Prenatal diagnosis of Desbuquois dysplasia type 1 by whole exome sequencing before the occurrence of specific ultrasound signs

Prenatal and neonatal phenotype of Larsen of La Réunion Island syndrome (B4GALT7-linkeropathy)

Larsen of La Réunion Island syndrome (LRS) is an autosomal recessive condition associated with multiple large joint dislocations, clubfeet, severe dwarfism, and distinctive facial features. LRS is caused by a recurrent homozygous variant in B4GALT7 gene with a founder effect in La Réunion population. Proteoglycans (PG) that are a major component of the extracellular matrix, are composed of a core protein connected to a glycosaminoglycans side chain via a tetrasaccharide linker region. B4GALT7 encodes galactosyltransferase I, one of the enzymes involved in the biosynthesis of the linker region. Conditions caused by pathogenic biallelic variants in genes implicated in the synthesis of the tetrasaccharide linker of PG are known as linkeropathies. Prenatal features are rarely described in this group of chondrodysplasias. We present a series of 12 unpublished patients having LRS and describe the perinatal phenotype. All the patients had a prenatal growth restriction with brevity of limbs. The other features revealed by ultrasounds were increased nuchal translucency at 10-12 weeks of gestation (50 %), feet abnormalities (clubfeet or metatarsus varus) (25 %), dislocation affecting at least one large joint (elbow, knee, wrist) (25 %). Bilateral bowing of femora was noted for two fetuses. Fibular hypertrophy was noted for one fetus. Prenatal helical computed tomography (CT) performed in three pregnancies showed additional data such as bowing of the forearm bones, proximal radio-ulnar synostosis, or dislocation of large joints. Prenatal sonographic and helical CT findings led to the prenatal diagnosis of LRS in four patients. We confirm that the neonatal clinical picture of LRS has an important overlap with that reported in patients with B4GALT7 deficiency outside La Réunion Island and other linkeropathies. The core of the phenotypic spectrum combines low birth height, micromelia, hypermobility, dislocation of at least one large joint, facial features with prominent eyes, microstomia, depressed nasal bridge, and midface hypoplasia. Other clinical features include clubfeet (33%), bifid thumb in one patient, and cardiac abnormalities in two patients. Radiological findings include radio-ulnar synostosis (75%), metaphyseal flaring, precocious carpal ossification, and a Swedish key appearance of the proximal femora. Finally, we also report radiological features rarely described in B4GALT7-linkeropathies, including bowing of the femora and fibular hypertrophy. Our results confirm the phenotypic continuum of LRS within linkeropathies with some additional findings, including a high frequency of clubfeet usually described in B3GALT6-linkeropathies, the presence of congenital heart diseases usually described in B3GAT3-linkeropathies, and a high frequency of metaphyseal flaring usually reported in B3GALT6 or XITLT1-linkeropathies. This is the first study that describes the perinatal phenotype in a cohort of patients with LRS. This study can help improve the prenatal diagnosis of the linkeropathies and add this group of conditions to the differential diagnosis of chondrodysplasias with multiple dislocations. In view of the founder effect for LRS in La Réunion Island, this disease should be suspected in fetuses with growth restriction and micromelia. Thus in case of LOH which include B4GALT7 identified in SNP-array, we recommend performing a targeted Sanger sequencing for the recurrent mutation c.808C > T; p. (Arg270Cys).

Antenatal Phenotype of Desbuquois Dysplasia

Desbuquois dysplasia (DBQD) is an uncommon, autosomal recessive disorder with multiple joint dislocations. It is caused by pathogenic variants in CANT1 (calcium-activated nucleotidase 1) [NM_001159773.2]. This study adds to the scant data of nine reported antenatal phenotypes of DBQD. The present paper describes two unrelated consanguineous families with antenatal features of lethal skeletal dysplasia. The defining radiological changes were identified in only one patient who presented in the late second and third trimesters. Solo exome sequencing was performed and two previously reported homozygous variants c.896C>T (p.Pro299Leu) in patient 1 and c.902_906dup (p.Ser303fs*20) in patient 2 were identified. This study highlights the fetal presentations in DBQD and adds to its phenotypic spectrum. A complete clinical workup, including fetal autopsy and radiographs is essential to confirm the diagnosis of lethal skeletal dysplasia. Molecular diagnosis remains the diagnostic modality to define the causative variant. A definitive diagnosis is essential to inform management and offer reproductive care.

Fetal presentation of chondrodysplasia with joint dislocations, GPAPP type, caused by novel biallelic IMPAD1 variants

Biallelic IMPAD1 pathogenic variants leads to deficiency of GPAPP (Golgi 3-prime phosphoadenosine 5-prime phosphate 3-prime phosphatase) protein and clinically causes chondrodysplasia, which is characterized by short stature with short limbs, craniofacial malformations, cleft palate, hand and foot anomalies, and various radiographic skeletal manifestations. Here we describe prenatal presentation of GPAPP deficiency caused by novel biallelic pathogenic variants, 2 base pair duplication in exon 2 of IMAPD1 gene in a patient of Asian-Indian origin. Further we report on diagnostic clues of prenatal presentation of GPAPP deficiency through ultrasonography, fetal MRI, and postmortem findings. We also provide evidence of pathophysiology of underlying GPAPP deficiency in the form of disorganization and dysplastic chondrocytes and reduced sulfation of glycoproteins through histopathology of cartilage similar to that described in mice IMPAD1 homozygous mutant model.

First Report of Two Egyptian Patients with Desbuquois Dysplasia due to Homozygous CANT1 Mutations

Desbuquois dysplasia type 1 (DBQD1) is a very rare skeletal dysplasia characterized by growth retardation, short stature, distinct hand features, and a characteristic radiological monkey wrench appearance at the proximal femur. We report on 2unrelated Egyptian patients having the characteristic features of DBQD1 with different expressivity. Patient 1 presented at the age of 45 days with respiratory distress, short limbs, faltering growth, and distinctive facies while patient 2 presented at 5 years of age with short stature and hypospadias. The 2 patients shared radiological features suggestive of DBQD1. Whole-exome sequencing revealed a homozygous frameshift mutation in the CANT1 gene (NM_001159772.1:c.277_278delCT; p.Leu93ValfsTer89) in patient 1 and a homozygous missense mutation (NM_138793.4:c.898C>T; p.Arg300Cys) in patient 2. Phenotypic variability and variable expressivity of DBQD was evident in our patients. Hypoplastic scrotum and hypospadias were additional unreported associated findings, thus expanding the phenotypic spectrum of the disorder. We reviewed the main features of skeletal dysplasias exhibiting similar radiological manifestations for differential diagnosis. We suggest that the variable severity in both patients could be due to the nature of the CANT1 gene mutations which necessitates the molecular study of more cases for phenotype-genotype correlations.