Germline homozygous missense DEPDC5 variants cause severe refractory early-onset epilepsy, macrocephaly and bilateral polymicrogyria.

DEPDC5 (DEP Domain-Containing Protein 5) encodes an inhibitory component of the mammalian target of rapamycin (mTOR) pathway and is commonly implicated in sporadic and familial focal epilepsies, both non-lesional and in association with focal cortical dysplasia. Germline pathogenic variants are typically heterozygous and inactivating. We describe a novel phenotype caused by germline biallelic missense variants in DEPDC5. Cases were identified clinically. Available records, including magnetic resonance imaging and electroencephalography, were reviewed. Genetic testing was performed by whole exome and whole-genome sequencing and cascade screening. In addition, immunohistochemistry was performed on skin biopsy. The phenotype was identified in nine children, eight of which are described in detail herein. Six of the children were of Irish Traveller, two of Tunisian and one of Lebanese origin. The Irish Traveller children shared the same DEPDC5 germline homozygous missense variant (p.Thr337Arg), whereas the Lebanese and Tunisian children shared a different germline homozygous variant (p.Arg806Cys). Consistent phenotypic features included extensive bilateral polymicrogyria, congenital macrocephaly and early-onset refractory epilepsy, in keeping with other mTOR-opathies. Eye and cardiac involvement and severe neutropenia were also observed in one or more patients. Five of the children died in infancy or childhood; the other four are currently aged between 5 months and 6 years. Skin biopsy immunohistochemistry was supportive of hyperactivation of the mTOR pathway. The clinical, histopathological and genetic evidence supports a causal role for the homozygous DEPDC5 variants, expanding our understanding of the biology of this gene.

MPC2 variants disrupt mitochondrial pyruvate metabolism and cause an early-onset mitochondriopathy.

Pyruvate is an essential metabolite produced by glycolysis in the cytosol and must be transported across the inner mitochondrial membrane into the mitochondrial matrix, where it is oxidized to fuel mitochondrial respiration. Pyruvate import is performed by the mitochondrial pyruvate carrier (MPC), a hetero-oligomeric complex composed by interdependent subunits MPC1 and MPC2. Pathogenic variants in the MPC1 gene disrupt mitochondrial pyruvate uptake and oxidation and cause autosomal-recessive early-onset neurological dysfunction in humans. The present work describes the first pathogenic variants in MPC2 associated with human disease in four patients from two unrelated families. In the first family, patients presented with antenatal developmental abnormalities and harboured a homozygous c.148T>C (p.Trp50Arg) variant. In the second family, patients that presented with infantile encephalopathy carried a missense c.2T>G (p.Met1?) variant disrupting the initiation codon. Patient-derived skin fibroblasts exhibit decreased pyruvate-driven oxygen consumption rates with normal activities of the pyruvate dehydrogenase complex and mitochondrial respiratory chain and no defects in mitochondrial content or morphology. Re-expression of wild-type MPC2 restored pyruvate-dependent respiration rates in patient-derived fibroblasts. The discovery of pathogenic variants in MPC2 therefore broadens the clinical and genetic landscape associated with inborn errors in pyruvate metabolism.

Plasma GM2 ganglioside potential biomarker for diagnosis, prognosis and disease monitoring of GM2-Gangliosidosis.

GM2-Gangliosidosis are a group of inherited lysosomal storage pathologies characterized by a large accumulation of GM2 ganglioside in the lysosome. They are caused by mutation in HEXA or HEXB causing reduced or absent activity of a lysosomal ß-hexosaminidase A, or mutation in GM2A causing defect in GM2 activator protein (GM2AP), an essential protein for the activity of the enzyme. Biochemical diagnosis relies on the measurement of ß-hexosaminidases A and B activities, which is able to detect lysosomal enzyme deficiency but fails to identify defects in GM2AP. We developed a rapid, specific and sensitive liquid chromatography-mass spectrometry-based method to measure simultaneously GM1, GM2, GM3 and GD3 molecular species. Gangliosides were analysed in plasma from 19 patients with GM2-Gangliosidosis: Tay-Sachs (n = 9), Sandhoff (n = 9) and AB variant of GM2-Gangliosidosis (n = 1) and compared to 20 age-matched controls. Among patients, 12 have a late adult-juvenile-onset and 7 have an infantile early-onset of the disease. Plasma GM2 molecular species were increased in all GM2-Gangliosidosis patients (19/19), including the patient with GM2A mutation, compared to control individuals and compared to patients with different other lysosomal storage diseases. GM234:1 and GM234:1/GM334:1 ratio discriminated patients from controls with 100% sensitivity and specificity. GM234:1 and GM234:1/GM334:1 were higher in patients with early-onset compared to those with late-onset of the disease, suggesting a relationship with severity. Longitudinal analysis in one adult with Tay-Sachs disease over 9 years showed a positive correlation of GM234:1 and GM234:1/GM334:1 ratio with age at sampling. We propose that plasma GM2 34:1 and its ratio to GM3 34:1 could be sensitive and specific biochemical diagnostic biomarkers for GM2-Gangliosidosis including AB variant and could be useful as a first line diagnostic test and potential biomarkers for monitoring upcoming therapeutic efficacy.

Neuronal ceroïd-lipofuscinosis: Clinical, electroencephalographic, imaging, and genetic study of a maghrebian series.

Our study included 13 patients diagnosed with neuronal ceroidlipofuscinosis. It is a group of rare genetically-determined neurodegenerativediseases characterized by clinical and genetic heterogeneity. brain MRI andelectroencephalogram facilitate diagnosis.

Hypomyelination and Congenital Cataract: Clinical, Imaging, and Genetic Findings in Three Tunisian Families and Literature Review.

Hypomyelination and congenital cataract (HCC) is characterized by congenital cataract, progressive neurologic impairment, and diffuse myelin deficiency. This autosomal recessive disorder is caused by homozygous variant in the FAM126A gene. Five consanguineous Tunisian patients, belonging to three unrelated families, underwent routine blood tests, electroneuromyography, and magnetic resonance imaging of the brain. The direct sequencing of FAM126A exons was performed for the patients and their relatives. We summarized the 30 previously published HCC cases. All of our patients were carriers of a previously reported c.414 + 1G > T (IVS5 + 1G > T) variant, but the clinical spectrum was variable. Despite the absence of a phenotype-genotype correlation in HCC disease, screening of this splice site variant should be performed in family members at risk.

Acute Movement Disorders in Childhood: A Cohort Study and Review of the Literature.

OBJECTIVES: Acute movement disorders (AMD) are frequent in neurological and pediatric emergencies. Few studies analyzed AMD in children, none in Tunisia or other African country. The purpose of this study was to describe the peculiarities of AMD in a Tunisian pediatric population with a literature review. METHODS: We conducted a retrospective descriptive study over 8 years including 80 children (sex ratio, 1.05; mean age of onset, 4.8 years) with AMD, followed in tertiary referral Child Neurology Department in North Tunisia. RESULTS: Acute movement disorders were mainly hyperkinetic (n = 67 with dystonia (n = 33; mostly due to inherited metabolic diseases (IMD) in 11; with status epilepticus in 10 children), chorea (n = 14; with Sydenham chorea in 5); myoclonus (n = 14; mostly with opsoclonus-myoclonus syndrome in 10) and tremor (n = 6; of posttraumatic origin in half). Hypokinetic movement disorder (MD) included acute parkinsonism in 5 children of infectious (n = 3), postinfectious (n = 1, malaria) and posttraumatic origin (n = 1). Mixed MD, found in 8 children, were mainly due to IMD in half of them, and to familial lupus in two. Paroxysmal MDs were seen in 2 children, one with multiple sclerosis and one of idiopathic origin. Psychogenic MDs were found in 7 patients mainly of dystonic type. Management of AMD comprised symptomatic treatment according to the phenomenology of the MD and causative treatment depending on its etiology. CONCLUSIONS: Our study illustrated the broad range of AMD in children and the wide spectrum of their etiologies. In our series, we described some exceptional findings and etiologies of AMD in children. These findings may denote a specific profile in of AMD in our country with predominant infectious, postinfectious, and IMD.

MECR Mutations Cause Childhood-Onset Dystonia and Optic Atrophy, a Mitochondrial Fatty Acid Synthesis Disorder.

Mitochondrial fatty acid synthesis (mtFAS) is an evolutionarily conserved pathway essential for the function of the respiratory chain and several mitochondrial enzyme complexes. We report here a unique neurometabolic human disorder caused by defective mtFAS. Seven individuals from five unrelated families presented with childhood-onset dystonia, optic atrophy, and basal ganglia signal abnormalities on MRI. All affected individuals were found to harbor recessive mutations in MECR encoding the mitochondrial trans-2-enoyl-coenzyme A-reductase involved in human mtFAS. All six mutations are extremely rare in the general population, segregate with the disease in the families, and are predicted to be deleterious. The nonsense c.855T>G (p.Tyr285∗), c.247_250del (p.Asn83Hisfs∗4), and splice site c.830+2_830+3insT mutations lead to C-terminal truncation variants of MECR. The missense c.695G>A (p.Gly232Glu), c.854A>G (p.Tyr285Cys), and c.772C>T (p.Arg258Trp) mutations involve conserved amino acid residues, are located within the cofactor binding domain, and are predicted by structural analysis to have a destabilizing effect. Yeast modeling and complementation studies validated the pathogenicity of the MECR mutations. Fibroblast cell lines from affected individuals displayed reduced levels of both MECR and lipoylated proteins as well as defective respiration. These results suggest that mutations in MECR cause a distinct human disorder of the mtFAS pathway. The observation of decreased lipoylation raises the possibility of a potential therapeutic strategy.

Muscle-Specific Kinase Autoimmune Myasthenia Gravis: Report of a Pediatric Case and Literature Review.

Myasthenia gravis (MG) with antibodies to the muscle-specific tyrosine kinase (MuSK-MG) receptor is a rare entity. It represents 5 to 8% of all MG patients. Few pediatric cases were reported. Clinical presentation is often atypical. It is characterized by predominant involvement of cranial, bulbar, and axial muscles and early respiratory crises. Myokymia and fasciculation are suggestive of MuSK-MG. The clinical course of patients with MuSK-MG is worse than other types of MG. Responses to standard therapies are variable. We report clinical, neurophysiological, serological, and outcome profile of a Tunisian child with MuSK-MG.

Early Life Epilepsy and Episodic Apnea Revealing an ATP1A3 Mutation: Report of a Pediatric Case and Literature Review.

ATP1A3 mutations have now been recognized in infants, children, and adults presenting with a diverse group of neurological phenotypes, including rapid-onset dystonia-parkinsonism, alternating hemiplegia of childhood, and most recently, cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss syndrome. The phenotypic spectrum of ATP1A3-related neurological disorders continues to expand. In this case study, we report on early life epilepsy with episodic apnea potentially secondary to ATP1A3 mutation in a Tunisian child.

Mutations in CEP120 cause Joubert syndrome as well as complex ciliopathy phenotypes.

BACKGROUND: Ciliopathies are an extensive group of autosomal recessive or X-linked disorders with considerable genetic and clinical overlap, which collectively share multiple organ involvement and may result in lethal or viable phenotypes. In large numbers of cases the genetic defect remains yet to be determined. The aim of this study is to describe the mutational frequency and phenotypic spectrum of the CEP120 gene. METHODS: Exome sequencing was performed in 145 patients with Joubert syndrome (JS), including 15 children with oral-facial-digital syndrome type VI (OFDVI) and 21 Meckel syndrome (MKS) fetuses. Moreover, exome sequencing was performed in one fetus with tectocerebellar dysraphia with occipital encephalocele (TCDOE), molar tooth sign and additional skeletal abnormalities. As a parallel study, 346 probands with a phenotype consistent with JS or related ciliopathies underwent next-generation sequencing-based targeted sequencing of 120 previously described and candidate ciliopathy genes. RESULTS: We present six probands carrying nine distinct mutations (of which eight are novel) in the CEP120 gene, previously found mutated only in Jeune asphyxiating thoracic dystrophy (JATD). The CEP120-associated phenotype ranges from mild classical JS in four patients to more severe conditions in two fetuses, with overlapping features of distinct ciliopathies that include TCDOE, MKS, JATD and OFD syndromes. No obvious correlation is evident between the type or location of identified mutations and the ciliopathy phenotype. CONCLUSION: Our findings broaden the spectrum of phenotypes caused by CEP120 mutations that account for nearly 1% of patients with JS as well as for more complex ciliopathy phenotypes. The lack of clear genotype-phenotype correlation highlights the relevance of comprehensive genetic analyses in the diagnostics of ciliopathies.

X-linked Adrenoleukodystrophy, The Tunisian Experience.

BACKGROUND: X-linked adrenoleukodystrophy is a genetic disease affecting the degradation of very long chain fatty acids. This study aims to describe the clinical phenotype and biochemical feature of Tunisian patients; it also seeks to describe recognition of pattern analysis on the level of very long chain fatty acids in plasma for the visual discrimination of X-linked patients from a healthy group. METHODS: During the last 21 years, 19 patients were diagnosed with X-linked adrenoleukodystrophy based on the clinical features combined with the area percentage of hexacosanoic acid (C26:0) as well as the ratio of C26:0 and lignoceric acid (C24:0) relative to behenic acid (C22:0) by gas chromatography. For the biochemical diagnosis of X-ALD with better accuracy, it has been desired to transform the numerical values of these biochemical markers into visually discriminating patterns. RESULTS: The clinical features of 19 patients aged between 4 to 47 years were classified into cerebral form (57.8%), adrenomyeloneuropathic (26.3%), and a few patients were asymptomatic. The ratio C24:0/C22:0 ranged from 1.12 to 2.41 (normal value: 0.46 - 0.9) and C26:0/C22:0 ratio ranged from 0.03 to 0.36 (normal value: 0.003 - 0.009). The concentration of fatty acids with 22 or more carbons in body fluid did not change with age in control subjects and patients. For the visual diagnostic of patients, the Scatter plot was a reliable method for the diagnostic patterns of very long chain fatty acids of patients with X-linked adrenoleukodystrophy disorders. CONCLUSIONS: The incidence of X-linked adrenoleukodystrophy disorders is under diagnosed in Tunisia. The diagnosis was confirmed by enzymatic activity study and molecular analysis but the analysis of very long chain fatty acids by gas chromatography remains a reliable tool for the diagnosis and early initiation of the treatment.

Status dystonicus in childhood.

BACKGROUND: Status Dystonicus is a rare complication of dystonia. It is a life threatening disorder that needs urgent treatment.The aim of this study is to describe clinical features, management and follow up of children with Status Dystonicus. METHODS: - We conducted a retrospective study over an 8-year period including all patients diagnosed with Status Dystonicus. Clinical characteristics, etiologies and management were analyzed. RESULTS: - Ten patients were included. Main features of Status Dystonicus were a severe generalized dystonia with vegetative signs. Laryngeal spasm and swallowing disorders were observed in 4 cases. Several treatments such as Levodopa, Anticholinergics, Baclofen, Benzodiazepines and Neuroleptics were tried. Mechanical ventilation was required in 4 cases. Two patients died due to rhabdomyolysis and respiratory failure. Others returned to their pre-Status Dystonicus. CONCLUSION: - Status Dystonicus is a life threatening condition that needs an urgent management on an intensive care unit. In fact, patients with Status Dystonicus can develop respiratory failure and metabolic complications.On the basis of our experience, we delineated a therapeutic approach in which the patient with Status Dystonicus needs supportive care, specific therapy of dystonia and intravenous sedative treatment.

Immunity in the Progeroid Model of Cockayne Syndrome: Biomarkers of Pathological Aging.

Cockayne syndrome (CS) is a rare autosomal recessive disorder that affects the DNA repair process. It is a progeroid syndrome predisposing patients to accelerated aging and to increased susceptibility to respiratory infections. Here, we studied the immune status of CS patients to determine potential biomarkers associated with pathological aging. CS patients, as well as elderly and young, healthy donors, were enrolled in this study. Complete blood counts for patients and donors were assessed, immune cell subsets were analyzed using flow cytometry, and candidate cytokines were analyzed via multi-analyte ELISArray kits. In CS patients, we noticed a high percentage of lymphocytes, an increased rate of intermediate and non-classical monocytes, and a high level of pro-inflammatory cytokine IL-8. In addition, we identified an increased rate of particular subtypes of T Lymphocyte CD8+ CD28- CD27-, which are senescent T cells. Thus, an inflammatory state was found in CS patients that is similar to that observed in the elderly donors and is associated with an immunosenescence status in both groups. This could explain the CS patients' increased susceptibility to infections, which is partly due to an aging-associated inflammation process.

Single-center experience of congenital disorders of glycosylation syndrome screening in Tunisia: A retrospective study over a 15-year period (2007-2021).

BACKGROUND: We report the results gathered over 15 years of screening for congenital disorders of glycosylation syndrome (CDGS) in Tunisia according to clinical and biochemical characteristics. METHODS: Our laboratory received 1055 analysis requests from various departments and hospitals, for children with a clinical suspicion of CDGS. The screening was carried out through separation of transferrin isoforms by capillary zone electrophoresis. RESULTS: During the 15-year period, 23 patients were diagnosed with CDGS (19 patients with CDG-Ia, three patients with CDG-IIx, and one patient with CDG-X). These patients included 13 boys and 10 girls aged between 3 months and 13 years, comprising 2.18 % of the total 1055 patients screened. The incidence for CDGS was estimated to be 1:23,720 live births (4.21 per 100,000) in Tunisia. The main clinical symptoms related to clinical disease state in newborn and younger patients were psychomotor retardation (91 %), cerebellar atrophy (91 %), ataxia (61 %), strabismus (48 %), dysmorphic symptoms (52 %), retinitis pigmentosa, cataract (35 %), hypotonia (30 %), and other symptoms. CONCLUSION: In Tunisia, CDGS still remains underdiagnosed or misdiagnosed. The resemblance to other diseases, especially neurological disorders, and physicians' unawareness of the existence of these diseases are the main reasons for the underdiagnosis. In routine diagnostics, the screening for CDGS by biochemical tests is mandatory to complete the clinical diagnosis.

Current phenotypic and genetic spectrum of syndromic deafness in Tunisia: paving the way for precision auditory health.

Hearing impairment (HI) is a prevalent neurosensory condition globally, impacting 5% of the population, with over 50% of congenital cases attributed to genetic etiologies. In Tunisia, HI underdiagnosis prevails, primarily due to limited access to comprehensive clinical tools, particularly for syndromic deafness (SD), characterized by clinical and genetic heterogeneity. This study aimed to uncover the SD spectrum through a 14-year investigation of a Tunisian cohort encompassing over 700 patients from four referral centers (2007-2021). Employing Sanger sequencing, Targeted Panel Gene Sequencing, and Whole Exome Sequencing, genetic analysis in 30 SD patients identified diagnoses such as Usher syndrome, Waardenburg syndrome, cranio-facial-hand-deafness syndrome, and H syndrome. This latter is a rare genodermatosis characterized by HI, hyperpigmentation, hypertrichosis, and systemic manifestations. A meta-analysis integrating our findings with existing data revealed that nearly 50% of Tunisian SD cases corresponded to rare inherited metabolic disorders. Distinguishing between non-syndromic and syndromic HI poses a challenge, where the age of onset and progression of features significantly impact accurate diagnoses. Despite advancements in local genetic characterization capabilities, certain ultra-rare forms of SD remain underdiagnosed. This research contributes critical insights to inform molecular diagnosis approaches for SD in Tunisia and the broader North-African region, thereby facilitating informed decision-making in clinical practice.

3-Phosphoglycerate dehydrogenase deficiency: description of two new cases in Tunisia and review of the literature.

3-Phosphoglycerate dehydrogenase (3-PGDH) deficiency is a rare autosomal recessive disorder of serine biosynthesis. It is typically characterized by congenital microcephaly, intractable seizures of infantile onset, and severe psychomotor retardation. Diagnosis is suspected on decreased l-serine levels in plasma and cerebrospinal fluid (CSF) and confirmed by genetic study. Early diagnosis in index cases allows supplementation in serine and prevention of fixed lesions. Prenatal diagnosis and genetic counseling allows prevention of secondary cases. We report on the two first unrelated Tunisian families with 3-PGDH deficiency confirmed by biochemical and genetic study. We discuss clinical, biochemical, imaging, electroencephalographic, and therapeutic aspects and review the literature.

Pediatric Neurotuberculosis: A cases series and review of the literature.

Neurotuberculosis or central nervous system tuberculosis is a form of tuberculous infection that affects any part of the nervous system. Although it is more frequent in adults, pediatric cases have been reported in endemic countries and it is potentially a deadly affection. Therefore, any unusual neurological manifestation in a formerly healthy child, independently of their vaccination status, must bring suspicion of CNS tuberculosis among other diagnoses. We report four cases of pediatric neurotuberculosis with various clinical presentations and outcome and a brief review of the litterature. We conclude that clinical manifestations of pediatric neurotuberculosis are extremely variable and could be misleading. Extra-neurological sites are a key element for diagnosis especially in the pediatric population. A diagnosis and clinical outcome score, especially designed for children might help personalize the therapeutic approach and outcome measures.

Expanding the genetic spectrum of mitochondrial diseases in Tunisia: novel variants revealed by whole-exome sequencing.

Introduction: Inherited mitochondrial diseases are the most common group of metabolic disorders caused by a defect in oxidative phosphorylation. They are characterized by a wide clinical and genetic spectrum and can manifest at any age. In this study, we established novel phenotype-genotype correlations between the clinical and molecular features of a cohort of Tunisian patients with mitochondrial diseases. Materials and methods: Whole-exome sequencing was performed on five Tunisian patients with suspected mitochondrial diseases. Then, a combination of filtering and bioinformatics prediction tools was utilized to assess the pathogenicity of genetic variations. Sanger sequencing was subsequently performed to confirm the presence of potential deleterious variants in the patients and verify their segregation within families. Structural modeling was conducted to study the effect of novel variants on the protein structure. Results: We identified two novel homozygous variants in NDUFAF5 (c.827G>C; p.Arg276Pro) and FASTKD2 (c.496_497del; p.Leu166GlufsTer2) associated with a severe clinical form of Leigh and Leigh-like syndromes, respectively. Our results further disclosed two variants unreported in North Africa, in GFM2 (c.569G>A; p.Arg190Gln) and FOXRED1 (c.1261G>A; p.Val421Met) genes, and we described the first case of fumaric aciduria in a Tunisian patient harboring the c.1358T>C; p.Leu453Pro FH variant. Conclusion: Our study expands the mutational and phenotypic spectrum of mitochondrial diseases in Tunisia and highlights the importance of next-generation sequencing to decipher the pathomolecular mechanisms responsible for these disorders in an admixed population.

Guanidinoacetate methyltransferase (GAMT) deficiency in two Tunisian siblings: clinical and biochemical features.

BACKGROUND: Guanidinoacetate methyltransferase (GAMT) deficiency is a recently described disorder and few cases have been reported to date. As it is a treatable pathology, we seek to contribute to its better understanding, particularly to further elucidate its biochemical diagnosis for early treatment. METHODS: The patients, two brothers aged 13 years (P1) and 11 years (P2), have been explored for signs and symptoms suggestive of inborn errors of metabolism. The quantification of creatine (Cr), guanidinoacetate (GAA), and GAMT activity was performed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). RESULTS: The two brothers presented a similar clinical picture: developmental delay, epilepsy, axial hypotonia, spastic tetraparesis, severe mental and language delay, and autistic behaviour. GAA concentrations were markedly increased in plasma and in urine [2796 and 3342 micromol/mmol creatinine (control range: 4 - 220 micromol/mmol creatinine)/14 and 29 micromol/L (control range: 0.35 - 1.8 micromol/L), respectively] while plasma and urine creatine concentrations were at the lower normal range limit. Activity of GAMT in lymphoblasts was extremely reduced (< 0.01 nmol/mg protein/hour) compared to healthy subjects. GAMT activity was found to be intermediary in patients' parents. CONCLUSIONS: It appears that the clinical picture is heterogeneous but should be considered as potential signs of creatine metabolism disorders, however, the biochemical diagnosis is reliable as the enzyme activity is zero in most cases. To date, it is still too early to establish correlations between symptoms and biochemical profile. However, the identification of additional cases of GAMT deficiency should help elucidate such relationships and the progress of patients treated with creatine in conjunction with ornithine supplementation.

Heterogeneous clinical features in Cockayne syndrome patients and siblings carrying the same CSA mutations.

BACKGROUND: Cockayne syndrome (CS) is a rare autosomal recessive disorder caused by mutations in ERCC6/CSB or ERCC8/CSA that participate in the transcription-coupled nucleotide excision repair (TC-NER) of UV-induced DNA damage. CS patients display a large heterogeneity of clinical symptoms and severities, the reason of which is not fully understood, and that cannot be anticipated in the diagnostic phase. In addition, little data is available for affected siblings, and this disease is largely undiagnosed in North Africa. METHODS: We report here the clinical description as well as genetic and functional characterization of eight Tunisian CS patients, including siblings. These patients, who belonged to six unrelated families, underwent complete clinical examination and biochemical analyses. Sanger sequencing was performed for the recurrent mutation in five families, and targeted gene sequencing was done for one patient of the sixth family. We also performed Recovery RNA Synthesis (RRS) to confirm the functional impairment of DNA repair in patient-derived fibroblasts. RESULTS: Six out of eight patients carried a homozygous indel mutation (c.598_600delinsAA) in exon 7 of ERCC8, and displayed a variable clinical spectrum including between siblings sharing the same mutation. The other two patients were siblings who carried a homozygous splice-site variant in ERCC8 (c.843+1G>C). This last pair presented more severe clinical manifestations, which are rarely associated with CSA mutations, leading to gastrostomy and hepatic damage. Impaired TC-NER was confirmed by RRS in six tested patients. CONCLUSIONS: This study provides the first deep characterization of case series of CS patients carrying CSA mutations in North Africa. These mutations have been described only in this region and in the Middle-East. We also provide the largest characterization of multiple unrelated patients, as well as siblings, carrying the same mutation, providing a framework for dissecting elusive genotype-phenotype correlations in CS.