Expanding the Phenotype of B3GALNT2-Related Disorders

Turicibacter and Catenibacterium as potential biomarkers in autism spectrum disorders

Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by social, behavioral, and cognitive impairments. Several comorbidities, including gastrointestinal (GI) dysregulations, are frequently reported in ASD children. Although studies in animals have shown the crucial role of the microbiota in key aspects of neurodevelopment, there is currently no consensus on how the alteration of microbial composition affects the pathogenesis of ASD. Moreover, disruption of the gut-brain axis (GBA) has been reported in ASD although with limited studies conducted on the Mediterranean population. In our study, we aimed to investigate gut microbiota composition in Lebanese ASD subjects, their unaffected siblings, and a control group from various regions in Lebanon using the 16 S-rRNA sequencing (NGS). Our study revealed a lower abundance of Turicibacter and a significant enrichment on Proteobacteria in the ASD and siblings' groups compared to the controls, indicating that gut microbiota is probably affected by dietary habits, living conditions together with host genetic factors. The study also showed evidence of changes in the gut microbiome of ASD children compared to their siblings and the unrelated control. Bacteroidetes revealed a lower abundance in the ASD group compared to controls and siblings, conversely, Catenibacterium and Tenericutes revealed an increased abundance in the ASD group. Notably, our study identifies alterations in the abundance of Turicibacter and Catenibacterium in ASD children suggesting a possible link between these bacterial taxa and ASD and contributing to the growing body of evidence linking the microbiome to ASD.

Myhre syndrome in adulthood: clinical variability and emerging genotype-phenotype correlations

Myhre syndrome (MS, MIM 139210) is a rare multisystemic disorder caused by recurrent pathogenic missense variants in SMAD4. The clinical features have been mainly documented in childhood and comprise variable neurocognitive development, recognizable craniofacial features, a short stature with a pseudo-muscular build, hearing loss, thickened skin, joint limitations, diverse cardiovascular and airway manifestations, and increased fibrosis often following trauma or surgery. In contrast, adults with MS are underreported obscuring potential clinical variability. Here, we describe 24 adults with MS, including 17 diagnosed after the age of 18 years old, and we review the literature on adults with MS. Overall, our cohort shows a milder phenotype as well as lower mortality rates compared to what has been published in literature. Individuals with a codon 500 variant in SMAD4 present with a more pronounced neurodevelopmental and systemic phenotype. However, in contrast to the literature, we observe cardiovascular abnormalities in individuals with the p.(Arg496Cys) variant. In addition, we describe scoliosis as a new manifestation and we report fertility in two additional males with the p.(Arg496Cys). In conclusion, our study contributes novel insights into the clinical variability of MS and underscores the importance of variant-specific considerations, and we provide recommendations for the management of MS in adulthood.

Genetic blueprint of congenital muscular dystrophies with brain malformations in Egypt: A report of 11 families

Congenital muscular dystrophies (CMDs) are a group of rare muscle disorders characterized by early onset hypotonia and motor developmental delay associated with brain malformations with or without eye anomalies in the most severe cases. In this study, we aimed to uncover the genetic basis of severe CMD in Egypt and to determine the efficacy of whole exome sequencing (WES)-based genetic diagnosis in this population. We recruited twelve individuals from eleven families with a clinical diagnosis of CMD with brain malformations that fell into two groups: seven patients with suspected dystroglycanopathy and five patients with suspected merosin-deficient CMD. WES was analyzed by variant filtering using multiple approaches including splicing and copy number variant (CNV) analysis. We identified likely pathogenic variants in FKRP in two cases and variants in POMT1, POMK, and B3GALNT2 in three individuals. All individuals with merosin-deficient CMD had truncating variants in LAMA2. Further analysis in one of the two unsolved cases showed a homozygous protein-truncating variant in Feline Leukemia Virus subgroup C Receptor 1 (FLVCR1). FLVCR1 loss of function has never been previously reported. Yet, loss of function of its paralog, FLVCR2, causes lethal hydranencephaly-hydrocephaly syndrome (Fowler Syndrome) which should be considered in the differential diagnosis for dystroglycanopathy. Overall, we reached a diagnostic rate of 86% (6/7) for dystroglycanopathies and 100% (5/5) for merosinopathy. In conclusion, our results provide further evidence that WES is an important diagnostic method in CMD in developing countries to improve the diagnostic rate, management plan, and genetic counseling for these disorders.

Uniparental disomy for chromosome 1 with POMGNT1 splice-site variant causes muscle-eye-brain disease

POMGNT1, encoding protein O-mannose beta-1,2-N-acetylglucosaminyltransferase 1, is one of the genes responsible for dystroglycanopathy (DGP), which includes multiple phenotypes such as muscle-eye-brain disease (MEB), congenital muscular dystrophy with intellectual disability, and limb-girdle muscular dystrophy Here, we report a case of MEB that is the result of a homozygous variant of POMGNT1 that is revealed through uniparental disomy (UPD). An 8-month-old boy was admitted with mental and motor retardation, hypotonia, esotropia, early onset severe myopia, and structural brain abnormalities. A panel testing of genetic myopathy-related genes was used to identify a homozygous c.636C>T (p.Phe212Phe) variant in exon 7 of POMGNT1 in the patient, a heterozygous c.636C>T variant in the father, and the wild type in the mother. Quantitative polymerase chain reaction (q-PCR) revealed no abnormal copy numbers in exon 7. Trio-based whole-exome sequencing (trio-WES) revealed a possible paternal UPD on chromosome 1 of the patient. Chromosomal microarray analysis (CMA) revealed a 120,451 kb loss of heterozygosity (LOH) on 1p36.33-p11.2, encompassing POMGNT1, and a 99,319 kb loss of heterozygosity on 1q21.2-q44, which indicated UPD. Moreover, RNA sequencing (RNA-seq) verified that the c.636C>T variant was a splice-site variant, leading to skipping of exon 7 (p.Asp179Valfs*23). In conclusion, to the best of our knowledge, we present the first case of MEB caused by UPD, providing valuable insights into the genetic mechanisms underlying this condition.

Unique clinical presentations and follow-up outcomes from experience with congenital disorders of glycosylation: PMM2-PGM1-DPAGT1-MPI-POMT2-B3GALNT2-DPM1-SRD5A3-CDG

OBJECTIVES

Congenital Glycosylation Disorders (CDG) are a large group of inherited metabolic diseases with multi-organ involvement. Herein, we aimed to expand the clinical characteristics of patients with CDG based on our experience with diagnoses and follow-up of CDG patients from different subtypes.

METHODS

The clinical and laboratory findings from the last 15 years were reviewed retrospectively in Ege University Child Metabolism and Nutrition Department.

RESULTS

There were 8 (57.2 %) females and 6 (42.8 %) males. Diagnoses of the patients were PMM2-CDG (n=4), PGM1-CDG (n=2), DPAGT1-CDG (n=2), SRD5A3-CDG (n=2), MPI-CDG (n=1), POMT2-CDG (n=1), B3GALNT2-CDG (n=1), DPM1-CDG (n=1). The clinical findings of the patients were dysmorphia (85.7 %), developmental delay (85.7 %), intellectual disability (85.7 %), ocular abnormalities (64.2 %), skeletal malformations (64.2 %), failure to thrive (57.1 %), microcephaly (57.1 %), hepatomegaly (35.7 %), hearing loss (35.7 %), seizures (28.5 %), gastrointestinal symptoms (21.4 %), endocrine abnormalities (21.4 %), and cardiac abnormalities (7.1 %). Laboratory findings were abnormal TIEF (92.8 %), abnormal liver enzymes (64.2 %), decreased protein C (64.2 %), decreased antithrombin III (64.2 %), decreased protein S (42.8 %), hypogammaglobulinemia (35.7 %), cerebellar hypoplasia (28.5 %), CK elevation (7.1 %), and hypoglycemia (7.1 %).

CONCLUSIONS

This study contributes to the literature by sharing our ultra-rare DPM1-CDG case with less than 20 cases in the literature and expanding the clinical and molecular characteristics of other CDG patients. Hyperinsulinemic hypoglycemia, short stature, hypothyroidism, growth hormone deficiency, hypogammaglobulinemia, pericardial effusion, elevated CK, congenital myasthenia, and anorectal malformation were unique findings that were observed. Cerebello-ocular findings accompanying multi-organ involvement were an essential clue for a possible CDG.