Absent meibomian glands and cone dystrophy in ADULT syndrome: identification by whole exome sequencing of pathogenic variants in two causal genes TP63 and CNGB3.

BACKGROUND: Ectrodactyly is a rare congenital limb malformation characterized by a deep median cleft of the hand and/or foot due to the absence of central rays. It could be isolated or depicts a part of diverse syndromic forms. Heterozygous pathogenic variants in the TP63 gene are responsible for at least four rare syndromic human disorders associated with ectrodactyly. Among them, ADULT (Acro-Dermato-Ungual-Lacrimal-Tooth) syndrome is characterized by ectodermal dysplasia, excessive freckling, nail dysplasia, and lacrimal duct obstruction, in addition to ectrodactyly and/or syndactyly. Ophthalmic findings are very common in TP63-related disorders, consisting mainly of lacrimal duct hypoplasia. Absent meibomian glands have also been well documented in EEC3 (Ectrodactyly Ectodermal dysplasia Cleft lip/palate) syndrome but not in ADULT syndrome. METHODS: We report a case of syndromic ectrodactyly consistent with ADULT syndrome, with an additional ophthalmic manifestation of agenesis of meibomian glands. The proband, as well as her elder sister, presented with congenital cone dystrophy.The molecular investigation was performed in the proband using Whole Exome Sequencing. Family segregation of the identified variants was confirmed by Sanger sequencing. RESULTS: Two clinically relevant variants were found in the proband: the novel de novo heterozygous missense c.931A > G (p.Ser311Gly) in the TP63 gene classified as pathogenic, and the homozygous nonsense pathogenic c.1810C > T (p.Arg604Ter) in the CNGB3 gene. The same homozygous CNGB3 variation was also found in the sister, explaining the cone dystrophy in both cases. CONCLUSIONS: Whole Exome Sequencing allowed dual molecular diagnoses: de novo TP63-related syndromic ectrodactyly and familial CNGB3-related congenital cone dystrophy.

A novel WFS1 variant associated with severe diabetic retinopathy in Wolfram syndrome type 1.

BACKGROUND: Wolfram syndrome type 1 is a rare neurodegenerative disorder including diabetes insipidus, diabetes mellitus, optic atrophy, and deafness, with variable additional findings. The phenotypic spectrum is very heterogeneous, with non-autoimmune juvenile-onset diabetes and optic atrophy as minimal criteria for the diagnosis. Biallelic mutations in the WFS1 gene are the causative genetic anomaly for the syndrome, with, however, no evident genotype-phenotype correlation. Among the clinical features of the disease, diabetic retinopathy depicts a rarely reported microvascular complication. In this report, we describe the clinical and genetic findings in a 26-year-old patient presenting with Wolfram syndrome and severe diabetic retinopathy. METHODS: The mutation screening was performed by polymerase chain reaction followed by Sanger sequencing of the entire coding sequence of the WFS1 gene. RESULTS: A novel homozygous missense variant c.1901A>T (p.Lys634Met) was found in the proband and classified as probably pathogenic according to the American College of Medical Genetics and Genomics. CONCLUSIONS: The molecular study of the WFS1 gene is essential for the diagnostic confirmation, to provide appropriate genetic counseling and a mutational screening in the at-risk relatives. The c.1901A>T (p.Lys634 Met) is a novel variant that could be responsible for a severe form of Wolfram syndrome with early and proliferative diabetic retinopathy.

A rare homozygous p.Arg87Trp variant of the GBA gene in Gaucher disease: A case report.

Gaucher disease (GD) is a rare metabolic disorder due to pathogenic variants in the GBA gene. We report the first case of the rare p.Arg87Trp pathogenic variant (formerly known as R48W) of the GBA gene in the Tunisian population. A female Arab patient was assessed at the age of 26 due to abdominal distension, bone pain, and headache since she was 25. Physical examination revealed splenomegaly, rib deformation, lumbar scoliosis, and upper limb tremor. Bone marrow was infiltrated by Gaucher cells. The patient was homozygous for the rare p.Arg87Trp variant which is known to be associated with a mild phenotype. This report highlights the necessity of screening the Tunisian population for this rare variant.

Beckwith-Wiedemann syndrome: Clinical, histopathological and molecular study of two Tunisian patients and review of literature.

BACKGROUND: Beckwith-Wiedemann syndrome (BWS) is a rare overgrowth syndrome characterized by congenital malformations and predisposition to embryonic tumors. Loss of methylation of imprinting center 2 (IC2) is the most frequent alteration and rarely associated with tumors compared to paternal uniparental disomy of chromosome 11 (UPD(11)pat) and gain of methylation of imprinting center 1. METHODS: Our study aimed to describe the clinical, histopathological and genetic characteristics of two patients and establish genotype-phenotype correlations. The clinical diagnosis was based on the criteria defined by the international expert consensus of BWS. Molecular study of 11p15.5 methylation status was assessed using methylation-specific-multiplex ligation probe amplification (MS-MLPA). RESULTS: Patients were aged 12 months and 3 months and fulfilled the clinical score of BWS. MS-MLPA showed molecular alterations consisting of loss of methylation in IC2 (IC2-LOM) at the maternal allele for one patient and a mosaic UPD(11)pat for the second patient in whom follow-up at 6months revealed adrenocortical carcinoma (ACC) with low grade of malignancy. Molecular subtypes guide the follow-up and tumor surveillance, our major concern. CONCLUSION: We have to take into account the psychological impact of a possible tumor whatever the underlying mechanism is. Nevertheless, the tumor risk remains high for UPD(11)pat. Our study extended the phenotype of BWS with absence of macrosomia in Tunisian patients, contrasting with literature, and added a supplementary case of ACC in the tumor spectrum of BWS patients with UPD(11)pat.

New familial cases of karyomegalic interstitial nephritis with mutations in the FAN1 gene.

BACKGROUND: Karyomegalic interstitial nephritis (KIN) is a rare disease entity first described by Burry in 1974. The term KIN was introduced by Mihatsch et al. in 1979. KIN is characterized by chronic tubulointerstitial nephritis associated with enlarged tubular epithelial cell nuclei, which leads to a progressive decline of renal function. The prevalence of this disease is less than 1% of all biopsies, and its pathogenesis is unclear. KIN results from mutations in FAN1 (FANCD2/FANCI-Associated Nuclease 1), a gene involved in the DNA damage response pathway, particularly in the kidney. In this study, we report two Tunisian consanguineous families with KIN caused by mutations in the FAN1 gene. METHODS: Direct sequencing of the coding regions and flanking intronic sequences of the FAN1 gene was performed in three affected members. Three prediction programs (Polyphen-2 software, SIFT, and MutationTaster) were used to predict the functional effect of the detected variations. RESULTS: Two causative frameshift variants in the FAN1 gene were identified in each family: The previously described frameshift mutation c.2616delA (p.Asp873ThrfsTer17) and a novel mutation c.2603delT (p.Leu868ArgfsTer22) classified as "pathogenic" according to the American College of Medical Genetics and Genomics (ACMG) guidelines. CONCLUSION: To our best knowledge, this is the first Tunisian study involving familial cases of KIN with mutations in the FAN1 gene. We hypothesize that these findings can expand the mutational spectrum of KIN and provide valuable information on the genetic cause of KIN.

Mucopolysaccharidosis type VII as a cause of recurrent Non-Immune Hydrops Fetalis: The first Tunisian case confirmed by Next-Generation Sequencing.

Non-Immune Hydrops Fetalis (NIHF) is an intrauterine condition characterized by excessive fluid accumulation in at least two fetal compartments in the absence of maternal circulating red cell antibodies. It is associated with a poor prognosis and a wide etiological spectrum. Among the metabolic causes, Mucopolysaccharidosis type VII depicts the most frequent type of lysosomal storage disorders in the cause of NIHF. Nonetheless, it remains an ultra-rare disorder, as less than 150 cases have been reported in the literature. This rarity seems to be related to misdiagnosis since the underlying etiology remains unelusive in most cases of NIHF. In this report, we describe the first Tunisian case of Mucopolysaccharidosis type VII caused by a homozygous mutation in the GUSB gene confirmed by a Next-Generation Sequencing gene panel in a patient with recurrent NIHF.

First case report of Cohen syndrome in the Tunisian population caused by VPS13B mutations.

BACKGROUND: Cohen syndrome is a rare autosomal recessive developmental disorder that comprises variable clinical features counting developmental delay, pigmentary retinopathy, myopia, acquired microcephaly, truncal obesity, joint hypermobility, friendly disposition and intermittent neutropenia. VPS13B (vacuolar protein sorting 13, yeast, homologue of B) gene is the only gene responsible for Cohen Syndrome, causative mutations include nonsense, missense, indel and splice-site variants. The integrity of the Golgi apparatus requires the presence of the peripheral membrane protein VPS13B that have an essential function in intracellular protein transport and vesicle-mediated sorting. CASE PRESENTATION: In this study, we performed whole exome sequencing (WES) in a Tunisian family with two young cases having developmental delay, hypotonia, autism spectrum disorder, ptosis and thick hair and eyebrows. The proposita presented also pigmentory retinopathy. Compound heterozygous mutation in VPS13B gene was detected by WES. This mutation inherited from healthy heterozygous parents, supports an unpredictable clinical diagnosis of Cohen Syndrome. The proband's phenotype is explained by the presence of compound heterozygous mutations in the VPS13B gene. This finding refined the understanding of genotype-phenotype correlation. CONCLUSIONS: This is the first report of a Tunisian family with Cohen syndrome mutated in the VPS13B gene.

Arg924X homozygous mutation in insulin receptor gene in a Tunisian patient with Donohue syndrome.

Donohue syndrome (DS) is a rare and lethal autosomal recessive disease caused by mutations in the insulin receptor (INSR) gene, manifesting marked insulin resistance, severe growth retardation, hypertrichosis, and characteristic dysmorphic features. We describe a new case of Donohue syndrome born at 37 weeks' gestation of unrelated parents and presented with intra-uterine growth retardation, nipple hypertrophy, macropenis, distended abdomen, hirsutism and dysmorphic features. The clinical course showed failure to thrive, and episodes of alternating hypoglycemia and hyperglycemia. Laboratory tests revealed direct hyperbilirubinemia. The diagnosis of Donohue syndrome was established based on the above clinical characteristics and determination of the INSR mutation. He was found to have homozygous nonsense mutation c. 2270 C>T (Arg924X) at exon 14 of the INSR gene. He later developed enterocolitis and died at 3 months old. Prenatal diagnosis was performed for the family via chorionic villous biopsy. We try to explain gastrointestinal dysfunction seen in our patient.