Characterizing a Cohort of α-Thalassemia Couples Collected During Screening for Hemoglobinopathies: 14 Years of an Iranian Experience

Our study aimed to determine the number of couples with normal hemoglobin (Hb) electrophoresis and low-borderline hematological values, which may come up with a clinically critical status in their offspring. The number of couples at risk for severe α-thalassemia (α-thal) needed to be estimated before recommending genetic counseling and prenatal diagnosis (PND). During the past 14 years, from at least 7000 referrals, 754 couples were investigated for α-thal by direct mutation detection methods followed by reverse strip assay and α-globin gene sequencing for inconclusive cases. Detection of silent β-thalassemia (β-thal) mutations was done in suspected cases by complete β-globin gene sequencing. We were able to provide a molecular diagnosis in 87.3% (658/754) of couples. A total of 9.1% (60/658) may have a clinically significant hemoglobinopathy in their offspring. Significant conditions included hydrops fetalis (20.0%; 12/60), certain Hb H (β4) genotypes (78.3%; 47/60) and β-thal intermedia (β-TI) (1.7%; 1/60). The diagnostic flowchart for couples with microcytic hypochromic anemia in countries with a high prevalence of hemoglobinopathies should include α and β gene sequencing. As our results indicate, every nine out of 100 of these couples will face significant hemoglobinopathies and every two out of 100 can carry Hb Bart’s (γ4) hydrops fetalis in their pregnancies. For such cases, PND should be utilized to allow the carrier couples to decide whether or not to abort the fetus.     

SLC2A2 mutations can cause neonatal diabetes, suggesting GLUT2 may have a role in human insulin secretion

Aims  

The gene SLC2A2 encodes GLUT2, which is found predominantly in pancreas, liver, kidney and intestine. In mice, GLUT2 is the major glucose transporter into pancreatic beta cells, and biallelic Slc2a2 inactivation causes lethal neonatal diabetes. The role of GLUT2 in human beta cells is controversial, and biallelic SLC2A2 mutations cause Fanconi–Bickel syndrome (FBS), with diabetes rarely reported. We investigated the potential role of GLUT2 in the neonatal period by testing whether SLC2A2 mutations can present with neonatal diabetes before the clinical features of FBS appear.     

The prevalence and phenotypic range associated with biallelic PKDCC variants

PKDCC encodes a component of Hedgehog signalling required for normal chondrogenesis and skeletal development. Although biallelic PKDCC variants have been implicated in rhizomelic shortening of limbs with variable dysmorphic features, this association was based on just two patients. In this study, data from the 100 000 Genomes Project was used in conjunction with exome sequencing and panel-testing results accessed via international collaboration to assemble a cohort of eight individuals from seven independent families with biallelic PKDCC variants. The allelic series included six frameshifts, a previously described splice-donor site variant and a likely pathogenic missense variant observed in two families that was supported by in silico structural modelling. Database queries suggested that the prevalence of this condition is between 1 of 127 and 1 of 721 in clinical cohorts with skeletal dysplasia of unknown aetiology. Clinical assessments, combined with data from previously published cases, indicate a predominantly upper limb involvement. Micrognathia, hypertelorism and hearing loss appear to be commonly co-occurring features. In conclusion, this study strengthens the link between biallelic inactivation of PKDCC and rhizomelic limb-shortening and will enable clinical testing laboratories to better interpret variants in this gene.     

Double de novo mutations of ELA2 in cyclic and severe congenital neutropenia

Heterozygous mutations of ELA2, encoding the protease neutrophil elastase (NE), cause either autosomal dominant cyclic neutropenia or severe congenital neutropenia (SCN). Three hypotheses have been proposed for how allelic mutations produce these different disorders: 1) disruption of proteolytic activity; 2) mislocalization of the protein; or 3) destabilization of the protein resulting in induction of the unfolded protein response. As with other dominant diseases with reduced reproductive fitness, sporadic cases can result from new mutations not inherited from either parent. Here we report an exceptional genetic phenomenon in which both a cyclic neutropenia patient and an SCN patient each possess two new ELA2 mutations. Because of the rarity of the phenomenon, we investigated the origins of the mutations and found that both arise nonmosaically and in cis from the paternally-inherited allele. Moreover, these cases offer a unique opportunity to investigate molecular pathways distinguishing these two forms of hereditary neutropenia. We have characterized the mutants separately and in combination, with respect to their effects on proteolysis, subcellular trafficking, and induction of the unfolded protein response. Each pair of mutations acts more or less additively to produce equivalent net effects on reducing proteolytic activity and induction of the unfolded protein response, yet each has different and somewhat opposing effects on disturbing subcellular localization, thus offering support for a role for protein mistrafficking as a disease mechanism.     

Improved diagnostic yield of neuromuscular disorders applying clinical exome sequencing in patients arising from a consanguineous population

Neuromuscular diseases (NMDs) include a broad range of disorders affecting muscles, nerves and neuromuscular junctions. Their overlapping phenotypes and heterogeneous genetic nature have created challenges in diagnosis which calls for the implementation of massive parallel sequencing as a candidate strategy to increase the diagnostic yield. In this study, total of 45 patients, mostly offspring of consanguineous marriages were examined using whole exome sequencing. Data analysis was performed to identify the most probable pathogenic rare variants in known NMD genes which led to identification of causal variants for 33 out of 45 patients (73.3%) in the following known genes: CAPN3, Col6A1, Col6A3, DMD, DYSF, FHL1, GJB1, ISPD, LAMA2, LMNA, PLEC1, RYR1, SGCA, SGCB, SYNE1, TNNT1 and 22 novel pathogenic variants were detected. Today, the advantage of whole exome sequencing in clinical diagnostic strategies of heterogeneous disorders is clear. In this cohort, a diagnostic yield of 73.3% was achieved which is quite high compared to the overall reported diagnostic yield of 25% to 50%. This could be explained by the consanguineous background of these patients and is another strong advantage of offering clinical exome sequencing in diagnostic laboratories, especially in populations with high rate of consanguinity.     

An/micr-Ophthalmia, Cleft Lip/Palate, and Short Limbs: A New Syndrome Simulating a Short Rib Syndrome

We report on a male infant born at 38 weeks of gestation with hydrocephalus, right anophthalmia, left microphthalmia, cleft palate, midline cleft of lip, and microphallus. Autopsy showed pulmonary bronchial lymphangiectasia, hepatic periportal fibrosis, adrenal agenesis, ventricular septal defect, aortic stenosis, and undescended testes. The radiographic findings include short limbs and mild shortness of ribs. Karyotype with high-resolution banding was normal (46,XY). The combination of anomalies in this case could suggest a ciliopathy and may represent a new entity similar to that described by Cideciyan et al. [ 1 ].     

Identification of disease-causing variants in the EXOSC gene family underlying autosomal recessive intellectual disability in Iranian families

Neurodevelopmental delay and intellectual disability (ID) can arise from numerous genetic defects. To date, variants in the EXOSC gene family have been associated with such disorders. Using next-generation sequencing (NGS), known and novel variants in this gene family causing autosomal recessive ID (ARID) have been identified in five Iranian families. By collecting clinical information on these families and comparing their phenotypes with previously reported patients, we further describe the clinical variability of ARID resulting from alterations in the EXOSC gene family, and emphasize the role of RNA processing dysregulation in ARID.