant and phenotypic spectrum and determine the value of biochemical testing as a frontline investigation in ASNSD.

METHODS

We retrospectively collected the clinical and molecular information on 13 families with ASNSD from the major metabolic clinics in Saudi Arabia.

RESULTS

The major phenotypes included congenital microcephaly (100%), facial dysmorphism (100%), global developmental delay (100%), brain abnormalities (100%), spasticity (86%), and infantile-onset seizures (93%). Additional unreported phenotypes included umbilical hernia, osteopenia, eczema, lung hypoplasia, and hearing loss. Overall, seven homozygous variants accounted for ASNSD. The p.Tyr398Cys and p.Asn75Ile variants accounted for 54% of the cases. The clinical sensitivity and specificity of the proposed biochemical analysis of cerebrospinal fluid (CSF) for the detection of patients with ASNSD were 83% and 98%, respectively.

CONCLUSION

Our study describes the largest reported ASNSD cohort with clinical, molecular, and biochemical characterization. Taking into consideration the suboptimal sensitivity of biochemical screening, the delineation of the phenotype variant spectrum is of diagnostic utility for accurate diagnosis, prognosis, counseling, and carrier screening.

Expanding the clinical and genetic spectra of NKX6-2-related disorder

Hypomyelinating leukodystrophies (HLDs) affect the white matter of the central nervous system and manifest as neurological disorders. They are genetically heterogeneous. Very recently, biallelic variants in NKX6-2 have been suggested to cause a novel form of autosomal recessive HLD. Using whole-exome or whole-genome sequencing, we identified the previously reported c.196delC and c.487C>G variants in NKX6-2 in 3 and 2 unrelated index cases, respectively; the novel c.608G>A variant was identified in a sixth patient. All variants were homozygous in affected family members only. Our patients share a primary diagnosis of psychomotor delay, and they show spastic quadriparesis, nystagmus and hypotonia. Seizures and dysmorphic features (observed in 2 families each) represent an addition to the phenotype, while developmental regression (observed in 3 families) appears to be a notable and previously underestimated clinical feature. Our findings extend the clinical and mutational spectra associated with this novel form of HLD. Comparative analysis of our 10 patients and the 15 reported previously did, however, not reveal clear evidence for a genotype-phenotype correlation.

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.

Biallelic inactivating variants in the GTPBP2 gene cause a neurodevelopmental disorder with severe intellectual disability

Congenital neurological disorders are genetically highly heterogeneous. Rare forms of hereditary neurological disorders are still difficult to be adequately diagnosed. Pertinent studies, especially when reporting only single families, need independent confirmation. We present three unrelated families in which whole-exome sequencing identified the homozygous non-sense variants c.430[C>T];[C>T] p.(Arg144*), c.1219[C>T];[C>T] p.(Gln407*) and c.1408[C>T];[C>T] p.(Arg470*) in GTPBP2. Their clinical presentations include early onset and apparently non-progressive motor and cognitive impairment, and thereby overlap with findings in a recently described family harbouring a homozygous GTPBP2 splice site variant. Notable differences include structural brain abnormalities (e.g., agenesis of the corpus callosum, exclusive to our patients), and evidence for brain iron accumulation (exclusive to the previously described family). This report confirms pathogenicity of biallelic GTPBP2 inactivation and broadens the phenotypic spectrum. It also underlines that a potential involvement of brain iron accumulation needs clarification. Further patients will have to be identified and characterised in order to fully define the core features of GTPBP2-associated neurological disorder, but future approaches to molecular diagnosis of neurodevelopmental disorders should implement GTPBP2.

Urea cycle disorder misdiagnosed as multiple sclerosis: a case report and review of the literature

Urea cycle disorders are a group of inborn errors of metabolism caused by dysfunction of any of the six enzymes or two transport proteins involved in urea biosynthesis. In this paper, we report a patient who presented with neurological dysfunction and coma in the immediate postpartum period. She was misdiagnosed for many years as a case of multiple sclerosis. The importance of reporting this case is to illustrate that the wrong diagnosis of patients as being affected with multiple sclerosis for many years due to magnetic resonance imaging abnormalities rather than the classic relapsing-remitting nature of the disease may lead to catastrophic consequences. The patient was treated with intravenous steroids several times, which is contraindicated in patients with urea cycle disorders as it may precipitate acute hyperammonemic attacks. In addition, the management of urea cycle disorder could have started earlier and avoided multiple admissions to the intensive care unit. We believe that the presence of symmetric hyperintense insular cortical changes are seen in multiple hyperammonemic processes, and in the context of the clinical presentation and high ammonia levels can be suggestive of a urea cycle disorder. For any patient presenting with atypical clinical features, images should be reviewed and discussed in detail with an experienced neuroradiologist. In addition, the ammonia levels should be checked if a urea cycle disorder is suspected.

Phenotypic heterogeneity in Woodhouse-Sakati syndrome: two new families with a mutation in the C2orf37 gene

Hypogonadism, alopecia, diabetes mellitus, mental retardation, and extrapyramidal syndrome [also known as Woodhouse-Sakati syndrome (WSS)] is a rare autosomal recessive neuroendocrine and ectodermal disorder. The syndrome was first described by Woodhouse and Sakati in 1983, and 47 patients from 23 families have been reported so far. We report on an additional seven patients (four males and three females) from two highly consanguineous Arab families from Qatar, presenting with a milder phenotype of WSS. These patients show the spectrum of clinical features previously found in WSS, but lack evidence of diabetes mellitus and extrapyramidal symptoms. These two new families further illustrate the natural course and the interfamilial phenotypic variability of WSS that may lead to challenges in making the diagnosis. In addition, our study suggests that WSS may not be as infrequent in the Arab world as previously thought.