Jeroen Breckpot

Deleterious genetic variants in NOTCH1 are a major contributor to the incidence of non-syndromic Tetralogy of Fallot

Aims Familial recurrence studies provide strong evidence for a genetic component to the predisposition to sporadic, non-syndromic Tetralogy of Fallot (TOF), the most common cyanotic congenital heart disease (CHD) phenotype. Rare genetic variants have been identified as important contributors to the risk of CHD, but relatively small numbers of TOF cases have been studied to date. Here, we use whole exome sequencing to assess the prevalence of rare, potentially deleterious variants in candidate genes previously associated with both syndromic and non-syndromic TOF, in the largest cohort of non-syndromic TOF patients reported to date. Methods & Results 829 non-syndromic TOF patients underwent whole exome sequencing. A systematic review of the literature was conducted which revealed 77 genes in which mutations had been reported in patients with TOF. The presence of rare, deleterious variants in the 77 candidate genes was determined, defined by a minor allele frequency of ≤ 0.001 and scaled combined annotation-dependent depletion (CADD) score of ≥ 20. We found a clustering of heterozygous rare, deleterious variants in NOTCH1 (P=1.89E-15), DOCK6 (P=2.93E-07), MYOM2 (P= 7.35E-05), TTC37 (P=0.016), MESP1 (P=0.024) and TBX1 (P=0.039), after correcting for multiple testing. NOTCH1 was most frequently found to harbour deleterious variants. Changes were observed in 49 patients (6%; 95% confidence interval [CI]: 4.5% - 7.8%) and included six truncating/frameshift variants and forty missense variants. Sanger sequencing of the unaffected parents of thirteen cases identified five de novo variants. Variants were not confined to a single functional domain of the NOTCH1 protein but significant clustering of variants was evident in the EGF-like repeats (P=0.018). Three NOTCH1 missense variants (p.G200R, p.C607Y and de novo p.N1875S) were subjected to functional evaluation and showed a reduction in Jagged1 ligand-induced NOTCH signalling. p.C607Y, which exhibited the most significant reduction in signalling, also perturbed S1 cleavage of the NOTCH1 receptor in the Golgi. Conclusion The NOTCH1 locus is a frequent site of genetic variants predisposing to non-syndromic TOF with 6% of patients exhibiting rare, deleterious variants. Our data supports the polygenic origin of TOF and suggests larger studies may identify additional loci.

Expanding the phenotype of metabolic cutis laxa with an additional disorder of N-linked protein glycosylation

Genetic syndromes associated with cutis laxa (CL) and wrinkled skin are multisystem disorders with progeroid features, including sagging, lax and wrinkled skin [1, 2]. Metabolic CL is genetically heterogeneous. We previously reported on the frequently overlapping clinical phenotypes, including X-linked and autosomal recessive forms [2]. However, recently new forms of CL have been described. “Metabolic” CL is related to different inborn errors of metabolism; the historic example is the X-linked defect in ATP7A (MIM 309400). Autosomal recessive metabolic CL types are ARCL2 and ARCL3. ARCL2 patients present with a characteristic face, skeletal and joint abnormalities, developmental and growth delay due to mutations in different genes, including ATP6V0A2 (MIM 219200, 278250), RIN2 (MIM 613075), COG7(MIM 608779), GORAB (MIM 231070), and PYCR1 (MIM 612940, 614438) [2–4]. These encode endosomal and Golgi proteins (ARCL2A), and affect trafficking and glycosylation, except for PYCR1, which is involved in mitochondrial proline synthesis (ARCL2B). ARCL3 patients have parchment-like, progeroid skin, cataracts, corneal clouding, and significant neurologic disease [5], caused by mutations in PYCR1 or ALDH18A1 (MIM 616603, 219150), also involved in mitochondrial proline synthesis [2]. Additional inborn errors can also be associated with CL without a clear designation to ARCL2 or ARCL3; Transaldolase deficiency (TALDO MIM 606003) and Lenz-Majewski syndrome (MIM 151050) and Cantu syndrome (MIM 239850). ATP6V0A2-CDG related CL has been described both with normal elastin histology (wrinkly skin syndrome MIM 278250) and abnormal elastin histology (ARCL2A MIM 219200). COG7-CDG is another CDG with CL and normal elastin morphology. Recently, novel metabolic CL syndromes were added to the growing list of ARCL. Their clinical presentation highly overlaps with the phenotypic spectrum of ARCL2A [6, 7] and ARCL2B [8]. Mutations in ATP6V1A (MIM 617403) and ATP6V1E1 (MIM 617402), two components of the VATPase complex, were shown to cause ARCL2A, and a very similar phenotype to that seen in ATP6V0A2-CDG [7]. They have a type II pattern on transferrin isoelectric focusing (TIEF) similar to defects involving the V-ATPase complex in the Golgi, affecting glycosylation [3, 7]. In another new ARCL, lactic acidemia is the diagnostic clue for mitochondrial ECHS1 (MIM 616277) [8] deficiency. Here we report on the previously unreported finding of CL due to a hemizygous mutation in the gene ATP6AP1 (MIM 300972), a component of the V-ATPase complex that was recently described to cause an X-linked N-glycosylation disorder with liver disease [9]. A male patient was born at term (birth weight 3.66 kg (P50), length 51 cm (P10), and head-circumference 35 cm (P25)). He had CL with excess skin in the neck, axilla and groin and unilateral cryptorchidism (Fig. 1). At 2 weeks of age he had a urinary tract infection with sepsis due to Escherichia Coli. There were no underlying structural abnormalities of the urinary tract. At 2 months he developed conjugated jaundice (bilirubin direct/total 4.49/13.77 mg/d, AST 401 IU/L, ALT 73 IU/L, gammaGT and alkaline phosphatase were normal, ceruloplasmin was 0.03 mg/dL (normal range: 0.22–0.58 g/L). Stools were pigmented. Liver ultrasound showed normal bile ducts, hyperechogenic liver parenchyma, normal liver size but enlarged spleen (+3.7 SD). Urinary polyols showed an increased galactitol * Peter Witters peter.witters@uzleuven.be

Phenotypic spectrum of Au–Kline syndrome: a report of six new cases and review of the literature

Au–Kline syndrome (AKS, OMIM 616580) is a multiple malformation syndrome, first reported in 2015, associated with intellectual disability. AKS has been associated with de novo loss-of-function variants in HNRNPK (heterogeneous ribonucleoprotein K), and to date, only four of these patients have been described in the literature. Recently, an additional patient with a missense variant in HNRNPK was also reported. These patients have striking facial dysmorphic features, including long palpebral fissures, ptosis, deeply grooved tongue, broad nose, and down-turned mouth. Patients frequently also have skeletal and connective tissue anomalies, craniosynostosis, congenital heart malformations, and renal anomalies. In this report, we describe six new patients and review the clinical information on all reported AKS patients, further delineating the phenotype of AKS. There are now a total of 9 patients with de novo loss-of-function variants in HNRNPK, one individual with a de novo missense variant in addition to 3 patients with de novo deletions of 9q21.32 that encompass HNRNPK. While there is considerable overlap between AKS and Kabuki syndrome (KS), these additional patients demonstrate that AKS does have a distinct facial gestalt and phenotype that can be differentiated from KS. This growing AKS patient cohort also informs an emerging approach to management and health surveillance for these patients.

Abnormal lung features on prenatal ultrasound and postnatal outcome

the patient received decreasing doses of oral propranolol. During this process and even after the discontinuation of the drugs, the symptoms did not aggravate. The symptoms have not recurred 2 months after the discontinuation of the drugs. Conclusion: We report that subglottic haemangioma accompanied by respiratory distress and failure in an infant was successfully treated by oral prednisolone followed by treatment with inhalation of nebulised budesonide and oral propranolol.