Prenatal diagnosis of genetic renal diseases: breaking the code

Fetal hyperechoic kidneys: Diagnostic considerations and genetic testing strategies

Isolated bilateral hyperechoic kidneys (HEK) on prenatal ultrasound presents diagnostic, prognostic, and counseling challenges. Prognosis ranges from normal outcome to lethal postnatally. Presence/absence of extra-renal malformations, gestational age at presentation, amniotic fluid volume, and renal size may distinguish underlying etiologies and thereby prognosis, as prognosis is highly dependent upon underlying etiology. An underlying genetic diagnosis, clearly impactful, is determined in only 55%-60% of cases. We conducted a literature review of chromosomal (aneuploidies, copy number variants [CNVs]) single genes and other etiologies of fetal bilateral HEK, summarized how this information informs prognosis and recurrence risk, and critically assessed laboratory testing strategies. The most commonly identified etiologies are autosomal recessive and autosomal dominant polycystic kidney disease and microdeletions at 17q12 involving HNF1b. With rapid gene discovery, alongside advances in prenatal imaging and fetal phenotyping, the growing list of single gene diagnoses includes ciliopathies, overgrowth syndromes, and renal tubular dysgenesis. At present, microarray and gene panels or whole exome sequencing (WES) are first line tests employed for diagnostic evaluation. Whole genome sequencing (WGS), with the ability to detect both single nucleotide variants (SNVs) and CNVs, would be expected to provide the highest diagnostic yield.

Autosomal Recessive Polycystic Kidney Disease-The Clinical Aspects and Diagnostic Challenges

Autosomal recessive polycystic kidney disease (ARPKD) is one of the most common ciliopathies with kidney (nephromegaly, hypertension, renal dysfunction) and liver involvement (congenital hepatic fibrosis, dilated bile ducts). Clinical features also include growth failure and neurocognitive impairment. Plurality of clinical aspects requires multidisciplinary approach to treatment and care of patients. Until recently, diagnosis was based on clinical criteria. Results of genetic testing show the molecular basis of polycystic kidneys disease is heterogeneous, and differential diagnosis is essential. The aim of the article is to discuss the role of genetic testing and its difficulties in diagnostics of ARPKD in children.

Renal cystic disease and associated ciliopathies

PURPOSE OF REVIEW

To review disorders that are associated with renal cystic disease during prenatal life and to highlight the strong association between renal cystic disease and ciliopathies.

RECENT FINDINGS

There are numerous causative genes for ciliopathies that can present with cystic kidney disease. In the group of single gene ciliopathies, autosomal dominant polycystic kidney disease is by far the most prevalent one. Other examples are autosomal recessive polycystic kidney disease, nephronophthisis, Bardet-Biedl syndrome, Meckel-Gruber syndrome, Joubert syndrome and related disorders as well as X-linked orofaciodigital syndrome type 1, respectively. The prevalence of these inherited disorders sums up to about in 1 : 2000 people. These disorders with their hepatorenal fibrocystic character should be classified as multisystem diseases.

SUMMARY

Understanding of the origin of renal cystic disease and associated disorders is important to make the appropriate prenatal diagnosis and for counseling affected parents. In the future, understanding of the pathophysiology may help to develop new treatment strategies.

Disorders of fatty acid oxidation and autosomal recessive polycystic kidney disease-different clinical entities and comparable perinatal renal abnormalities

BACKGROUND

Differential diagnosis of prenatally detected hyperechogenic and enlarged kidneys can be challenging as there is a broad phenotypic overlap between several rare genetic and non-genetic disorders. Metabolic diseases are among the rarest underlying disorders, but they demand particular attention as their prognosis and postnatal management differ from those of other diseases.

METHODS

We report two cases of cystic, hyperechogenic and enlarged kidneys detected on prenatal ultrasound images, resulting in the suspected diagnosis of autosomal recessive polycystic kidney disease (ARPKD). Postnatal clinical course and work-up, however, revealed early, neonatal forms of disorders of fatty acid oxidation (DFAO) in both cases, namely, glutaric acidemia type II, based on identification of the novel, homozygous splice-site mutation c.1117-2A > G in the ETFDH gene, in one case and carnitine palmitoyltransferase II deficiency in the other case.

RESULTS

Review of pre- and postnatal sonographic findings resulted in the identification of some important differences that might help to differentiate DFAO from ARPKD. In DFAO, kidneys are enlarged to a milder degree than in ARPKD, and the cysts are located ubiquitously, including also in the cortex and the subcapsular area. Interestingly, recent studies have pointed to a switch in metabolic homeostasis, referred to as the Warburg effect (aerobic glycolysis), as one of the underlying mechanisms of cell proliferation and cyst formation in cystic kidney disease. DFAO are characterized by the inhibition of oxidative phosphorylation, resulting in aerobic glycolysis, and thus they do resemble the Warburg effect. We therefore speculate that this inhibition might be one of the pathomechanisms of renal hyperproliferation and cyst formation in DFAO analogous to the reported findings in ARPKD.

CONCLUSIONS

Neonatal forms of DFAO can be differentially diagnosed in neonates with cystic or hyperechogenic kidneys and necessitate immediate biochemical work-up to provide early metabolic management.

Antenatal manifestations of inborn errors of metabolism: prenatal imaging findings

Prenatal manifestations of inborn errors of metabolism (IEM) are related to severe disorders involving metabolic pathways active in the fetal period and not compensated by maternal or placental metabolism. Some prenatal imaging findings can be suggestive of such conditions-especially in cases of consanguinity and/or recurrence of symptoms-after exclusion of the most frequent nonmetabolic etiologies. Most of these prenatal imaging findings are nonspecific. They include mainly ascites and hydrops fetalis, intrauterine growth restriction (IUGR), central nervous system (CNS) anomalies, echogenic kidneys, epiphyseal stippling, craniosynostosis, and a wide spectrum of dysostoses. These anomalies can be isolated, but in most cases, an IEM is suggested by an association of features. It must be stressed that the diagnosis of an IEM in the prenatal period is based on a close collaboration between specialists in fetal imaging, medicine, genetics, biology, and pathology.

Fetal Kidneys Ultrasound Appearance in the First Trimester - Clinical Significance and Limits of Counseling

OBJECTIVE

The objective of this study was to determine the visualizing rate of fetal kidneys at various gestational ages in late first trimester (FT) and to establish the clinical significance of their two-dimensional ultrasound (2DUS) appearance in the FT.

METHODS

In a prospective cross-sectional study, 1456 women from an unselected population underwent a detailed assessment of fetal anatomy at 11+0 -13+4 weeks of gestation with the use of transabdominal sonography. Information on the ultrasound findings, antenatal course and perinatal outcome was obtained in 1331 cases.

RESULTS

44 cases in which a congenital kidney disease was detected by ultrasound in the prenatal period were identified. The renal pathology was suspected in the FT in 8 cases, and confirmed by a standard test (postmortem autopsy or second-trimester scan) in 4 cases. The standard detailed second-trimester scan at 18-22 weeks diagnosed another 23 cases but refuted suspicion in 4 FT positive cases. The third trimester added another 17, all confirmed by the postpartum scan. For FT presence or absence of congenital renal anomalies, sensitivity, specificity, +LRs and -LRs of 2DUS were 9.09%, 99.69%, 29.25, and 0.91.

CONCLUSION

FT prenatal kidneys' visualization is critically dependent on the gestational age. FT diagnosis holds uncertainty. An early diagnosis carries a risk of providing a false-positive or a false-negative result, because the differentiation of the renal system is delayed or the diagnosis is not amenable yet to prenatal ultrasound. No FT findings can exclude the mid-trimester follow-up ultrasound scan. Second and third trimester scan are relevant for congenital kidney diseases.

A rare case of renal dysplasia: prenatal and postnatal management

The ultrasonographic detection of renal anomalies may modify obstetric management and facilitate pediatric care of the newborn. We performed prenatal differential diagnosis of an isolated unilateral cystic renal mass (71 × 74 × 82 mm) in a pregnant woman at 26 weeks of gestation. No other abnormalities were detected by ultrasonography, except for polyhydramnios. Repeated percutaneous cyst aspirations were required because of the increasing risk of vital organ damage. Postnatal nephroureterectomy was performed. Anatomopathologic analysis led to the diagnosis of segmental renal dysplasia, which could not be included in any of the four groups of Potter's classification of cystic renal dysplasia.

The diagnostic value of ultrasound in cystic kidney diseases

Renal cysts in childhood can be found in a variety of diseases, which can be congenital or acquired, or renal cysts may be part of a multiorgan disease or restricted to the kidneys only. Ultrasonography is the first-line diagnostic tool and is informative in many cases. However, there is a broad spectrum in the sonographic appearance of renal cysts, and family or genetic studies, a search for extrarenal organ involvement, or additional imaging modalities may be required to make a definitive diagnosis. The aim of this article is to summarize the diagnostic potential and limitations of ultrasonography and depict typical examples of the most important cystic entities.

Prenatal MRI findings of polycystic kidney disease associated with holoprosencephaly

Holoprosencephaly (HPE) and polycystic kidney disease (PKD) are genetically heterogeneous anomalies which can make up part of various syndromes or chromosomal anomalies. Due to the rapid lethality prognosis, early and precise prenatal diagnosis would be of great value. This case report describes extensive PKD involvement, already present in utero, in a patient with HPE and subdural effusion visible by MR imaging. The detailed anatomic information obtained by the MR imaging can guide the surgical planning and can aid antenatal counseling.

Unusual sonographic features of ARPKD

The classic sonographic appearance of the kidneys in fetuses with autosomal recessive polycystic kidney disease (ARPKD) has been well described. We report a case of enlarged kidneys with pyramidal hyperechogenicity quite similar to medullary nephrocalcinosis found in a fetus at 34 weeks' gestation. At 39 weeks, a female neonate was delivered and died after 22 h due to pulmonary insufficiency secondary to severe oligohydramnios. On pathological analysis, the gross and microscopic findings were typical of ARPKD with diffuse dilatation of tubules throughout. The fetal renal lobulation was prominent and on section, the pyramids were delineated within each lobule, accounting for the clear image of the pyramids observed on sonography.

Familial diseases revealed by a fetal anomaly

OBJECTIVES

The recognition of a fetal anomaly can lead to the same diagnosis being made in one of the asymptomatic parents unaware of the problem. We analyzed cases in which the discovery of a fetal anomaly led to the discovery of a genetic familial disorder.

METHODS

Families in which the recognition of a fetal anomaly led to the same diagnosis being made in one of the asymptomatic parents were included.

RESULTS

Twenty couples were included in the study. The fetal anomalies were cleft lip and palate (4), cardiac anomalies (2), cerebral anomalies (1), bilateral club feet with polyhydramnios, akinesia or camptodactily (5), nuchal anomalies (2), micromelia (3), polydactyly (2), and limited elbow extension (1). Genetic counselling helped establish nine maternal diseases as follows: Steinert disease (3), spinal muscular atrophy (1), antecubital pterygium (1), DiGeorge (1), Wardenburg type II (1), Charge (1) and Greig syndromes (1). Eleven paternal diseases were discovered, which were Noonan-like syndrome (1), paternal cervical anomalies (1), Goldenhar syndrome (1), dominant autosomal arthrogryposis (1), osteogenesis imperfecta (3), tuberous sclerosis (1), dominant transposition of great vessels (1), Weyers acrofacial dysostosis (1), and autosomal dominant holoprosencephaly (1). Twelve couples continued with pregnancy and eight opted for termination of pregnancy.

CONCLUSION

The fetus is central in giving the first insight into a familial disorder. It can reveal familial diseases undiscovered in the parent and help understand the mode of transmission of an anomaly, mainly the autosomal dominant diseases with variable expressions.