Thurman, Sarah

ABSTRACT The cohesin complex, composed of SMC1, SMC3, RAD21, and STAG1/STAG2, is essential for chromosome cohesion, DNA repair, and transcriptional regulation. Pathogenic variants in cohesin components cause cohesinopathies. The classical characteristics of cohesinopathies include developmental delay (DD), intellectual disability (ID), feeding difficulties, hypotonia, short stature, hearing loss, and dysmorphic features. Here, we present a 5‐year‐old boy with classical cohesinopathy features, including DD/ID and feeding difficulties, along with non‐classical features such as hypoglycemia, recurrent fever, and immunodeficiency. Trio exome sequencing identified a novel de novo missense variant of uncertain significance (NM_005862.3:c.643G>A(p.Val215Ile)) in the STAG1 gene. The variant localizes to the RAD21 interaction interface, and molecular dynamics (MD) simulations revealed conformational changes comparable to other STAG1 variants reported as likely pathogenic in patients, supporting a deleterious effect which may disrupt the STAG1‐RAD21 interaction interface. This case expands the phenotypic and molecular spectrum of STAG1‐related cohesinopathy and advances our understanding of the disease mechanism.

ABSTRACT Post‐translational modifications, such as glycosylation and phosphorylation, play a critical role in protein trafficking, interactions, and stability. Disruptions in these pathways can lead to glycosylphosphatidylinositol (GPI) deficiencies, which present with a spectrum of clinical features, including congenital anomalies, dysmorphic features, developmental delay, hypotonia, and epilepsy. Biallelic variants in PIGV , a key mannosyltransferase in GPI biosynthesis, cause Hyperphosphatasia with Impaired Intellectual Development Syndrome 1 (HPMRS1), a rare disorder characterized by hyperphosphatasia, seizures, developmental delay, hypotonia, abnormal MRI findings, and distinct facial dysmorphisms. Fewer than 30 cases have been reported to date. We conducted a case study and literature review; with clinical data obtained from medical records. A 2‐year‐old female presented with developmental delay, myoclonic epilepsy, hypotonia, and mild facial dysmorphism. Laboratory results showed elevated alkaline phosphatase (899 U/L) and low pyridoxal 5′‐phosphate levels in cerebrospinal fluid (CSF). Brain MRI revealed diffuse cerebral volume loss and ventriculomegaly. Trio genome sequencing identified two PIGV variants: c.1415T>C‐p.(Leu472Pro) and c.524T>C‐p.(Leu175Pro). Functional studies using PIGV ‐knockout HEK293 cells transfected with wild‐type or mutant PIGV constructs demonstrated reduced GPI‐anchored protein (GPI‐AP) expression under weaker promoters, indicating impaired enzymatic activity. We report two novel PIGV variants associated with HPMRS1, emphasizing the value of functional assays in variant interpretation. Our findings also highlight the diagnostic relevance of alkaline phosphatase measurement in patients with refractory seizures.

Purpose To document the association of CAD-related disorder (EIEE-50) with cortical visual impairment. Observations An 8-month-old Caucasian boy with whole genome sequencing confirming 2 variants in the gene CAD, who presented with severe seizures, microcephaly, hyperreflexia, hypotonia, anemia, and severe cortical visual impairment. Magnetic resonance imaging (MRI) of the brain noted thickened cortical gray matter along the right calcarine fissure as well as changes suggesting malformation of cortical development. Empiric uridine monophosphate supplementation has significantly improved seizure activity, hypotonia, and development and has led to resolution of anemia. Conclusions and Importance CAD-related disorder is treatable and may affect visual cortical development causing severe secondary cortical visual impairment, a newly described clinical manifestation.