Klee, Eric

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.

AbstractUBE2A deficiency, that is, intellectual disability (ID) Nascimento type (MIM 300860), is an X‐linked syndrome characterized by developmental delay, moderate to severe ID, seizures, dysmorphisms, skin anomalies, and urogenital malformations. Forty affected subjects have been reported thus far, with 31 cases having intragenic UBE2A variants. Here, we report on additional eight affected subjects from seven unrelated families who were found to be hemizygous for previously unreported UBE2A missense variants (p.Glu62Lys, p.Arg95Cys, p.Thr99Ala, and p.Arg135Trp) or small in‐frame deletions (p.Val81_Ala83del, and p.Asp101del). A wide phenotypic spectrum was documented in these subjects, ranging from moderate ID associated with mild dysmorphisms to severe features including congenital heart defects (CHD), severe cognitive impairment, and pineal gland tumors. Four variants affected residues (Glu62, Arg95, Thr99 and Asp101) that contribute to stabilizing the structure of the E3 binding domain. The three‐residue in‐frame deletion, p.Val81_Ala83del, resulted from aberrant processing of the transcript. This variant and p.Arg135Trp mapped to regions of the protein located far from the E3 binding region, and caused variably accelerated protein degradation. By reviewing available clinical information, we revise the clinical and molecular profile of the disorder and document genotype‐phenotype correlations. Pineal gland cysts/tumors, CHD and hypogammaglobulinemia emerge as recurrent features.

ABSTRACT Inactivating mutations of the ENPP1 gene are associated with generalized arterial calcification of infancy (GACI) and less often autosomal-recessive hypophosphatemic rickets type 2 (ARHR2). We aimed to investigate the spectrum of phenotypes in a family with monoallelic and biallelic mutations of ENPP1 after identification through whole exome sequencing of a 54-year-old female with biallelic mutation of ENPP1, c.323G > T; p.Cys108Phe and c.1441C > T; p.Arg481Trp. Including the proband, 2 subjects had biallelic mutations, 5 had monoallelic mutations, and 2 had no mutation of ENPP1. The maternal mutation, a known pathogenic variant associated with GACI, was found in 3 subjects with monoallelic mutations, while the paternal mutation, which was not previously reported, was present in 2 subjects with monoallelic mutations. Both subjects with biallelic mutations had bowing of bilateral femurs, periarticular mineral deposition, normocalcemic primary hyperparathyroidism with multigland parathyroidectomy, increased carotid intima-media thickness, and enthesopathy was also noted in one subject. Intact FGF23 was elevated in both subjects with biallelic mutations, while C-terminal FGF23 was only elevated in one and PPi was reduced in one. Subjects with monoallelic mutations did not have periarticular calcifications or bone deformities. To conclude, patients with biallelic GACI causing mutations can survive well into adulthood, and despite the same biallelic ENPP1 pathogenic variants, clinical and biochemical manifestations can significantly differ, and include enthesopathy and primary hyperparathyroidism, which have not been previously described. Although carriers of monoallelic ENPP1 variants appear unaffected by classic disease manifestations, there may be subtle biochemical and clinical findings that warrant further investigation. © 2019 American Society for Bone and Mineral Research.