Retrospective evaluation of clinical and molecular data of 148 cases of esophageal atresia.

Developmental abnormalities provide a unique opportunity to seek for the molecular mechanisms underlying human organogenesis. Esophageal development remains incompletely understood and elucidating causes for esophageal atresia (EA) in humans would contribute to achieve a better comprehension. Prenatal detection, syndromic classification, molecular diagnosis, and prognostic factors in EA are challenging. Some syndromes have been described to frequently include EA, such as CHARGE, EFTUD2-mandibulofacial dysostosis, Feingold syndrome, trisomy 18, and Fanconi anemia. However, no molecular diagnosis is made in most cases, including frequent associations, such as Vertebral-Anal-Cardiac-Tracheo-Esophageal-Renal-Limb defects (VACTERL). This study evaluates the clinical and genetic test results of 139 neonates and 9 fetuses followed-up at the Necker-Enfants Malades Hospital over a 10-years period. Overall, 52 cases were isolated EA (35%), and 96 were associated with other anomalies (65%). The latter group is divided into three subgroups: EA with a known genomic cause (9/148, 6%); EA with Vertebral-Anal-Cardiac-Tracheo-Esophageal-Renal-Limb defects (VACTERL) or VACTERL/Oculo-Auriculo-Vertebral Dysplasia (VACTERL/OAV) (22/148, 14%); EA with associated malformations including congenital heart defects, duodenal atresia, and diaphragmatic hernia without known associations or syndromes yet described (65/148, 44%). Altogether, the molecular diagnostic rate remains very low and may underlie frequent non-Mendelian genetic models.

Peri- and neonatal factors influencing mortality and morbidity 2 years after esophageal atresia primary repair: a single center retrospective study.

Long-term digestive, respiratory, and neurological morbidity is significant in children who have undergone surgery for esophageal atresia (EA), especially after staged repair for long-gap EA. Risk factors for morbidity after primary repair (non-long-gap populations) have been less documented. We investigated peri- and neonatal factors associated with unfavorable outcomes in children 2 years after primary esophageal anastomosis. This was a single-center retrospective study, based on neonatal, surgical, and pediatric records of children born between December 1, 2002, and December 31, 2018, and followed up to age 2 years. The primary endpoint was unfavorable outcome at 2 years of age, defined by death or survival with severe respiratory, digestive, or neurologic morbidity. Univariate analyses followed by logistic regression analyses were performed to identify the peri- and neonatal risk factors of unfavorable outcomes among survivors at discharge. A total of 150 neonates were included (mean birth weight 2520 ± 718 g, associated malformations 61%); at age 2, 45 (30%) had one or more severe morbidities and 11 had died during the neonatal stay and 2 after discharge (8.7% deaths). In multivariate analyses of the 139 survivors at discharge, duration of ventilatory support (invasive and non-invasive) for more than 8 days (OR 3.74; CI95% [1.68-8.60]; p = 0.001) and achievement of full oral feeding before hospital discharge (OR 0.20; CI95% [0.06-0.56]; p = 0.003) were independently associated with adverse outcome after adjustment for sex, preterm birth, associated heart defect, any surgical complication, and the occurrence of more than one nosocomial infections during the neonatal stay. CONCLUSIONS: Post-operative ventilation and feeding management strategies may represent an opportunity for quality-of-care improvement to positively impact long-term outcomes after primary esophageal atresia repair. WHAT IS KNOWN: • Children operated on for esophageal atresia experience long-term digestive, respiratory, and neurologic morbidity, especially after multiple-stage esophageal repair. • Exclusive oral feeding at discharge is associated with a decreased risk of medical complications in the first years of life, in studies including all types of esophageal atresia repair. Outcomes of children after primary repair (non-long gap populations) have been less documented. WHAT IS NEW: • In our retrospective cohort of children with one-stage esophageal atresia repair, ventilatory support for more than 8 days and inability to achieve full oral feeding before hospital discharge in the neonatal period were independently associated with adverse digestive, respiratory, and neurologic outcomes at 2 years in survivors. • Both these factors are potentially modifiable, representing an opportunity for quality-of-care improvement to positively impact long-term outcomes. These results might also help identify children at risk of unfavorable evolution, to customize a multi-disciplinary follow-up program.

Developmental outcome of children with Robin sequence treated with the current Paris protocol.

AIM: We aimed to investigate the developmental outcome of children with Robin sequence (RS) for whom continuous positive airway pressure was the main strategy to release upper airway obstruction. METHODS: We included children with isolated RS or RS associated with Stickler syndrome who were aged 15 months to 6 years. We used the French version of the Child Development Inventory and calculated the developmental quotient (DQ) for eight different domains and the global DQ (DQ-global). We searched for determinants of risk of delay. RESULTS: Of the 87 children, for 71%, the developmental evolution was within the norm (DQ-global ≥86 or ≥-1 SD), 29% were at high risk of delay (DQ-global <86 or <-1 SD), and only 3% were at very high risk of delay (DQ-global <70 or <-2 SD). The DQs for expressive language and language comprehension were lower in our study population than the general population, but an improvement was noticed with the children's growth. CONCLUSION: Risk of a developmental delay was not greater for children with the most severe respiratory phenotype than the others. Children whose mothers had low education levels were more at risk than the others.

[Creation of a tool to help assess eating disorders in young children]. / Création d'un outil d'aide à l'évaluation des troubles de l'oralité alimentaire du jeune enfant.

In order to optimize the care of young hospitalized children with eating disorders, the Orality group at the Necker-Enfants malades University Hospital in Paris has created a therapeutic education tool: the Fleur des sens. This flower which is to be colored at the end of the meal with the child has nine petals representing nine foods that make up the meal, which were initially difficult or even impossible for the young patient to eat. This tool participates in the educational diagnosis and then in the formative evaluation of the child. It is also useful for the parents' understanding of the disease, making the link between sensoriality and food orality.

MED13L loss-of-function variants in two patients with syndromic Pierre Robin sequence.

We report two unrelated patients with Pierre Robin sequence (PRS) and a strikingly similar combination of associated features. Whole exome sequencing was performed for both patients. No single gene containing likely pathogenic point mutations in both patients could be identified, but the finding of an essential splice site mutation in mediator complex subunit 13 like (MED13L) in one patient prompted the investigation of copy number variants in MED13L in the other, leading to the identification of an intragenic deletion. Disruption of MED13L, encoding a component of the Mediator complex, is increasingly recognized as the cause of an intellectual disability syndrome with associated facial dysmorphism. Our findings suggest that MED13L-related disorders are a possible differential diagnosis for syndromic PRS.

Hair analysis does not allow to discriminate between acute and chronic administrations of a drug in young children.

There are many differences between the hair from children and that of adult subjects, the hair being thinner, more porous with a different growth rate from the usual 1 cm/month observed in adults. In order to determine whether hair analysis could discriminate between chronic use and acute administration of a drug in children like in adults, we analyzed hair from 18 children aged between 1 day and 15 years in whom the administration of different drugs was known (single therapeutic administration or acute intoxication). A strand of hair was sampled within 1 to 45 days after treatment or intoxication. Analysis was conducted using LC/MS/MS. In the 10 youngest children, aged between 1 day and 29 months, the compounds administered in hospital or responsible for intoxication (lidocaine, ropivacaine, diazepam, midazolam, levetiracetam, morphine, ketamine, methadone, buprenorphine, THC, MDMA) were found in all segments of the hair independently of the time of sampling (1-45 days after ingestion). The concentrations detected were similar along the hair shaft, showing a radial diffusion and incorporation of the analytes in the hair of young children from the sebum. Concentrations could be very high when sampled shortly after administration (72 ng/mg for methadone, 75 ng/mg for MDMA after 3 days) and lower when sampling later (1.2 ng/mg for MDMA after 45 days). In these cases, hair analysis allowed to highlight the compounds responsible for intoxication even when they had disappeared from the blood or urine but should not be used to discriminate long-term exposure to a drug. In the eight remaining children aged from 34 months to 15 years, the drugs used in hospital (lidocaine, diazepam, morphine) or responsible for intoxication (THC, codeine, buprenorphine) were not found in any analyzed segments sampled 1 to 5 days after administration of the drugs, in agreement with the non-incorporation of the drugs from the sebum into the hair. For those children aged over 34 months, hair analysis allows to determine the chronic administration of a drug, like in adults.

Functional assessment of disease-associated regulatory variants in vivo using a versatile dual colour transgenesis strategy in zebrafish.

Disruption of gene regulation by sequence variation in non-coding regions of the genome is now recognised as a significant cause of human disease and disease susceptibility. Sequence variants in cis-regulatory elements (CREs), the primary determinants of spatio-temporal gene regulation, can alter transcription factor binding sites. While technological advances have led to easy identification of disease-associated CRE variants, robust methods for discerning functional CRE variants from background variation are lacking. Here we describe an efficient dual-colour reporter transgenesis approach in zebrafish, simultaneously allowing detailed in vivo comparison of spatio-temporal differences in regulatory activity between putative CRE variants and assessment of altered transcription factor binding potential of the variant. We validate the method on known disease-associated elements regulating SHH, PAX6 and IRF6 and subsequently characterise novel, ultra-long-range SOX9 enhancers implicated in the craniofacial abnormality Pierre Robin Sequence. The method provides a highly cost-effective, fast and robust approach for simultaneously unravelling in a single assay whether, where and when in embryonic development a disease-associated CRE-variant is affecting its regulatory function.

Phenotype and genotype analysis of a French cohort of 119 patients with CHARGE syndrome.

CHARGE syndrome (CS) is a genetic disorder whose first description included Coloboma, Heart disease, Atresia of choanae, Retarded growth and development, Genital hypoplasia, and Ear anomalies and deafness, most often caused by a genetic mutation in the CHD7 gene. Two features were then added: semicircular canal anomalies and arhinencephaly/olfactory bulb agenesis, with classification of typical, partial, or atypical forms on the basis of major and minor clinical criteria. The detection rate of a pathogenic variant in the CHD7 gene varies from 67% to 90%. To try to have an overview of this heterogenous clinical condition and specify a genotype-phenotype relation, we conducted a national study of phenotype and genotype in 119 patients with CS. Selected clinical diagnostic criteria were from Verloes (2005), updated by Blake & Prasad (). Besides obtaining a detailed clinical description, when possible, patients underwent a full ophthalmologic examination, audiometry, temporal bone CT scan, gonadotropin analysis, and olfactory-bulb MRI. All patients underwent CHD7 sequencing and MLPA analysis. We found a pathogenic CHD7 variant in 83% of typical CS cases and 58% of atypical cases. Pathogenic variants in the CHD7 gene were classified by the expected impact on the protein. In all, 90% of patients had a typical form of CS and 10% an atypical form. The most frequent features were deafness/semicircular canal hypoplasia (94%), pituitary defect/hypogonadism (89%), external ear anomalies (87%), square-shaped face (81%), and arhinencephaly/anosmia (80%). Coloboma (73%), heart defects (65%), and choanal atresia (43%) were less frequent.

Association between Zika virus and microcephaly in French Polynesia, 2013-15: a retrospective study.

BACKGROUND: The emergence of Zika virus in the Americas has coincided with increased reports of babies born with microcephaly. On Feb 1, 2016, WHO declared the suspected link between Zika virus and microcephaly to be a Public Health Emergency of International Concern. This association, however, has not been precisely quantified. METHODS: We retrospectively analysed data from a Zika virus outbreak in French Polynesia, which was the largest documented outbreak before that in the Americas. We used serological and surveillance data to estimate the probability of infection with Zika virus for each week of the epidemic and searched medical records to identify all cases of microcephaly from September, 2013, to July, 2015. Simple models were used to assess periods of risk in pregnancy when Zika virus might increase the risk of microcephaly and estimate the associated risk. FINDINGS: The Zika virus outbreak began in October, 2013, and ended in April, 2014, and 66% (95% CI 62-70) of the general population were infected. Of the eight microcephaly cases identified during the 23-month study period, seven (88%) occurred in the 4-month period March 1 to July 10, 2014. The timing of these cases was best explained by a period of risk in the first trimester of pregnancy. In this model, the baseline prevalence of microcephaly was two cases (95% CI 0-8) per 10,000 neonates, and the risk of microcephaly associated with Zika virus infection was 95 cases (34-191) per 10,000 women infected in the first trimester. We could not rule out an increased risk of microcephaly from infection in other trimesters, but models that excluded the first trimester were not supported by the data. INTERPRETATION: Our findings provide a quantitative estimate of the risk of microcephaly in fetuses and neonates whose mothers are infected with Zika virus. FUNDING: Labex-IBEID, NIH-MIDAS, AXA Research fund, EU-PREDEMICS.

Efficiency of prenatal diagnosis in Pierre Robin sequence.

OBJECTIVES: To analyze the efficiency of prenatal diagnosis of Pierre Robin sequence (PRS) regarding the final specific diagnosis and to determine whether infants have more severe respiratory disorders with than without prenatally suspected PRS. METHODS: Review of the outcome of all prenatal cases of suspected PRS managed in our prenatal diagnosis center during the last 15 years; analysis of the consistency between prenatal and postnatal diagnoses in 2 groups of women with and without a family history of PRS; comparison of the grades of disease severity for infants with and without prenatally suspected PRS. RESULTS: Fifty-nine files were studied. Prenatal and postnatal consistencies of a specific diagnosis of PRS were 100% for women with a family history of PRS and with prenatally suspected nonisolated PRS. It was 78.6% for those with prenatally suspected isolated PRS. We describe 13 terminations of pregnancy. The 41 children living beyond 18 months seem to have more functionally severe phenotypes than the 227 children without prenatally suspected PRS. CONCLUSION: Prenatal diagnosis of isolated PRS is a challenge as other features can be missed. Use of prenatal chromosomal microarray can improve the accuracy of diagnosis. In all cases, adequate neonatal care should be offered.

Congenital cerebral malformations and dysfunction in fetuses and newborns following the 2013 to 2014 Zika virus epidemic in French Polynesia.

We detected an unusual increase in congenital cerebral malformations and dysfunction in fetuses and newborns in French Polynesia, following an epidemic of Zika virus (ZIKV), from October 2013 to March 2014. A retrospective review identified 19 cases, including eight with major brain lesions and severe microcephaly, six with severe cerebral lesions without microcephaly and five with brainstem dysfunction without visible malformations. Imaging revealed profound neurological lesions (septal and callosal disruption, ventriculomegaly, abnormal neuronal migration, cerebellar hypoplasia, occipital pseudocysts, brain calcifications). Amniotic fluid was drawn from seven cases at gestation weeks 20 to 29. ZIKV RNA was detected by RT-PCR and infectious ZIKV isolates were obtained in four of five microcephalic, but not in two non-microcephalic cases with severe brain lesions. Medical termination of pregnancy was performed in eleven cases; two cases with brainstem dysfunction died in the first months of life; six cases are alive, with severe neurological impairment. The results show that four of seven tested fetuses with major neurological injuries were infected with ZIKV in utero. For other non-microcephalic, congenital abnormalities we were not able to prove or exclude ZIKV infection retrospectively. The unusual occurrence of brain malformations or dysfunction without microcephaly following a ZIKV outbreak needs further studies.

[Psychomotor education and speech therapy when weaning a child off artificial feeding]. / Psychomotricité et orthophonie lors du sevrage d'une nutrition artificielle chez l'enfant.

To support children and their families with weaning off artificial nutrition, a psychomotor therapist and speech therapist from the 'Pierre Robin syndrome and congenital sucking-swallowing disorders' specialist rare disease centre at Necker-Enfant Malades hospital in Paris, have set up a joint consultation, as a complement to medical consultations. This programme shows how speech therapy and psychomotor education can complement each other in order to help children and their parents during this difficult period.

Prenatal diagnosis of Pierre Robin Sequence: accuracy and ability to predict phenotype and functional severity.

OBJECTIVE: To assess the outcome of fetuses who had sonographic features suggestive of Pierre Robin Sequence (PRS). METHOD: All prenatal ultrasounds that mentioned 'posterior cleft palate', or 'micro or retrognathia' or 'PRS' over 13 and 20 years, respectively, at two obstetrical centers were reviewed. Medical records for children with isolated PRS monitored over 20 years at a PRS referral center for prenatal anomalies and the severity of neonatal feeding and respiratory functional disorders were utilized for comparison. RESULTS: From a prenatal ultrasound database of 166 000 cases, 157 had one or more of the sonographic signs suggestive of PRS and had follow-up available. Of them, 33 (21%) had confirmed PRS, 9 (6%) were normal and 115 (73%) had chromosomal aberrations, associated malformations or neurological anomalies. Visualization of a posterior cleft palate in addition to retro-micrognathia had a positive predictive value of 100% for PRS. The distribution of functional severity grades was similar in cases suspected prenatally as in 238 cases of PRS followed in the referral center in Necker Hospital. CONCLUSION: Only a minority of cases of fetal retrognathia have complete PRS; the majority have other severe conditions. Prenatal prediction of functional severity of isolated PRS is not possible.

Identification of novel craniofacial regulatory domains located far upstream of SOX9 and disrupted in Pierre Robin sequence.

Mutations in the coding sequence of SOX9 cause campomelic dysplasia (CD), a disorder of skeletal development associated with 46,XY disorders of sex development (DSDs). Translocations, deletions, and duplications within a ∼2 Mb region upstream of SOX9 can recapitulate the CD-DSD phenotype fully or partially, suggesting the existence of an unusually large cis-regulatory control region. Pierre Robin sequence (PRS) is a craniofacial disorder that is frequently an endophenotype of CD and a locus for isolated PRS at ∼1.2-1.5 Mb upstream of SOX9 has been previously reported. The craniofacial regulatory potential within this locus, and within the greater genomic domain surrounding SOX9, remains poorly defined. We report two novel deletions upstream of SOX9 in families with PRS, allowing refinement of the regions harboring candidate craniofacial regulatory elements. In parallel, ChIP-Seq for p300 binding sites in mouse craniofacial tissue led to the identification of several novel craniofacial enhancers at the SOX9 locus, which were validated in transgenic reporter mice and zebrafish. Notably, some of the functionally validated elements fall within the PRS deletions. These studies suggest that multiple noncoding elements contribute to the craniofacial regulation of SOX9 expression, and that their disruption results in PRS.

Heterogeneity of mutational mechanisms and modes of inheritance in auriculocondylar syndrome.

BACKGROUND: Auriculocondylar syndrome (ACS) is a rare craniofacial disorder consisting of micrognathia, mandibular condyle hypoplasia and a specific malformation of the ear at the junction between the lobe and helix. Missense heterozygous mutations in the phospholipase C, ß 4 (PLCB4) and guanine nucleotide binding protein (G protein), α inhibiting activity polypeptide 3 (GNAI3) genes have recently been identified in ACS patients by exome sequencing. These genes are predicted to function within the G protein-coupled endothelin receptor pathway during craniofacial development. RESULTS: We report eight additional cases ascribed to PLCB4 or GNAI3 gene lesions, comprising six heterozygous PLCB4 missense mutations, one heterozygous GNAI3 missense mutation and one homozygous PLCB4 intragenic deletion. Certain residues represent mutational hotspots; of the total of 11 ACS PLCB4 missense mutations now described, five disrupt Arg621 and two disrupt Asp360. The narrow distribution of mutations within protein space suggests that the mutations may result in dominantly interfering proteins, rather than haploinsufficiency. The consanguineous parents of the patient with a homozygous PLCB4 deletion each harboured the heterozygous deletion, but did not present the ACS phenotype, further suggesting that ACS is not caused by PLCB4 haploinsufficiency. In addition to ACS, the patient harbouring a homozygous deletion presented with central apnoea, a phenotype that has not been previously reported in ACS patients. CONCLUSIONS: These findings indicate that ACS is not only genetically heterogeneous but also an autosomal dominant or recessive condition according to the nature of the PLCB4 gene lesion.

Congenital heart defects in patients with deletions upstream of SOX9.

Heterozygous loss-of-function coding-sequence mutations of the transcription factor SOX9 cause campomelic dysplasia, a rare skeletal dysplasia with congenital bowing of long bones (campomelia), hypoplastic scapulae, a missing pair of ribs, pelvic, and vertebral malformations, clubbed feet, Pierre Robin sequence (PRS), facial dysmorphia, and disorders of sex development. We report here two unrelated families that include patients with isolated PRS, isolated congenital heart defect (CHD), or both anomalies. Patients from both families carried a very similar ∼1 Mb deletion upstream of SOX9. Analysis of ChIP-Seq from mouse cardiac tissue for H3K27ac, a marker of active regulatory elements, led us to identify several putative cardiac enhancers within the deleted region. One of these elements is known to interact with Nkx2.5 and Gata4, two transcription factors responsible for CHDs. Altogether, these data suggest that disruption of cardiac enhancers located upstream of SOX9 may be responsible for CHDs in humans.

Developmental outcome in Pierre Robin sequence: a longitudinal and prospective study of a consecutive series of severe phenotypes.

Pierre Robin sequence (PRS) is a congenital condition with a heterogeneous and imprecise developmental prognosis. We conducted a longitudinal prospective study analyzing the long-term developmental outcome of a consecutive series of 39 children with PRS who had an a priori good prognosis (isolated PRS or PRS associated with a Stickler syndrome) but severe neonatal disorders (respiratory and feeding difficulties). Psychomotor and cognitive levels, speech, and eating behavior were assessed at 15 months of age and 3 and 6 years of age; 24 of the oldest children were interviewed at age 11 or 12 years. Results were analyzed by diagnosis, extent of respiratory and feeding disorders, and treatment modalities. Cognitive scores were within normal ranges and increased over time, from 90.5 at 15 months of age to 109.1 at 6 years. The 24 oldest children were enrolled in the appropriate junior high school grade at the normal age. For children 15 months of age, language scores were below the average, as were scores for vocabulary at 3 years for half of the patients. At 6 years, children's speech showed persistent rhinolalia, which was mild (47%), moderate (11%), or major (11%). At 15 months of age, 74% of the children had satisfactory eating behavior, and 15% had serious difficulties. At 3 and 6 years, 18% and 6% of the children, respectively, had eating problems. Treatment modalities had no significant effect on long-term outcome. Global developmental quotient scores were lower but not significantly for children with an associated Stickler syndrome than those with isolated PRS. Children with isolated PRS showed good prognosis.

Limits of patient isolation measures to control extended-spectrum beta-lactamase-producing Enterobacteriaceae: model-based analysis of clinical data in a pediatric ward.

BACKGROUND: Extended-spectrum beta-lactamase-producing Enterobacteriaceae (ESBL-E) are a growing concern in hospitals and the community. How to control the nosocomial ESBL-E transmission is a matter of debate. Contact isolation of patients has been recommended but evidence supporting it in non-outbreak settings has been inconclusive. METHODS: We used stochastic transmission models to analyze retrospective observational data from a two-phase intervention in a pediatric ward, successively implementing single-room isolation and patient cohorting in an isolation ward, combined with active ESBL-E screening. RESULTS: For both periods, model estimates suggested reduced transmission from isolated/cohorted patients. However, most of the incidence originated from sporadic sources (i.e. independent of cross-transmission), unaffected by the isolation measures. When sporadic sources are high, our model predicted that even substantial efforts to prevent transmission from carriers would have limited impact on ESBL-E rates. CONCLUSIONS: Our results provide evidence that, considering the importance of sporadic acquisition, e.g. endogenous selection of resistant strains following antibiotic treatment, contact-isolation measures alone might not suffice to control ESBL-E. They also support the view that estimating cross-transmission extent is key to predicting the relative success of contact-isolation measures. Mathematical models could prove useful for those estimations and guide decisions concerning the most effective control strategy.

Study protocol for a multicenter, multinational, observational registry of epidemiology, treatment and outcome of patients with Robin sequence.

BACKGROUND: Robin sequence (RS) is a congenital condition characterized by micrognathia, glossoptosis and upper airway obstruction. Diagnosis and treatment are characterized by heterogeneity, resulting in a lack of uniformly collected data. METHODS: We have set up a prospective, observational, multicenter, multinational registry aimed at obtaining routine clinical data from RS patients receiving different treatment approaches and enabling an assessment of outcomes obtained through different therapeutic approaches. Patient enrolment has started in January 2022. Disease characteristics, adverse events and complications depending on the different diagnostic and treatment approaches and their effects on neurocognition, growth, speech development and hearing outcome are evaluated using routine clinical data. In addition to characterizing the patient population and comparing outcomes achieved with different treatment approaches, the registry will evolve to focus on endpoints such as quality of life and long-term developmental status. DISCUSSION: This registry will provide data on different treatment approaches collected during routine care with diverse framework conditions and will allow assessing diagnostic and therapeutic outcomes of children with RS. These data, urgently demanded by the scientific community, may contribute to refining and personalizing existing therapeutic approaches and increase knowledge about the long-term outcome of children born with this rare condition. TRIAL REGISTRATION: DRKS00025365.

Mild MDPL in a patient with a novel de novo missense variant in the Cys-B region of POLD1.

DNA polymerase δ is one of the three main enzymes responsible for DNA replication. POLD1 heterozygous missense variants in the exonuclease domain result in a cancer predisposition phenotype. In contrast, heterozygous variants in POLD1 polymerase domain have more recently been shown to be the underlying basis of the distinct autosomal dominant multisystem lipodystrophy disorder, MDPL (mandibular hypoplasia, deafness, progeroid features, and lipodystrophy syndrome OMIM # 615381), most commonly a recurrent in-frame deletion of serine at position 604, accounting for 18 of the 21 reported cases of this condition. One patient with an unusually severe phenotype has been reported, caused by a de novo c. 3209 T > A, (p.(Ile1070Asn)) variant in the highly conserved CysB motif in the C-terminal of the POLD1 protein. This region has recently been shown to bind an iron-sulphur cluster of the 4Fe-4S type. This report concerns a novel de novo missense variant in the CysB region, c.3219 G > C, (p.(Ser1073Arg)) in a male child with a milder phenotype. Using in silico analysis in the context of the recently published structure of human Polymerase δ holoenzyme, we compared these and other variants which lie in close proximity but result in differing degrees of severity and varying features. We hypothesise that the c.3219 G > C, (p.(Ser1073Arg)) substitution likely causes reduced binding of the iron-sulphur cluster without significant disruption of protein structure, while the previously reported c.3209 T > A (p.(Ile1070Asn)) variant likely has a more profound impact on structure and folding in the region. Our analysis supports a central role for the CysB region in regulating POLD1 activity in health and disease.