A novel phenotype in N-glycosylation disorders: Gillessen-Kaesbach-Nishimura skeletal dysplasia due to pathogenic variants in ALG9.

A rare lethal autosomal recessive syndrome with skeletal dysplasia, polycystic kidneys and multiple malformations was first described by Gillessen-Kaesbach et al and subsequently by Nishimura et al. The skeletal features uniformly comprise a round pelvis, mesomelic shortening of the upper limbs and defective ossification of the cervical spine. We studied two unrelated families including three affected fetuses with Gillessen-Kaesbach-Nishimura syndrome using whole-exome and Sanger sequencing, comparative genome hybridization and homozygosity mapping. All affected patients were shown to have a novel homozygous splice variant NM_024740.2: c.1173+2T>A in the ALG9 gene, encoding alpha-1,2-mannosyltransferase, involved in the formation of the lipid-linked oligosaccharide precursor of N-glycosylation. RNA analysis demonstrated skipping of exon 10, leading to shorter RNA. Mass spectrometric analysis showed an increase in monoglycosylated transferrin as compared with control tissues, confirming that this is a congenital disorder of glycosylation (CDG). Only three liveborn children with ALG9-CDG have been previously reported, all with missense variants. All three suffered from intellectual disability, muscular hypotonia, microcephaly and renal cysts, but none had skeletal dysplasia. Our study shows that some pathogenic variants in ALG9 can present as a lethal skeletal dysplasia with visceral malformations as the most severe phenotype. The skeletal features overlap with that previously reported for ALG3- and ALG12-CDG, suggesting that this subset of glycosylation disorders constitutes a new diagnostic group of skeletal dysplasias.

Autosomal dominant brachyolmia in a large Swedish family: phenotypic spectrum and natural course.

Autosomal dominant brachyolmia (Type 3, OMIM #113500) belongs to a group of skeletal dysplasias caused by mutations in the transient receptor potential cation channel, subfamily V, member 4 (TRPV4) gene, encoding a Ca++-permeable, non-selective cation channel. The disorder is characterized by disproportionate short stature with short trunk, scoliosis and platyspondyly. The phenotypic variability and long-term natural course remain inadequately characterized. The purpose of this study was to describe a large Swedish family with brachyolmia type 3 due to a heterozygous TRPV4 mutation c.1847G>A (p.R616Q) in 11 individuals. The mutation has previously been detected in another family with autosomal dominant brachyolmia [Rock et al., 2008]. Review of hospital records and patient assessments indicated that clinical symptoms of brachyolmia became evident by school age with chronic pain in the spine and hips; radiographic changes were evident earlier. Growth was not affected during early childhood but deteriorated with age in some patients due to increasing spinal involvement. Affected individuals had a wide range of subjective symptoms with chronic pain in the extremities and the spine, and paresthesias. Our findings indicate that autosomal dominant brachyolmia may be associated with significant long-term morbidity, as seen in this family.

Different mutations in PDE4D associated with developmental disorders with mirror phenotypes.

BACKGROUND: Point mutations in PDE4D have been recently linked to acrodysostosis, an autosomal dominant disorder with skeletal dysplasia, severe brachydactyly, midfacial hypoplasia and intellectual disability. The purpose of the present study was to investigate clinical and cellular implications of different types of mutations in the PDE4D gene. METHODS: We studied five acrodysostosis patients and three patients with gene dose imbalances involving PDE4D clinically and by whole exome sequencing, Sanger sequencing and array comparative hybridisation. To evaluate the functional consequences of the PDE4D changes, we used overexpression of mutated human PDE4D message and morpholino-based suppression of pde4d in zebrafish. RESULTS: We identified three novel and two previously described PDE4D point mutations in the acrodysostosis patients and two deletions and one duplication involving PDE4D in three patients suffering from an intellectual disability syndrome with low body mass index, long fingers, toes and arms, prominent nose and small chin. When comparing symptoms in patients with missense mutations and gene dose imbalances involving PDE4D, a mirror phenotype was observed. By comparing overexpression of human mutated transcripts with pde4d knockdown in zebrafish embryos, we could successfully assay the pathogenicity of the mutations. CONCLUSIONS: Our findings indicate that haploinsufficiency of PDE4D results in a novel intellectual disability syndrome, the 5q12.1-haploinsufficiency syndrome, with several opposing features compared with acrodysostosis that is caused by dominant negative mutations. In addition, our results expand the spectrum of PDE4D mutations underlying acrodysostosis and indicate that, in contrast to previous reports, patients with PDE4D mutations may have significant hormone resistance with consequent endocrine abnormalities.

The phenotype range of achondrogenesis 1A.

Achondrogenesis 1A (ACG1A; OMIM 200600) is an autosomal recessive perinatally lethal skeletal dysplasia comprising intrauterine growth failure, micromelia, minor facial anomalies, deficient ossification of the skull, absent or extremely defective spinal ossification, short beaded ribs, and short deformed long bones with a stellate appearance. ACG1A is caused by mutations in the TRIP11 gene, resulting in deficiency of the Golgi microtubule associated protein 210. In this study we describe dizygotic twins with a clinical and radiological phenotype of ACG1A who were homozygous for a novel nonsense mutation in the TRIP11 gene. In addition, another patient with a milder manifestation, not readily distinguishable from those of other lethal skeletal dysplasias, was found to be a compound heterozygote for a nonsense mutation and a deletion of the 3' end of the TRIP11 gene. We conclude that mutations of the TRIP11 gene may encompass a wider phenotypic range than previously recognized.

Clinical and radiographic features of the autosomal recessive form of brachyolmia caused by PAPSS2 mutations.

Brachyolmia is a heterogeneous skeletal dysplasia characterized by generalized platyspondyly without significant long-bone abnormalities. Based on the mode of inheritance and radiographic features, at least three types of brachyolmia have been postulated. We recently identified an autosomal recessive form of brachyolmia that is caused by loss-of-function mutations of PAPSS2, the gene encoding PAPS (3'-phosphoadenosine 5'-phosphosulfate) synthase 2. To understand brachyolmia caused by PAPSS2 mutations (PAPSS2-brachyolmia), we extended our PAPSS2 mutation analysis to 13 patients from 10 families and identified homozygous or compound heterozygous mutations in all. Nine different mutations were found: three splice donor-site mutations, three missense mutations, and three insertion or deletion mutations within coding regions. In vitro enzyme assays showed that the missense mutations were also loss-of-function mutations. Phenotypic characteristics of PAPSS2-brachyolmia include short-trunk short stature, normal intelligence and facies, spinal deformity, and broad proximal interphalangeal joints. Radiographic features include platyspondyly with rectangular vertebral bodies and irregular end plates, broad ilia, metaphyseal changes of the proximal femur, including short femoral neck and striation, and dysplasia of the short tubular bones. PAPSS2-brachyolmia includes phenotypes of the conventional clinical concept of brachyolmia, the Hobaek and Toledo types, and is associated with abnormal androgen metabolism.

FAM111A mutations result in hypoparathyroidism and impaired skeletal development.

Kenny-Caffey syndrome (KCS) and the similar but more severe osteocraniostenosis (OCS) are genetic conditions characterized by impaired skeletal development with small and dense bones, short stature, and primary hypoparathyroidism with hypocalcemia. We studied five individuals with KCS and five with OCS and found that all of them had heterozygous mutations in FAM111A. One mutation was identified in four unrelated individuals with KCS, and another one was identified in two unrelated individuals with OCS; all occurred de novo. Thus, OCS and KCS are allelic disorders of different severity. FAM111A codes for a 611 amino acid protein with homology to trypsin-like peptidases. Although FAM111A has been found to bind to the large T-antigen of SV40 and restrict viral replication, its native function is unknown. Molecular modeling of FAM111A shows that residues affected by KCS and OCS mutations do not map close to the active site but are clustered on a segment of the protein and are at, or close to, its outer surface, suggesting that the pathogenesis involves the interaction with as yet unidentified partner proteins rather than impaired catalysis. FAM111A appears to be crucial to a pathway that governs parathyroid hormone production, calcium homeostasis, and skeletal development and growth.

Extending the phenotype of lethal skeletal dysplasia type al Gazali.

In this study, we describe the clinical and radiological phenotype of two patients with a rare skeletal dysplasia type al Gazali. The phenotype is characterized by brachycephaly, flat face, hypertelorism, low-set ears, hypertrichosis, hypoplastic thorax, as well as short extremities with brachydactyly. Further characteristics are severe fetal hydrops, radiologic signs of increased bone density and short, poorly modeled tubular bones with wide diaphysis and smooth, rounded metaphyses. Cortical bones as well as vertebral endplates are thick and the skull is sclerotic with prominent parietal bones and a large anterior fontanel. Our cases suggest that skeletal dysplasia type al Gazali is a lethal condition and provide further evidence that it is inherited in an autosomal recessive manner. Both morphological and radiological features of these patients are very similar, which together with the previous report may indicate the presence of a new clinical entity in the group of skeletal dysplasias with increased bone density and metaphyseal and diaphyseal involvement. Surprisingly, histological analysis of the bone tissue and the growth plate shows completely normal structure, which suggests that the skeletal dysplasia type al Gazali is a systemic disorder resulting in increased bone density and restricted growth of the skeleton.