Phenotypic spectrum and genomics of undiagnosed arthrogryposis multiplex congenita

BACKGROUND

Arthrogryposis multiplex congenita (AMC) is characterised by congenital joint contractures in two or more body areas. AMC exhibits wide phenotypic and genetic heterogeneity. Our goals were to improve the genetic diagnosis rates of AMC, to evaluate the added value of whole exome sequencing (WES) compared with targeted exome sequencing (TES) and to identify new genes in 315 unrelated undiagnosed AMC families.

METHODS

Several genomic approaches were used including genetic mapping of disease loci in multiplex or consanguineous families, TES then WES. Sanger sequencing was performed to identify or validate variants.

RESULTS

We achieved disease gene identification in 52.7% of AMC index patients including nine recently identified genes (CNTNAP1, MAGEL2, ADGRG6, ADCY6, GLDN, LGI4, LMOD3, UNC50 and SCN1A). Moreover, we identified pathogenic variants in ASXL3 and STAC3 expanding the phenotypes associated with these genes. The most frequent cause of AMC was a primary involvement of skeletal muscle (40%) followed by brain (22%). The most frequent mode of inheritance is autosomal recessive (66.3% of patients). In sporadic patients born to non-consanguineous parents (n=60), de novo dominant autosomal or X linked variants were observed in 30 of them (50%).

CONCLUSION

New genes recently identified in AMC represent 21% of causing genes in our cohort. A high proportion of de novo variants were observed indicating that this mechanism plays a prominent part in this developmental disease. Our data showed the added value of WES when compared with TES due to the larger clinical spectrum of some disease genes than initially described and the identification of novel genes.

Frequency of differential placental transfer to twins of maternal antiretroviral medications

BACKGROUND

Placental passage of drugs in twins is poorly understood, and is unknown regarding antiretrovirals (ARVs). In the event of large differences in the exposure of 2 twins to the same maternal therapy, this could have a clinical impact in terms of prevention of perinatal HIV transmission or adverse effects.

OBJECTIVE

To describe the frequency of differential transplacental passage of antiretrovirals between twins.

STUDY DESIGN

The study was performed retrospectively, on data from women included in a multicenter perinatal HIV cohort study. All twin pairs for which the mother received antiretroviral therapy and for which drug concentrations in both of the umbilical cords after cord clamping at delivery were studied. We considered that a difference in concentrations of more than 50 % between twins was a substantial difference (ratios below 0.67 or above 1.50).

RESULTS

We analyzed 29 twin pairs, 27 dichorionic and 2 monochorionic diamniotic. Cord blood concentrations differed between the 2 twins by more than 50 % for at least one ARV in 9 twin pairs, 8 dichorionic and 1 monochorionic. Discordant concentrations were observed in one or more cases for several nucleoside reverse transcriptase inhibitors (tenofovir, emtricitabine, lamivudine, zidovudine) and protease inhibitors (atazanavir, lopinavir, saquinavir et ritonavir); within individual twin pairs placental transfer was discordant for one or more ARVs, but identical for others.

CONCLUSION

Concentrations differed in nearly one third of twin pairs. This may be due to interindividual genetic variability of placental transporters between dizygotic twins as well as physiological differences between twins.

Retrospective Description of Pregnant Women Infected with Severe Acute Respiratory Syndrome Coronavirus 2, France

Fix data are available on the management of pregnant women infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We conducted a retrospective study of 100 pregnant women with SARS-CoV-2 infection in 4 obstetric units in the Paris metropolitan area of France during March 12-April 13, 2020. Among patients, 52 (52%) were hospitalized, 10 (10%) in intensive care units (ICUs). Women with higher body mass indexes (BMIs; median 30.7 kg/m2) were more likely to be hospitalized in ICUs than other women (median BMI 26.2 kg/m2). Women hospitalized in ICUs had lower lymphocyte count at diagnosis (median 0.77 × 109 cells/L) than women not hospitalized in ICUs (median lymphocyte count 1.15 × 109 cells/L). All women requiring oxygen >5 L/min were intubated. Clinical and laboratory evaluation of SARS-CoV-2-positive pregnant women at the time of diagnosis can identify patients at risk for ICU hospitalization.

Neonatal morbidity associated with vaginal delivery of noncephalic second twins

BACKGROUND

Management of noncephalic second twin delivery rests on the results of population-based retrospective studies of twin births that have shown higher neonatal mortality and morbidity for second twins with noncephalic, compared with cephalic, presentations after vaginal delivery of the first twin. Because these studies are flawed by data of questionable validity, do not report the obstetrical practices at delivery, and do not allow collection of potential confounding variables, we performed a national prospective study specially designed to evaluate the management of twins' delivery.

OBJECTIVE

We sought to assess neonatal mortality and morbidity according to second twin presentation after vaginal birth of the first twin.

STUDY DESIGN

The Jumeaux Mode d'Accouchement study was a nationwide prospective population-based cohort study of twin deliveries performed in 176 maternity units in France from February 2014 through March 2015. The primary outcome was a composite of intrapartum mortality and neonatal mortality and morbidity. Neonatal outcomes of second twins born ≥32 weeks of gestation after vaginal delivery of the first cephalic or breech twin were compared according to the noncephalic or cephalic second twin presentation. Multivariable logistic regression models controlled for potential confounders. Subgroup analyses were conducted according to the breech or transverse presentation of the noncephalic second twin, and gestational age at delivery, before or after 37 weeks of gestation.

RESULTS

Among 3903 second twins enrolled in the study, 2384 (61.1%) were in cephalic and 1519 (38.9%) in noncephalic presentations, of whom 999 (25.6%) were in breech and 520 (13.3%) in transverse presentation. Composite neonatal mortality and morbidity did not differ between the noncephalic and cephalic group (47/1519 [3.1%] vs 59/2384 [2.5%]; adjusted odds ratio, 1.23; 95% confidence interval, 0.81-1.85). No significant difference between groups was shown for the primary outcome in subgroup analyses according to type of noncephalic second twin presentation or gestational age at delivery. Cesarean delivery rates for the second twin were lower in the breech than in the cephalic group (14/999 [1.4%] vs 75/2384 [3.1%], P = .003) and lower in the cephalic than in the transverse group (75/2384 [3.1%] vs 35/520 [6.7%], P < .001).

CONCLUSION

Noncephalic and cephalic second twin presentations after vaginal delivery of the first twin ≥32 weeks of gestation are associated with similar low composite neonatal mortality and morbidity. Vaginal delivery of noncephalic second twin is a reasonable option.

Severe X-linked chondrodysplasia punctata in nine new female fetuses

OBJECTIVES

Conradi-Hünermann-Happle [X-linked dominant chondrodysplasia punctata 2 (CDPX2)] syndrome is a rare X-linked dominant skeletal dysplasia usually lethal in men while affected women show wide clinical heterogeneity. Different EBP mutations have been reported. Severe female cases have rarely been reported, with only six antenatal presentations.

METHODS

To better characterize the phenotype in female fetuses, we included nine antenatally diagnosed cases of women with EBP mutations. All cases were de novo except for two fetuses with an affected mother and one case of germinal mosaicism.

RESULTS

The mean age at diagnosis was 22 weeks of gestation. The ultrasound features mainly included bone abnormalities: shortening (8/9 cases) and bowing of the long bones (5/9), punctuate epiphysis (7/9) and an irregular aspect of the spine (5/9). Postnatal X-rays and examination showed ichthyosis (8/9) and epiphyseal stippling (9/9), with frequent asymmetric short and bowed long bones. The X-inactivation pattern of the familial case revealed skewed X-inactivation in the mildly symptomatic mother and random X-inactivation in the severe fetal case. Differently affected skin samples of the same fetus revealed different patterns of X-inactivation.

CONCLUSION

Prenatal detection of asymmetric shortening and bowing of the long bones and cartilage stippling should raise the possibility of CPDX2 in female fetuses, especially because the majority of such cases involve de novo mutations.

Mutations in CNTNAP1 and ADCY6 are responsible for severe arthrogryposis multiplex congenita with axoglial defects

Non-syndromic arthrogryposis multiplex congenita (AMC) is characterized by multiple congenital contractures resulting from reduced fetal mobility. Genetic mapping and whole exome sequencing (WES) were performed in 31 multiplex and/or consanguineous undiagnosed AMC families. Although this approach identified known AMC genes, we here report pathogenic mutations in two new genes. Homozygous frameshift mutations in CNTNAP1 were found in four unrelated families. Patients showed a marked reduction in motor nerve conduction velocity (<10 m/s) and transmission electron microscopy (TEM) of sciatic nerve in the index cases revealed severe abnormalities of both nodes of Ranvier width and myelinated axons. CNTNAP1 encodes CASPR, an essential component of node of Ranvier domains which underlies saltatory conduction of action potentials along the myelinated axons, an important process for neuronal function. A homozygous missense mutation in adenylate cyclase 6 gene (ADCY6) was found in another family characterized by a lack of myelin in the peripheral nervous system (PNS) as determined by TEM. Morpholino knockdown of the zebrafish orthologs led to severe and specific defects in peripheral myelin in spite of the presence of Schwann cells. ADCY6 encodes a protein that belongs to the adenylate cyclase family responsible for the synthesis of cAMP. Elevation of cAMP can mimic axonal contact in vitro and upregulates myelinating signals. Our data indicate an essential and so far unknown role of ADCY6 in PNS myelination likely through the cAMP pathway. Mutations of genes encoding proteins of Ranvier domains or involved in myelination of Schwann cells are responsible for novel and severe human axoglial diseases.