Pathological and sonographic review of early isolated severe lower urinary tract obstruction and implications for prenatal treatment.

OBJECTIVE: To identify favorable renal histology in fetuses with early severe lower urinary tract obstruction (LUTO) and determine the best timing and selection criteria for prenatal surgery. METHODS: This multicenter, retrospective study included male fetuses with severe LUTO which died before 24 weeks of gestation during the period January 2000 to December 2018. Age-matched controls were used as reference standard for renal histology. Prenatal ultrasound features and fetal serum and/or urine ß2microglobulin level were retrieved and kidney histology slides (hematein-eosin-safran and α-smooth-muscle-actin (αSMA) immunostaining) were prepared and reviewed. αSMA-positive staining of the blastema is due to its aberrant differentiation into myofibroblastic cells. Cases were sorted into histopathologic groups (favorable or unfavorable) according to the blastema's morphology and αSMA labeling and the data of these groups were compared. RESULTS: Included in the study were 74 fetuses with a median gestational age at outcome of 17 + 6 (range, 13 + 0 to 23 + 5) weeks. Parenchymal organization was preserved in 48% of the kidneys. A blastema was present in 90% of the kidneys, but it was morphologically normal in only 9% and αSMA-negative in only 1% of them. Most (82%) fetuses had an unfavorable prognosis, and 36% of fetuses died ≤ 18 weeks and had severe renal lesions detected on histology (early unfavorable prognosis). A favorable renal prognosis was associated with an earlier gestational age (P = 0.001). Fetuses with LUTO had a significantly lower number of mature glomeruli (P < 0.001) compared with controls. However, there was no significant difference in the number of glomeruli generations between the early-unfavorable-prognosis group (≤ 18 weeks) and the group with a favorable prognosis (P = 0.19). A comparison of prenatal ultrasound features and biochemical markers between groups could not identify any prenatal selection criteria. CONCLUSIONS: Before 18 weeks, around 30% of fetuses with severe LUTO still have potential for kidney development. Identification of these cases would enable them to be targeted for prenatal therapy. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Heterogeneity in defining fetal corpus callosal pathology: systematic review.

OBJECTIVE: Fetal anomalies of the corpus callosum (CC) have been reported in the prenatal imaging literature since 1985, and, especially when isolated, pose challenges for both the patient and fetal medicine specialist. The purpose of this study was to review systematically the literature on prenatally diagnosed abnormalities of the CC, focusing on the terminology used to describe abnormalities other than complete agenesis of the CC, and to assess the heterogeneity of the nomenclature and definitions used. METHODS: This study was conducted in accordance with the PRISMA statement for reporting systematic reviews. A literature search was performed to identify prospective or retrospective case series or cohort studies, published in English, French, Italian, German or Spanish, reporting fetal imaging findings and describing anomalies of the CC. Quality and risk of bias of the studies were evaluated using the Newcastle-Ottawa scale and a modification of the scale developed by Conde-Agudelo et al. for other fetal imaging studies. The data extracted included the number of patients, the number of different anomalies identified, the descriptive names of the anomalies, and, where applicable, the definitions of the anomalies, the number of cases of each type of anomaly and the biometric charts used. Secondary tests used to confirm the diagnosis, as well as the postnatal or post-termination tests used to ascertain the diagnosis, were also recorded. RESULTS: The search identified 998 records, and, after review of titles and abstracts and full review of 45 papers, 27 studies were included initially in the review, of which 24 were included in the final analysis. These 24 studies had a broad range of quality and risk of bias and represented 1135 cases of CC anomalies, of which 49% were complete agenesis and the remainder were described using the term partial agenesis or nine other terms, of which five had more than one definition. CONCLUSIONS: In comparison to the postnatal literature, in the prenatal literature there is much greater heterogeneity in the nomenclature and definition of CC anomalies other than complete agenesis. This heterogeneity and lack of standard definitions in the prenatal literature make it difficult to develop large multicenter pooled cohorts of patients who can be followed in order to develop a better understanding of the genetic associations and neurodevelopmental and psychological outcomes of patients with CC anomalies. As this information is important to improve counseling of these patients, a good first step towards this goal would be to develop a simpler categorization of prenatal CC anomalies that matches better the postnatal literature. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Re-focusing on Agnathia-Otocephaly complex.

OBJECTIVES: Agnathia-otocephaly complex is a rare condition characterized by mandibular hypoplasia or agnathia, ear anomalies (melotia/synotia) and microstomia with aglossia. This severe anomaly of the first branchial arch is most often lethal. The estimated incidence is less than 1 in 70.000 births, with etiologies linked to both genetic and teratogenic factors. Most of the cases are sporadic. To date, two genes have been described in humans to be involved in this condition: OTX2 and PRRX1. Nevertheless, the overall proportion of mutated cases is unknown and a significant number of patients remain without molecular diagnosis. Thus, the involvement of other genes than OTX2 and PRRX1 in the agnathia-otocephaly complex is not unlikely. Heterozygous mutations in Cnbp in mice are responsible for mandibular and eye defects mimicking the agnathia-otocephaly complex in humans and appear as a good candidate. Therefore, in this study, we aimed (i) to collect patients presenting with agnathia-otocephaly complex for screening CNBP, in parallel with OTX2 and PRRX1, to check its possible implication in the human phenotype and (ii) to compare our results with the literature data to estimate the proportion of mutated cases after genetic testing. MATERIALS AND METHODS: In this work, we describe 10 patients suffering from the agnathia-otocephaly complex. All of them benefited from array-CGH and Sanger sequencing of OTX2, PRRX1 and CNBP. A complete review of the literature was made using the Pubmed database to collect all the patients described with a phenotype of agnathia-otocephaly complex during the 20 last years (1998-2019) in order (i) to study etiology (genetic causes, iatrogenic causes…) and (ii), when genetic testing was performed, to study which genes were tested and by which type of technologies. RESULTS: In our 10 patients' cohort, no point mutation in the three tested genes was detected by Sanger sequencing, while array-CGH has allowed identifying a 107-kb deletion encompassing OTX2 responsible for the agnathia-otocephaly complex phenotype in 1 of them. In 4 of the 70 cases described in the literature, a toxic cause was identified and 22 out the 66 remaining cases benefited from genetic testing. Among those 22 patients, 6 were carrying mutation or deletion in the OTX2 gene and 4 in the PRRX1 gene. Thus, when compiling results from our cohort and the literature, a total of 32 patients benefited from genetic testing, with only 34% (11/32) of patients having a mutation in one of the two known genes, OTX2 or PRRX1. CONCLUSIONS: From our work and the literature review, only mutations in OTX2 and PRRX1 have been found to date in patients, explaining around one third of the etiologies after genetic testing. Thus, agnathia-otocephaly complex remains unexplained in the majority of the patients, which indicates that other factors might be involved. Although involved in first branchial arch defects, no mutation in the CNBP gene was found in this study. This suggests that mutations in CNBP might not be involved in such phenotype in humans or that, unlike in mice, a compensatory effect might exist in humans. Nevertheless, given that agnathia-otocephaly complex is a rare phenotype, more patients have to be screened for CNBP mutations before we definitively conclude about its potential implication. Therefore, this work presents the current state of knowledge on agnathia-otocephaly complex and underlines the need to expand further the understanding of the genetic bases of this disorder, which remains largely unknown. CLINICAL RELEVANCE: We made here an update and focus on the clinical and genetic aspects of agnathia-otocephaly complex as well as a more general review of craniofacial development.

Autosomal recessive IFT57 hypomorphic mutation cause ciliary transport defect in unclassified oral-facial-digital syndrome with short stature and brachymesophalangia.

The 13 subtypes of oral-facial-digital syndrome (OFDS) belong to the heterogeneous group of ciliopathies. Disease-causing genes encode for centrosomal proteins, components of the transition zone or proteins implicated in ciliary signaling. A unique consanguineous family presenting with an unclassified OFDS with skeletal dysplasia and brachymesophalangia was explored. Homozygosity mapping and exome sequencing led to the identification of a homozygous mutation in IFT57, which encodes a protein implicated in ciliary transport. The mutation caused splicing anomalies with reduced expression of the wild-type transcript and protein. Both anterograde ciliary transport and sonic hedgehog signaling were significantly decreased in subjects' fibroblasts compared with controls. Sanger sequencing of IFT57 in 13 OFDS subjects and 12 subjects with Ellis-Van Creveld syndrome was negative. This report identifies the implication of IFT57 in human pathology and highlights the first description of a ciliary transport defect in OFDS, extending the genetic heterogeneity of this subgroup of ciliopathies.

MOLAR TOOTH SIGN AND ACROCALLOSAL SYNDROME--A REPORT ON A POLISH FAMILY AND REVIEW OF KIF7 SYNDROMOLOGY.

Acrocallosal syndrome is a multiple congenital anomaly disorder characterized by postaxial and/or preaxial polydactyly, cutaneous syndactyly, macrocephaly, widely spaced eyes, absence or hypoplasia of the corpus callosum, and intellectual disability. It was first described by Albert Schinzel as early as in 1979, but the diagnosis of this syndrome still remains challenging. Here we report a family with 2 sibs with acrocallosal syndrome caused by novel mutations in KIF7. They present with features like molar tooth sign and hyperventilation that are not very typical in ACLS, but do occur in other ciliopathies, hence we also discuss the clinical heterogeneity of KIF7-associated disorders.

Posterior fossa imaging in 158 children with ataxia.

OBJECTIFS: To propose a MRI cerebellar algorithm that may be applied to guide genetic/malformative or biochemical investigations for patients with cerebellar ataxia. PATIENTS AND METHODS: Cerebral MRI of 158 patients with cerebellar ataxia and no supratentorial abnormality were examined according to a new categorization system based on posterior fossa imaging. The clinical and radiological findings were confronted to biochemical and/or genetic results using the MR cerebellar algorithm. Seven groups of cerebellar MRI pattern were described: vermian dysgenesis (n=27), cerebellar hypoplasia (n=15), hemispheric cerebellar dysgenesis (n=6), unilateral hemispheric atrophy (n=5), global cerebellar atrophy (n=84), signal abnormalities (n=11) and normal MRI (n=10). Cerebellar hypoplasia, vermian dysgenesis and hemispheric cerebellar dysgenesis groups were classified as malformative disorders. Global atrophy and signal abnormality groups were classified as metabolic disorders. RESULTS: In the vermian dysgenesis group, a specific genetic diagnosis was obtained in eight children (8/27) and all of the mutated genes (AHI1 (JBS3), CEP290 (JBS5), TMEM67 (JBS6), and RPGRIP1L (JBS7)) are involved in primary cilia function. In the group of pontocerebellar hypoplasia specific genetic diagnosis was obtained in one patient (PCH2) (1/15). Thus, nine of 42 children classified as malformative disorder had a molecular diagnosis. Global atrophy and signal abnormality groups were classified as metabolic disorders, specific biochemical was obtained in 46/95 children. In global atrophy group, respiratory chain deficiency was diagnosed in 18 children (18/84). In 21 children a congenital disorders of glycosylation type 1a (CDG Ia) was diagnosed (21/84) and infantile neuroaxonale dystrophy (INAD) was diagnosed in one child. In signal abnormalities group, specific biochemical diagnosis was obtained in six out of 11 children, five children with respiratory chain deficiency and one child with sulphite oxidase deficiency. In hemispheric cerebellar dysgenesis and normal MRI groups, no biological diagnosis was found for any of the patients. In the group of unilateral hemispheric atrophy, we hypothesized a clastic prenatal injury. CONCLUSION: The proposed MR cerebellar algorithm was useful to guide genetic/malformative or biochemical investigations, allowing an etiological diagnosis in 55 children.

Genotype phenotype correlation of 30 patients with Smith-Magenis syndrome (SMS) using comparative genome hybridisation array: cleft palate in SMS is associated with larger deletions.

BACKGROUND: Smith-Magenis syndrome (SMS) is rare (prevalence 1 in 25 000) and is associated with psychomotor delay, a particular behavioural pattern and congenital anomalies. SMS is often due to a chromosomal deletion of <4 Mb at the 17p11.2 locus, leading to haploinsufficiency of numerous genes. Mutations of one of these gemes, RAI1, seems to be responsible for the main features found with heterozygous 17p11.2 deletions. METHODS: We studied DNA from 30 patients with SMS using a 300 bp amplimers comparative genome hybridisation array encompassing 75 loci from a 22 Mb section from the short arm of chromosome 17. RESULTS: Three patients had large deletions (10%). Genotype-phenotype correlation showed that two of them had cleft palate, which was not found in any of the other patients with SMS (p<0.007, Fisher's exact test). The smallest extra-deleted region associated with cleft palate in SMS is 1.4 Mb, contains <16 genes and is located at 17p11.2-17p12. Gene expression array data showed that the ubiquitin B precursor (UBB) is significantly expressed in the first branchial arch in the fourth and fifth weeks of human development. CONCLUSION: These data support UBB as a good candidate gene for isolated cleft palate.

Epistatic interactions with a common hypomorphic RET allele in syndromic Hirschsprung disease.

Hirschsprung disease (HSCR) stands as a model for genetic dissection of complex diseases. In this model, a major gene, RET, is involved in most if not all cases of isolated (i.e., nonsyndromic) HSCR, in conjunction with other autosomal susceptibility loci under a multiplicative model. HSCR susceptibility alleles can harbor either heterozygous coding sequence mutations or, more frequently, a polymorphism within intron 1, leading to a hypomorphic RET allele. On the other hand, about 30% of HSCR are syndromic. Hitherto, the disease causing gene has been identified for eight Mendelian syndromes with HSCR: congenital central hypoventilation (CCHS), Mowat-Wilson (MWS), Bardet-Biedl (BBS), Shah-Waardenburg (WS4), cartilage-hair-hypoplasia (CHH), Smith-Lemli-Opitz (SLO), Goldberg-Sprintzsen (GSS), and hydrocephalus due to congenital stenosis of the aqueduct of sylvius (HSAS). According to the HSCR syndrome, the penetrance of HSCR trait varies from 5 to 70%. Trisomy 21 (T21) also predisposes to HSCR. We were able to collect a series of 393 patients affected by CCHS (n = 173), WS4 (n = 24), BBS (n = 51), MWS (n = 71), T21 (n = 46), and mental retardation (MR) with HSCR (n = 28). For each syndrome, we studied the RET locus in two subgroups of patients; i.e., with or without HSCR. We genotyped the RET locus in 393 patients among whom 195 had HSCR, and compared the distribution of alleles and genotypes within the two groups for each syndrome. RET acts as a modifier gene for the HSCR phenotype in patients with CCHS, BBS, and Down syndrome, but not in patients with MWS and WS4. The frequent, low penetrant, predisposing allele of the RET gene can be regarded as a risk factor for the HSCR phenotype in CCHS, BBS, and Down syndrome, while its role is not significant in MWS and WS4. These data highlight the pivotal role of the RET gene in both isolated and syndromic HSCR.

High throughput SNP and expression analyses of candidate genes for non-syndromic oral clefts.

BACKGROUND: Recent work suggests that multiple genes and several environmental risk factors influence risk for non-syndromic oral clefts, one of the most common birth defects in humans. Advances in high-throughput genotyping technology now make it possible to test multiple markers in many candidate genes simultaneously. METHODS: We present findings from family based association tests of single nucleotide polymorphism (SNP) markers in 64 candidate genes genotyped using the BeadArray approach in 58 case-parent trios from Maryland (USA) to illustrate how multiple markers in multiple genes can be analysed. To assess whether these genes were expressed in human craniofacial structures relevant to palate and lip development, we also analysed data from the Craniofacial and Oral Gene Expression Network (COGENE) consortium, and searched public databases for expression profiles of these genes. RESULTS: Thirteen candidate genes showed significant evidence of linkage in the presence of disequilibrium, and ten of these were found to be expressed in relevant embryonic tissues: SP100, MLPH, HDAC4, LEF1, C6orf105, CD44, ALX4, ZNF202, CRHR1, and MAPT. Three other genes showing statistical evidence (ADH1C, SCN3B, and IMP5) were not expressed in the embryonic tissues examined here. CONCLUSIONS: This approach demonstrates how statistical evidence on large numbers of SNP markers typed in case-parent trios can be combined with expression data to identify candidate genes for complex disorders. Many of the genes reported here have not been previously studied as candidates for oral clefts and warrant further investigation.

Phenotypic spectrum of CHARGE syndrome in fetuses with CHD7 truncating mutations correlates with expression during human development.

BACKGROUND: The acronym CHARGE refers to a non-random cluster of malformations including coloboma, heart malformation, choanal atresia, retardation of growth and/or development, genital anomalies, and ear anomalies. This set of multiple congenital anomalies is frequent, despite rare patients with normal intelligence, and prognosis remains poor. Recently, CHD7 gene mutations have been identified in CHARGE patients; however, the function of CHD7 during development remains unknown. METHODS: We studied a series of 10 antenatal cases in whom the diagnosis of CHARGE syndrome was suspected, considering that a careful pathological description would shed light on the CHD7 function during development. CHD7 sequence analysis and in situ hybridisation were employed. RESULTS: The diagnosis of CHARGE syndrome was confirmed in all 10 fetuses by the identification of a CHD7 heterozygous truncating mutation. Interestingly, arhinencephaly and semi-circular canal agenesis were two constant features which are not included in formal diagnostic criteria so far. In situ hybridisation analysis of the CHD7 gene during early human development emphasised the role of CHD7 in the development of the central nervous system, internal ear, and neural crest of pharyngeal arches, and more generally showed a good correlation between specific CHD7 expression pattern and the developmental anomalies observed in CHARGE syndrome. CONCLUSIONS: These results allowed us to further refine the phenotypic spectrum of developmental anomalies resulting from CHD7 dysfunction.

L-carnitine is synthesized in the human fetal-placental unit: potential roles in placental and fetal metabolism.

Carnitine plays an indispensable role in fatty acid oxidation. Previous studies revealed that fetal carnitine is derived from the mother via transplacental transfer. Recent studies demonstrated the presence and importance of an active fatty acid oxidation system in the human placenta and in the human fetus. In view of these findings we decided to study carnitine metabolism in the fetal-placental unit by measuring carnitine metabolites, intermediary metabolites of carnitine biosynthesis, as well as the activity of carnitine biosynthesis enzymes in human term placenta, cord blood and selected embryonic and fetal tissues (5-20 weeks of development). Placenta contained low but detectable activity of gamma-butyrobetaine dioxygenase. This enzyme, which was considered to be expressed only in kidney, liver and brain, catalyzes the last step in the carnitine biosynthesis pathway. In addition, our results show that human fetal kidney, liver and spinal cord already have the capacity to synthesize carnitine. The ability of the placenta and fetus to synthesize carnitine suggests that in circumstances when maternal carnitine supply is limited, carnitine biosynthesis by the fetal-placental unit may supply sufficient carnitine for placental and fetal metabolism.

Expression and mutation analysis of BRUNOL3, a candidate gene for heart and thymus developmental defects associated with partial monosomy 10p.

Partial monosomy 10p is a rare chromosomal aberration. Patients often show symptoms of the DiGeorge/velocardiofacial syndrome spectrum. The phenotype is the result of haploinsufficiency of at least two regions on 10p, the HDR1 region associated with hypoparathyroidism, sensorineural deafness, and renal defects (HDR syndrome) and the more proximal region DGCR2 responsible for heart defects and thymus hypoplasia/aplasia. While GATA3 was identified as the disease causing gene for HDR syndrome, no genes have been identified thus far for the symptoms associated with DGCR2 haploinsufficiency. We constructed a deletion map of partial monosomy 10p patients and narrowed the critical region DGCR2 to about 300 kb. The genomic draft sequence of this region contains only one known gene, BRUNOL3 ( NAPOR, CUGBP2, ETR3). In situ hybridization of human embryos and fetuses revealed as well as in other tissues a strong expression of BRUNOL3 in thymus during different developmental stages. BRUNOL3 appears to be an important factor for thymus development and is therefore a candidate gene for the thymus hypoplasia/aplasia seen in partial monosomy 10p patients. We did not find BRUNOL3 mutations in 92 DiGeorge syndrome-like patients without chromosomal deletions and in 8 parents with congenital heart defect children.

PAX2 mutations in renal-coloboma syndrome: mutational hotspot and germline mosaicism.

The renal-coloboma syndrome (RCS, MIM 120330) is an autosomal dominant disorder caused by PAX2 gene mutations. We screened the entire coding sequence of the PAX2 gene for mutations in nine patients with RCS. We found five heterozygous PAX2 gene mutations: a dinucleotide insertion (2G) at position 619 in one sporadic RCS case, a single nucleotide insertion (619 + G) in three unrelated cases, and a single nucleotide deletion in a familial case. In this familial case, three affected sibs showed a striking ocular phenotypic variability. Each of the sibs carried a 619insG mutation, whilst unaffected parents did not, suggesting the presence of germline mosaicism. Interestingly, the 619insG mutation has been previously reported in several patients and is also responsible for the Pax21Neu mouse mutant, an animal model of human RCS. This study confirms the critical role of the PAX2 gene in human renal and ocular development. In addition, it emphasises the high variability of ocular defects associated with PAX2 mutations ranging from subtle optic disc anomalies to microphthalmia. Finally, the presence of PAX2 germline mosaicism highlights the difficulties associated with genetic counselling for PAX2 mutations.

Pathophysiology of syndromic combined pituitary hormone deficiency due to a LHX3 defect in light of LHX3 and LHX4 expression during early human development.

The pathophysiology of combined pituitary hormone deficiency (CPHD) is just beginning to be elucidated, with mutations in genes encoding transcription factors expressed at different stages of pituitary development. Among them, the two closely related genes, LHX3 and LHX4, are believed to share redundant biological properties. The patients with a LHX3 mutation display a CPHD phenotype, associated with a rigid cervical spine. This latter feature, not reported in Lhx3-/- and Lhx4-/- mice nor in patients with a LHX4 defect, prompted us to study the molecular consequences of a previously identified LHX3 23-bp deletion and to determine the LHX3 and LHX4 expression patterns during early human development. This deletion, which results in the skipping of one coding exon, would lead to a protein with no transcriptional capability. Using in situ hybridization, we show that LHX3 and LHX4 are expressed in the developing human pituitary and along the rostro-caudal length of the spinal cord; here, both transcripts are detected in the ventral part giving rise to motorneurons and interneurons. However, whereas LHX3 is expressed at all stages studied, LHX4 expression is transient, and, at 6 weeks of development, is stronger at the caudal than at the cervical level.

Expression of the RET proto-oncogene in human embryos.

The patterns of RET proto-oncogene expression in mouse, rat, and chicken and the anomalies observed in targeted RET mutants suggest that RET plays a major role in development of mouse enteric nervous system and in kidney organogenesis. Here, we report on in situ hybridization studies describing the pattern of RET proto-oncogene expression during early development of human embryos between 23 and 42 days. We show that the RET gene is expressed in the developing kidney (nephric duct, mesonephric tubules, and ureteric bud), the presumptive enteric neuroblasts of the developing enteric nervous system, cranial ganglia (VII+VIII, IX, and X) and in the presumptive motor neurons of the spinal cord. Yet, despite the high level of RET gene expression in the kidney and in the motor neurons of the developing central nervous system in human embryos, only rare cases with renal agenesis have been reported in Hirschsprung disease patients, and no clinical evidence of spinal cord involvement has been shown in patients carrying RET germline mutations (i.e., multiple endocrine neoplasia syndromes and Hirschsprung disease).

Expression of the PAX2 gene in human embryos and exclusion in the CHARGE syndrome.

The CHARGE syndrome comprises ocular coloboma, heart malformation, choanal atresia, retarded growth and development, central nervous system malformations, genital hypoplasia, ear abnormalities, or deafness. The cause of the CHARGE syndrome remains unknown. In the present study, we analyzed the distribution pattern of the PAX2 gene in human embryos and found that PAX2 gene expression occurs in the primordia affected in the CHARGE syndrome. These data prompted us to consider the PAX2 gene a candidate gene in the CHARGE "association." We analyzed the PAX2 gene in 34 patients fulfilling the diagnostic criteria of the CHARGE syndrome for deletion and nucleotidic variations of the coding sequence and identified only polymorphisms. Our data suggest that mutation of the PAX2 gene is not a cause of the CHARGE association. However, the pattern of expression of PAX2 suggests that genes encoding downstream targets effectors could be candidate genes for the CHARGE syndrome.

Monozygotic twins discordant for 18q21.2qter deletion detected by array CGH in amniotic fluid.

Discordant chromosomal anomalies in monozygotic twins may be caused by various timing issues of erroneous mitosis and twinning events. Here, we report a prenatal diagnosis of heterokaryotypic monozygotic twins discordant for phenotype. In a 28-year-old woman, ultrasound examination performed at 26 weeks of gestation, detected intrauterine growth restriction and unilateral cleft lip and palate in twin B, whereas twin A had normal fluid, growth and anatomy. Molecular karyotyping in twin B identified a 18q21.2qter deletion, further confirmed by FISH analysis on amniocytes. Interestingly, in twin A, cytogenetic studies (FISH analysis and karyotype) on amniocytes were normal. Genotyping with microsatellite markers confirmed the monozygosity of the twins. At 32 weeks of gestation, selective termination of twin B was performed by umbilical cord coagulation and fetal blood samples were taken from the umbilical cord in both twins. FISH analyses detected mosaicism in both twins with 75% of cells being normal and 25% harboring the 18qter deletion. After genetic counseling, the parents elected to terminate the second twin at 36 weeks of gestation. In postmortem studies, FISH analyses revealed mosaicism on several tissues in both twins. Taking into account this observation, we discuss the difficulties of genetic counseling and management concerning heterokaryotypic monozygotic twins.

[Prenatal symptoms and diagnosis of inherited metabolic diseases]. / Maladies héréditaires du métabolisme : signes anténatals et diagnostic biologique.

Inherited metabolic diseases are mostly due to enzyme deficiency in one of numerous metabolic pathways, leading to absence of a compound downstream from and the accumulation of a compound upstream from the deficient metabolite(s). Diseases of intoxication by proteins (aminoacidopathies, organic acidurias, urea cycle defects) and by sugars (galactosemia, fructosemia) usually do not give prenatal symptoms since mothers protect their fetuses from pathological metabolite accumulation. A well-known exception is hypoplasia of corpus callosum, as is sometimes observed in nonketotic hyperglycinemia and sulfite oxidase deficiency. Conversely, women with phenylketonuria "poison" their fetus if they are not treated (spontaneous abortions, intrauterine growth restriction [IUGR], cardiac malformations, and brain disease). Amino acid synthesis defects can lead to prenatal symptoms: microcephaly in serine deficiency (detectable by amino acid analysis in fetal cord blood), and brain malformations in glutamine synthetase deficiency. Impaired folate metabolism is involved in a large fraction of neurodevelopmental defects referred to as spina bifida, yet the underlying genetic component(s) are largely unknown. Energy metabolism diseases caused by defects in the synthesis or utilization of relevant metabolites lead to organ dysfunctions or malformations, but prenatal diagnosis is usually impossible unless genetic analysis can rely on a previously affected child in the family. A somewhat intermediate condition is defects of mitochondrial beta-oxidation of fatty acids, as they may sometimes be symptomatic prenatally (notably the HELLP syndrome or other presentations), and in this case, organic acid and acylcarnitine analysis in amniotic fluid can be informative in the absence of an index case. In contrast, complex molecule diseases commonly give prenatal symptoms that may permit the diagnosis even in the absence of index cases: hydrops fetalis and skeletal anomalies in lysosomal storage diseases, hydrops fetalis in congenital disorders of glycosylation (CDG) and transaldolase deficiency, brain malformations in O-glycosylation defects, brain malformations, kidney cysts and skeletal anomalies in peroxysomal diseases (Zellweger syndrome), syndactyly, genitalia malformations, and IUGR in Smith-Lemli-Opitz (SLO) syndrome. Although many metabolic disorders show biochemical abnormalities during fetal development that are informative for prenatal diagnosis, only a fraction of them are clinically/sonographically symptomatic before birth, thus allowing for prenatal diagnosis in the absence of an index case, i.e., serine deficiency, some fatty acid beta-oxidation defects, transaldolase deficiency, lysosomal diseases, CDG, Zellweger syndrome, and SLO syndrome.