Antenatal manifestations of inborn errors of metabolism: prenatal imaging findings

Clinical and molecular data in cases of prenatal localized overgrowth disorder: major implication of genetic variants in PI3K-AKT-mTOR signaling pathway

OBJECTIVES

To describe clinical and molecular findings in a French multicenter cohort of fetuses with prenatal diagnosis of congenital abnormality and suspicion of a localized overgrowth disorder (LOD) suggestive of genetic variants in the PI3K-AKT-mTOR signaling pathway.

METHODS

We analyzed retrospectively data obtained between 1 January 2013 and 1 May 2020 from fetuses with brain and/or limb overgrowth referred for molecular diagnosis of PI3K-AKT-mTOR pathway genes by next-generation sequencing (NGS) using pathological tissue obtained by fetal autopsy. We also assessed the diagnostic yield of amniotic fluid.

RESULTS

During the study period, 21 subjects with LOD suspected of being secondary to a genetic variant of the PI3K-AKT-mTOR pathway were referred for analysis. Of these, 17 fetuses had brain overgrowth, including six with isolated megalencephaly (MEG) and 11 with hemimegalencephaly (HMEG). Of the six with MEG, germline variants were identified in four cases, in either PIK3R2, AKT3 or MTOR, and a postzygotic PIK3R2 variant was found in the other two cases. Of the 11 with HMEG, a postzygotic PIK3CA variant was found in three fetuses with extracerebral features of PIK3CA-related overgrowth spectrum, and in seven fetuses with isolated HMEG. No pathogenic variant was identified in the 11^th case with HMEG. Four fetuses with limb overgrowth also had one or more lymphatic malformations (LM) and harbored a postzygotic PIK3CA variant. NGS on cultured amniocytes performed in 10 cases, of which nine had been found positive on analysis of pathological fetal tissue, showed variants in four, in either PIK3CA, PIK3R2 or AKT3.

CONCLUSIONS

Isolated MEG or HMEG may lead to identification of genetic variants in the PI3K-AKT-mTOR signaling pathway. Cases of limb overgrowth and LM or isolated HMEG are likely associated with PIK3CA variants. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

A 7-Year Report of Spectrum of Inborn Errors of Metabolism on Full-Term and Premature Infants in a Chinese Neonatal Intensive Care Unit

Inborn errors of metabolism (IEMs) have great repercussions in neonatal intensive care units (NICUs). However, the integrative analysis of the incidence for full-term and premature neonates of IEMs in NICUs have not been reported. In this study, we aimed to estimate the incidence of IEMs in the NICU population so as to better evaluate the impact of IEMs on Chinese NICUs. A total of 42,257 newborns (proportion of premature as 36.7%) enrolled to the largest Chinese NICU center for a sequential 7 years screen, and 66 were diagnosed with IEMs. The prevalence of IEMs in total, full-term, and premature infants was 1:640, 1:446, and 1:2,584, respectively. In spectrum of our NICU, diseases that cause endogenous intoxication like methylmalonic acidemia accounted for 93.9% (62/66), and this ratio was higher in full-term infants with 98.3% (59/60), while the most prevalent disease in premature newborn was hyperphenylalaninemia (50%, 3/6), respectively. The genetic analysis of 49 cases revealed 62 potentially pathogenic mutations in 10 well-documented pathogenic genes of IEMs, among which 21 were novel. In conclusion, differences in incidence and spectrum of full-term and premature births we obtained in NICU will provide diagnostic guidelines and therapeutic clues of neonatal IEMs for pediatricians.

The importance of anthropological methods in the diagnosis of rare diseases

Most of inborn errors of metabolism (IEMs) and rare endocrine-metabolic diseases (REMD) are rare diseases. According to the European Commission on Public Health, a rare disease is defined, based on its prevalence, as one affecting one in 2000 people. Many IEMs affect body stature, cause craniofacial abnormalities, and disturb the developmental process. Therefore, body proportion, dysmorphic characteristics, and morphological parameters must be assessed and closely monitored. This can be achieved only with the help of an anthropologist who has adequate tools. This is why the role of an anthropologist in collaboration with the physician in the diagnostic process is not to be underestimated. Clinical anthropologists contribute to assessing physical development and improve our understanding of the natural history of rare metabolic diseases. This paper presents anthropometric techniques and methods, such as analysis of demographic data, anthropometric parameters at birth, percentile charts, growth patterns, bioimpedance, somatometric profiles, craniofacial profiles, body proportion indices, and mathematical models of growth curves used in certain rare diseases. Contemporary anthropological methods play an important role in the diagnostic process of rare genetic diseases.

Neurometabolic Disorders of the Newborn

There is an extensive and diverse set of medical conditions affecting the neonatal brain within the spectrum of neurometabolic disorders. As such, their clinical presentations can be rather nonspecific, and can often mimic acquired entities such as hypoxic-ischemic encephalopathy and sepsis. Similarly, the radiological findings in these entities can also be frequently nonspecific, but a more detailed analysis of imaging findings (especially magnetic resonance imaging) alongside the relevant clinical details can be a rewarding experience, thus enabling a timely and targeted diagnosis. Early diagnosis of an underlying neurometabolic disorder is vital, as some of these entities are potentially treatable, and laboratory and genetic testing can be precisely targeted. Further, their detection helps with counselling families for future pregnancies. We present a review of neurometabolic disorders specific to the newborns with a focus on how neuroimaging findings match their clinical presentation patterns.

Contribution of tandem mass spectrometry to the diagnosis of lysosomal storage disorders

Tandem mass spectrometry (MS/MS) is a highly sensitive and specific technique. Thanks to the development of triple quadrupole analyzers, it is becoming more widely used in laboratories working in the field of inborn errors of metabolism. We review here the state of the art of this technique applied to the diagnosis of lysosomal storage disorders (LSDs) and how MS/MS has changed the diagnostic rationale in recent years. This fine technology brings more sensitive, specific, and reliable methods than the previous biochemical ones for the analysis of urinary glycosaminoglycans, oligosaccharides, and sialic acid. In sphingolipidoses, the quantification of urinary sphingolipids (globotriaosylceramide, sulfatides) is possible. The measurement of new plasmatic biomarkers such as oxysterols, bile acids, and lysosphingolipids allows the screening of many sphingolipidoses and related disorders (Niemann-Pick type C), replacing tedious biochemical techniques. Applied to amniotic fluid, a more reliable prenatal diagnosis or screening of LSDs is now available for fetuses presenting with antenatal manifestations. Applied to enzyme measurements, it allows high throughput assays for the screening of large populations, even newborn screening. The advent of this new method can modify the diagnostic rationale behind LSDs.

Non-immune fetal hydrops of metabolic origin: a case report and a review of the literature

Aim

To propose a diagnostic algorithm for non-immune fetal hydrops (NIFH) of metabolic origin based on a review of the literature and on the workup of a clinical case.

Background

The etiology of NIFH is complex and remains unexplained in 15%–25% of patients. The appropriate work up beyond an initial approach is still not well defined but it should include screening for metabolic conditions. Inborn errors of metabolism comprise a heterogeneous group of autosomal recessive rare inherited disorders, among which lysosomal storage disorder is the most common subtype.

Case description

We report a case of a 30-year-old pregnant, primiparous woman, referred to a tertiary hospital at 22 weeks of gestation because of a fetal hydrops. The second trimester obstetric ultrasound showed a hydrothorax and a large subcutaneous edema. At 30 weeks of gestation, the fetal health status deteriorated and a massive hepatomegaly was detected. The metabolic study of the amniotic fluid supernatant suggested a lysosomal disease. The ominous prognosis of the condition motivated the parents to opt for a termination of pregnancy. The autopsy study confirmed the existence of a metabolic disease.

Conclusion

The incidence of inborn errors of metabolism may be significantly higher in NIHF than reported previously. Consequently, an extensive investigation for the etiology of NIHF including the screening for metabolic disorders seems to be crucial for a definitive diagnosis.

Clinical relevance

Despite the lack of treatment options for the majority of these disorders, it is of great importance to follow an established workup, in order to identify the index case as soon as possible, as pregnancy management decisions and prenatal counselling in future pregnancies will depend on a more precise diagnosis.