Genotype-phenotype correlation in ATAD3A deletions: not just of scientific relevance

Elevated cholesterol in ATAD3 mutants is a compensatory mechanism that leads to membrane cholesterol aggregation

Aberrant cholesterol metabolism causes neurological disease and neurodegeneration, and mitochondria have been linked to perturbed cholesterol homeostasis via the study of pathological mutations in the ATAD3 gene cluster. However, whether the cholesterol changes were compensatory or contributory to the disorder was unclear, and the effects on cell membranes and the wider cell were also unknown. Using patient-derived cells, we show that cholesterol perturbation is a conserved feature of pathological ATAD3 variants that is accompanied by an expanded lysosome population containing membrane whorls characteristic of lysosomal storage diseases. Lysosomes are also more numerous in Drosophila neural progenitor cells expressing mutant Atad3, which exhibit abundant membrane-bound cholesterol aggregates, many of which co-localize with lysosomes. By subjecting the Drosophila Atad3 mutant to nutrient restriction and cholesterol supplementation, we show that the mutant displays heightened cholesterol dependence. Collectively, these findings suggest that elevated cholesterol enhances tolerance to pathological ATAD3 variants; however, this comes at the cost of inducing cholesterol aggregation in membranes, which lysosomal clearance only partly mitigates.

"ATAD3C regulates ATAD3A assembly and function in the mitochondrial membrane"

Mitochondrial ATAD3A is an ATPase Associated with diverse cellular Activities (AAA) domain containing enzyme, involved in the structural organization of the inner mitochondrial membrane and of increasing importance in childhood disease. In humans, two ATAD3A paralogs arose by gene duplication during evolution: ATAD3B and ATAD3C. Here we investigate the cellular activities of the ATAD3C paralog that has been considered a pseudogene. We detected unique ATAD3C peptides in HEK 293T cells, with expression similar to that in human tissues, and showed that it is an integral membrane protein that exposes its carboxy-terminus to the intermembrane space. Overexpression of ATAD3C, but not of ATAD3A, in fibroblasts caused a decrease in cell proliferation and oxygen consumption rate, and an increase of cellular ROS. This was due to the incorporation of ATAD3C monomers in ATAD3A complex in the mitochondrial membrane reducing its size. Consistent with a negative regulation of ATAD3A function in mitochondrial membrane organization, ATAD3C expression led to increased accumulation of respiratory chain dimeric CIII in the inner membrane, to the detriment to that assembled in respiratory supercomplexes. Our results demonstrate a negative dominant role of the ATAD3C paralog with implications for mitochondrial OXPHOS function and suggest that its expression regulates ATAD3A in the cell.

Harel-Yoon syndrome caused by a novel variant in ATAD3A: A case report

Objectives

To describe the clinical feature of a very recently identified phenotype associated with ATAD3A variation.

Methods

A neonate with Harel-Yoon syndrome was identified. We describe the proband's clinical and radiological features. The affected newborn and her parents underwent whole-exome sequencing and PCR-Sanger sequencing.

Results

Previously reported clinical manifestations were rare in the neonatal period, including unmanageable seizures necessitating the use of multiple drugs, congenital laryngeal stridor, hypotonia, challenges with feeding, corneal opacity, and subsequent demise due to respiratory failure. Molecular investigations have unveiled the presence of a newly identified heterozygous single-base substitution (c.1517A > C; p.Q506P) within the ATAD3A gene.

Discussion

This study unveils a novel single-base substitution, thereby expanding the mutation spectrum associated with ATAD3A. Furthermore, the clinical characteristics exhibited during the neonatal phase are comprehensively described, potentially facilitating improved clinical recognition of ATAD3A-associated HAYOS.

Functional genomics and small molecules in mitochondrial neurodevelopmental disorders

Mitochondria are critical for brain development and homeostasis. Therefore, pathogenic variation in the mitochondrial or nuclear genome which disrupts mitochondrial function frequently results in developmental disorders and neurodegeneration at the organismal level. Large-scale application of genome-wide technologies to individuals with mitochondrial diseases has dramatically accelerated identification of mitochondrial disease-gene associations in humans. Multi-omic and high-throughput studies involving transcriptomics, proteomics, metabolomics, and saturation genome editing are providing deeper insights into the functional consequence of mitochondrial genomic variation. Integration of deep phenotypic and genomic data through allelic series continues to uncover novel mitochondrial functions and permit mitochondrial gene function dissection on an unprecedented scale. Finally, mitochondrial disease-gene associations illuminate disease mechanisms and thereby direct therapeutic strategies involving small molecules and RNA-DNA therapeutics. This review summarizes progress in functional genomics and small molecule therapeutics in mitochondrial neurodevelopmental disorders.

ATAD3A gene variations in a family with Harel-Yoon syndrome

An 11-day-old female neonate was admitted for cough with mouth foaming and feeding difficulties. The laboratory results indicated hyperlactatemia, elevated markers of myocardial injury and inflammation, and high levels of acylcarnitine octanoylcarnitine and decanoylcarnitine in tandem mass spectrometry. Ultrasonography and MRI suggested cardiac insufficiency and hypertrophic cardiomyopathy. Whole exome sequencing showed that both the proband and her elderly sister had a compound heterozygous variant of c.1492dup (p.T498Nfs*13) and c.1376T>C (p.F459S) in the ATAD3A gene, inherited from their father and mother, respectively. The diagnosis of Harel-Yoon syndrome was confirmed. The proband and her sister were born with clinical manifestations of metabolic acidosis, hyperlactatemia, feeding difficulties, elevated markers of myocardial injury as well as cardiac insufficiency, and both died in early infancy.

ATAD3A: A Key Regulator of Mitochondria-Associated Diseases

Mitochondrial membrane protein ATAD3A is a member of the AAA-domain-containing ATPases superfamily. It is important for the maintenance of mitochondrial DNA, structure, and function. In recent years, an increasing number of ATAD3A mutations have been identified in patients with neurological symptoms. Many of these mutations disrupt mitochondrial structure, function, and dynamics and are lethal to patients at a young age. Here, we summarize the current understanding of the relationship between ATAD3A and mitochondria, including the interaction of ATAD3A with mitochondrial DNA and mitochondrial/ER proteins, the regulation of ATAD3A in cholesterol mitochondrial trafficking, and the effect of known ATAD3A mutations on mitochondrial function. In the current review, we revealed that the oligomerization and interaction of ATAD3A with other mitochondrial/ER proteins are vital for its various functions. Despite affecting different domains of the protein, nearly all documented mutations observed in ATAD3A exhibit either loss-of-function or dominant-negative effects, potentially leading to disruption in the dimerization of ATAD3A; autophagy; mitophagy; alteration in mitochondrial number, size, and cristae morphology; and diminished activity of mitochondrial respiratory chain complexes I, IV, and V. These findings imply that ATAD3A plays a critical role in mitochondrial dynamics, which can be readily perturbed by ATAD3A mutation variants.

ATAD3A-related pontocerebellar hypoplasia: new patients and insights into phenotypic variability

BACKGROUND

Pathogenic variants in the ATAD3A gene lead to a heterogenous clinical picture and severity ranging from recessive neonatal-lethal pontocerebellar hypoplasia through milder dominant Harel-Yoon syndrome up to, again, neonatal-lethal but dominant cardiomyopathy. The genetic diagnostics of ATAD3A-related disorders is also challenging due to three paralogous genes in the ATAD3 locus, making it a difficult target for both sequencing and CNV analyses.

RESULTS

Here we report four individuals from two families with compound heterozygous p.Leu77Val and exon 3-4 deletion in the ATAD3A gene. One of these patients was characterized as having combined OXPHOS deficiency based on decreased complex IV activities, decreased complex IV, I, and V holoenzyme content, as well as decreased levels of COX2 and ATP5A subunits and decreased rate of mitochondrial proteosynthesis. All four reported patients shared a strikingly similar clinical picture to a previously reported patient with the p.Leu77Val variant in combination with a null allele. They presented with a less severe course of the disease and a longer lifespan than in the case of biallelic loss-of-function variants. This consistency of the phenotype in otherwise clinically heterogenous disorder led us to the hypothesis that the severity of the phenotype could depend on the severity of variant impact. To follow this rationale, we reviewed the published cases and sorted the recessive variants according to their impact predicted by their type and the severity of the disease in the patients.

CONCLUSION

The clinical picture and severity of ATAD3A-related disorders are homogenous in patients sharing the same combinations of variants. This knowledge enables deduction of variant impact severity based on known cases and allows more accurate prognosis estimation, as well as a better understanding of the ATAD3A function.

Ketogenic Diet Attenuates Refractory Epilepsy of Harel-Yoon Syndrome With ATAD3A Variants: A Case Report and Review of Literature

BACKGROUND

Harel-Yoon syndrome is a disease caused by variants in the ATAD3A gene, which manifest as global developmental delay, hypotonia, intellectual disability, and axonal neuropathy. The aim of this study is to summarize the clinical and gene mutation characteristics of a child with refractory epilepsy caused by ATAD3A gene mutation.

METHODS

The whole-exome sequencing combined with copy number variation analysis could help to understand the genetic diversity and underlying disease mechanisms in ATAD3A gene mutation.

RESULTS

We report a Chinese boy with Harel-Yoon syndrome presenting with refractory epilepsy, hypotonia, global developmental delay, and congenital cataract through whole-exome sequencing. Genetic analysis showed a missense mutation, c.251T>C(p.Thr84Met) in the ATAD3A gene (NM_001170535.1). Further copy number variation analysis identified a novel heterozygous deletion on chromosome1p36.33, which spans ATAD3A exon 1 and 2 regions. Multiple antiepileptic drugs failed to control his seizures. Eventually, seizure was controlled through ketogenic diet (KD).

CONCLUSION

Our case shows the potential diagnostic role of whole-exome sequencing in Harel-Yoon syndrome and expands the ATAD3A gene mutation spectrum. Multiple antiepileptic drugs failed to control refractory epilepsy in Harel-Yoon syndrome. The KD therapy may be effective for patients with refractory epilepsy who carry the ATAD3A variants.

Harel Yoon syndrome: a novel mutation in ATAD3A gene and expansion of the clinical spectrum

BACKGROUND

Harel-Yoon syndrome (HAYOS) is a recently described neurodevelopmental disorder characterized by psychomotor delay, truncal hypotonia, appendicular spasticity, and peripheral neuropathy. It is caused by mutations in ATAD3A gene located on chromosome 1p.36.33 whose functions include mitochondrial DNA stabilization, the regulation of mitochondrial fission/fusion, and cholesterol homeostasis.

MATERIALS AND METHODS

An 11-year-old male patient of consanguineous Egyptian parents, who present with neuroregression and ptosis along with progressive impaired vision, undergoes complete ophthalmological and neurological examination. Additionally, color fundus photography, fundus autofluorescence (FAF), spectral domain optical coherence tomography (SD-OCT) of both the macula and optic nerve head, full field electroretinogram (ERG), and visual field perimetry were obtained. Whole-exome sequencing and mitochondrial genome sequencing were done in a commercial laboratory from a peripheral blood sample.

RESULTS

A novel mutation in ATAD3A gene c.624_644del was identified by whole-exome sequencing consistent with a diagnosis of Harel-Yoon Syndrome (HAYOS). The 11-year-old boy had characteristic features of neurodevelopmental delay, hypotonia, and peripheral neuropathy. However, we documented some novel features as fatiguable ptosis, facial weakness, progressive bulbar palsy, obsessive-compulsive disorder (OCD) in addition to cone system dysfunction.

CONCLUSION

Our study reports a novel mutation in ATAD3A gene and expands the clinical spectrum of Harel-Yoon Syndrome. Future research aiming at better understanding of gene function will lead to better genotype-phenotype correlation and could pave the way to more treatment options.

Severe spinal cord hypoplasia due to a novel ATAD3A compound heterozygous deletion

Biallelic deletions extending into the ATPase family AAA-domain containing protein 3A (ATAD3A) gene lead to infantile lethality with severe pontocerebellar hypoplasia (PCH). However, only 12 such cases have been reported worldwide to date, and the genotype–phenotype correlations are not well understood. We describe cases associated with the same novel biallelic deletions of the ATAD3A and ATAD3B/3A regions in Japanese siblings with severe spinal cord hypoplasia and multiple malformations, including PCH, leading to neonatal death. The ATAD3A protein is essential for normal interaction between mitochondria and endoplasmic reticulum and is important for mitochondrial biosynthesis. The cases were evaluated using whole-genome sequencing for genetic diagnosis of mitochondrial disease. Spinal cord lesions associated with biallelic compound heterozygous deletion extending into the ATAD3A gene have not been reported. In addition, the ATAD3A deletion was 19 base pairs long, which is short compared with those reported previously. This deletion introduced a frameshift, resulting in a premature termination codon, and was expected to be a null allele. The pathological findings of the atrophic spinal cord showed gliosis and tissue destruction of the gray and white matter. We describe spinal cord lesions as a new central nervous system phenotype associated with a biallelic compound heterozygous deletion extending into the ATAD3A gene. Biallelic ATAD3A deletions should be considered in cases of mitochondrial disease with spinal cord hypoplasia and PCH.

Prenatal exome sequencing: A useful tool for the fetal neurologist

Prenatal exome sequencing (pES) is a promising tool for diagnosing genetic disorders when structural anomalies are detected on prenatal ultrasound. The aim of this study was to investigate the diagnostic yield and clinical impact of pES as an additional modality for fetal neurologists who counsel parents in case of congenital anomalies of the central nervous system (CNS). We assessed 20 pregnancies of 19 couples who were consecutively referred to the fetal neurologist for CNS anomalies. pES had a diagnostic yield of 53% (10/19) with most diagnosed pregnancies having agenesis or hypoplasia of the corpus callosum (7/10). Overall clinical impact was 63% (12/19), of which the pES result aided parental decision making in 55% of cases (6/11), guided perinatal management in 75% of cases (3/4), and was helpful in approving a late termination of pregnancy request in 75% of cases (3/4). Our data suggest that pES had a high diagnostic yield when CNS anomalies are present, although this study is limited by its small sample size. Moreover, pES had substantial clinical impact, which warrants implementation of pES in the routine care of the fetal neurologist in close collaboration with gynecologists and clinical geneticists.

Functional interpretation of ATAD3A variants in neuro-mitochondrial phenotypes

Background

ATPase family AAA-domain containing protein 3A (ATAD3A) is a nuclear-encoded mitochondrial membrane-anchored protein involved in diverse processes including mitochondrial dynamics, mitochondrial DNA organization, and cholesterol metabolism. Biallelic deletions (null), recessive missense variants (hypomorph), and heterozygous missense variants or duplications (antimorph) in ATAD3A lead to neurological syndromes in humans.

Methods

To expand the mutational spectrum of ATAD3A variants and to provide functional interpretation of missense alleles in trans to deletion alleles, we performed exome sequencing for identification of single nucleotide variants (SNVs) and copy number variants (CNVs) in ATAD3A in individuals with neurological and mitochondrial phenotypes. A Drosophila Atad3a Gal4 knockin-null allele was generated using CRISPR-Cas9 genome editing technology to aid the interpretation of variants.

Results

We report 13 individuals from 8 unrelated families with biallelic ATAD3A variants. The variants included four missense variants inherited in trans to loss-of-function alleles (p.(Leu77Val), p.(Phe50Leu), p.(Arg170Trp), p.(Gly236Val)), a homozygous missense variant p.(Arg327Pro), and a heterozygous non-frameshift indel p.(Lys568del). Affected individuals exhibited findings previously associated with ATAD3A pathogenic variation, including developmental delay, hypotonia, congenital cataracts, hypertrophic cardiomyopathy, and cerebellar atrophy. Drosophila studies indicated that Phe50Leu, Gly236Val, Arg327Pro, and Lys568del are severe loss-of-function alleles leading to early developmental lethality. Further, we showed that Phe50Leu, Gly236Val, and Arg327Pro cause neurogenesis defects. On the contrary, Leu77Val and Arg170Trp are partial loss-of-function alleles that cause progressive locomotion defects and whose expression leads to an increase in autophagy and mitophagy in adult muscles.

Conclusion

Our findings expand the allelic spectrum of ATAD3A variants and exemplify the use of a functional assay in Drosophila to aid variant interpretation.

Mitochondrial Diseases: A Diagnostic Revolution

Mitochondrial disorders have emerged as a common cause of inherited disease, but are traditionally viewed as being difficult to diagnose clinically, and even more difficult to comprehensively characterize at the molecular level. However, new sequencing approaches, particularly whole-genome sequencing (WGS), have dramatically changed the landscape. The combined analysis of nuclear and mitochondrial DNA (mtDNA) allows rapid diagnosis for the vast majority of patients, but new challenges have emerged. We review recent discoveries that will benefit patients and families, and highlight emerging questions that remain to be resolved.

Mitochondrial dysfunction caused by novel ATAD3A mutations

Mitochondrial respiratory chain integrity depends on a number of proteins encoded by nuclear and mitochondrial genomes. Mutations of such factors can result in isolated or combined respiratory chain deficits, some of which can induce abnormal morphology of the mitochondrial network or accumulation of intermediary metabolites. Consequently, affected patients are clinically heterogeneous, presenting with central nervous system, muscular, or neurodegenerative disorders. ATAD3A is a nuclear-encoded ATPase protein of the AAA+ family and has been localized to the inner mitochondrial membrane. Recently reported mutations or large deletions in the ATDA3A gene in patients have been shown to induce altered mitochondrial structure and function and abnormal cholesterol metabolism in a recessive or dominant manner. Here, we report two siblings presenting axonal sensory-motor neuropathy associated with neonatal cataract. Genetic analyses identified two novel mutations in ATAD3A; a point mutation and an intronic 15 bp deletion affecting splicing and leading to exon skipping. Biochemical analysis in patient cells and tissues showed abnormal function of the mitochondrial respiratory chain in muscle and abnormal mitochondrial cristae structure. These new cases underline the large spectrum of biochemical and clinical presentations of ATAD3A deficiency and the different modes of inheritance, making it an atypical mitochondrial disorder.

Fatal perinatal mitochondrial cardiac failure caused by recurrent de novo duplications in the ATAD3 locus

Background

In about half of all patients with a suspected monogenic disease, genomic investigations fail to identify the diagnosis. A contributing factor is the difficulty with repetitive regions of the genome, such as those generated by segmental duplications. The ATAD3 locus is one such region, in which recessive deletions and dominant duplications have recently been reported to cause lethal perinatal mitochondrial diseases characterized by pontocerebellar hypoplasia or cardiomyopathy, respectively.

Methods

Whole exome, whole genome and long-read DNA sequencing techniques combined with studies of RNA and quantitative proteomics were used to investigate 17 subjects from 16 unrelated families with suspected mitochondrial disease.

Findings

We report six different de novo duplications in the ATAD3 gene locus causing a distinctive presentation including lethal perinatal cardiomyopathy, persistent hyperlactacidemia, and frequently corneal clouding or cataracts and encephalopathy. The recurrent 68 Kb ATAD3 duplications are identifiable from genome and exome sequencing but usually missed by microarrays. The ATAD3 duplications result in the formation of identical chimeric ATAD3A/ATAD3C proteins, altered ATAD3 complexes and a striking reduction in mitochondrial oxidative phosphorylation complex I and its activity in heart tissue.

Conclusions

ATAD3 duplications appear to act in a dominant-negative manner and the de novo inheritance infers a low recurrence risk for families, unlike most pediatric mitochondrial diseases. More than 350 genes underlie mitochondrial diseases. In our experience the ATAD3 locus is now one of the five most common causes of nuclear-encoded pediatric mitochondrial disease but the repetitive nature of the locus means ATAD3 diagnoses may be frequently missed by current genomic strategies.

Funding

Australian NHMRC, US Department of Defense, Japanese AMED and JSPS agencies, Australian Genomics Health Alliance and Australian Mito Foundation.

Recurrent De Novo NAHR Reciprocal Duplications in the ATAD3 Gene Cluster Cause a Neurogenetic Trait with Perturbed Cholesterol and Mitochondrial Metabolism

Recent studies have identified both recessive and dominant forms of mitochondrial disease that result from ATAD3A variants. The recessive form includes subjects with biallelic deletions mediated by non-allelic homologous recombination. We report five unrelated neonates with a lethal metabolic disorder characterized by cardiomyopathy, corneal opacities, encephalopathy, hypotonia, and seizures in whom a monoallelic reciprocal duplication at the ATAD3 locus was identified. Analysis of the breakpoint junction fragment indicated that these 67 kb heterozygous duplications were likely mediated by non-allelic homologous recombination at regions of high sequence identity in ATAD3A exon 11 and ATAD3C exon 7. At the recombinant junction, the duplication allele produces a fusion gene derived from ATAD3A and ATAD3C, the protein product of which lacks key functional residues. Analysis of fibroblasts derived from two affected individuals shows that the fusion gene product is expressed and stable. These cells display perturbed cholesterol and mitochondrial DNA organization similar to that observed for individuals with severe ATAD3A deficiency. We hypothesize that the fusion protein acts through a dominant-negative mechanism to cause this fatal mitochondrial disorder. Our data delineate a molecular diagnosis for this disorder, extend the clinical spectrum associated with structural variation at the ATAD3 locus, and identify a third mutational mechanism for ATAD3 gene cluster variants. These results further affirm structural variant mutagenesis mechanisms in sporadic disease traits, emphasize the importance of copy number analysis in molecular genomic diagnosis, and highlight some of the challenges of detecting and interpreting clinically relevant rare gene rearrangements from next-generation sequencing data.

Novel ATAD3A recessive mutation associated to fatal cerebellar hypoplasia with multiorgan involvement and mitochondrial structural abnormalities

Lethal neonatal encephalopathies are heterogeneous congenital disorders that can be caused by mitochondrial dysfunction. Biallelic large deletions in the contiguous ATAD3B and ATAD3A genes, encoding mitochondrial inner membrane ATPases of unknown function, as well as compound heterozygous nonsense and missense mutations in the ATAD3A gene have been recently associated with fatal neonatal cerebellar hypoplasia. In this work, whole exome sequencing (WES) identified the novel homozygous variant c.1217 T > G in ATAD3A, predicting a p.(Leu406Arg) substitution, in four siblings from a consanguineous family presenting with fatal neonatal cerebellar hypoplasia, seizures, axial hypotonia, hypertrophic cardiomyopathy, hepatomegaly, congenital cataract, and dysmorphic facies. Biochemical phenotypes of the patients included hyperlactatemia and hypocholesterolemia. Healthy siblings and parents were heterozygous for this variant, which is predicted to introduce a polar chain within the catalytic domain of ATAD3A that shortens its beta-sheet structure, presumably affecting protein stability. Accordingly, patient's fibroblasts with the homozygous variant displayed a specific reduction in ATAD3A protein levels associated with profound ultrastructural alterations of mitochondrial cristae and morphology. Our findings exclude the causative role of ATAD3B on this severe phenotype, expand the phenotypical spectrum of ATAD3A pathogenic variants and emphasize the vital role of ATAD3A in mitochondrial biogenesis.

From diagnostic yield to clinical impact: a pilot study on the implementation of prenatal exome sequencing in routine care

PURPOSE

Exome sequencing (ES) is an efficient tool to diagnose genetic disorders postnatally. Recent studies show that it may have a considerable diagnostic yield in fetuses with structural anomalies on ultrasound. We report on the clinical impact of the implementation of prenatal ES (pES) for ongoing pregnancies in routine care.

METHODS

We retrospectively analyzed the impact of pES on pregnancy outcome and pre- or perinatal management in the first 22 patients counseled for pES because of one or more structural anomalies on fetal ultrasound.

RESULTS

In two cases, a diagnosis was made by chromosomal microarray analysis after ES counseling. The remaining 20 cases were divided in three groups: (1) pES to aid parental decision making (n = 12), (2) pES in the context of late pregnancy termination requests (n = 5), and (3) pES to guide pre- or perinatal management (n = 3). pES had a clinical impact in 75% (9/12), 40% (2/5), and 100% (3/3) respectively, showing an overall clinical impact of pES of 70% (14/20).

CONCLUSION

We show that clinical implementation of pES is feasible and affects parental decision making or pre- and perinatal management supporting further implementation of ES in the prenatal setting.

Putting genome-wide sequencing in neonates into perspective

PURPOSE

Several studies have reported diagnostic yields up to 57% for rapid exome or genome sequencing (rES/GS) as a single test in neonatal intensive care unit (NICU) patients, but the additional yield of rES/GS compared with other available diagnostic options still remains unquantified in this population.

METHODS

We retrospectively evaluated all genetic NICU consultations in a 2-year period.

RESULTS

In 132 retrospectively evaluated NICU consultations 27 of 32 diagnoses (84.4%) were made using standard genetic workup. Most diagnoses (65.6%) were made within 16 days. Diagnostic ES yield was 5/29 (17.2%). Genetic diagnoses had a direct effect on clinical management in 90.6% (29/32) of patients.

CONCLUSIONS

Our study shows that exome sequencing has a place in NICU diagnostics, but given the associated costs and the high yield of alternative diagnostic strategies, we recommend to first perform clinical genetic consultation.

What's new in pontocerebellar hypoplasia? An update on genes and subtypes

Background

Pontocerebellar hypoplasia (PCH) describes a rare, heterogeneous group of neurodegenerative disorders mainly with a prenatal onset. Patients have severe hypoplasia or atrophy of cerebellum and pons, with variable involvement of supratentorial structures, motor and cognitive impairments. Based on distinct clinical features and genetic causes, current classification comprises 11 types of PCH.

Main text

In this review we describe the clinical, neuroradiological and genetic characteristics of the different PCH subtypes, summarize the differential diagnosis and reflect on potential disease mechanisms in PCH. Seventeen PCH-related genes are now listed in the OMIM database, most of them have a function in RNA processing or translation. It is unknown why defects in these apparently ubiquitous processes result in a brain-specific phenotype.

Conclusions

Many new PCH related genes and phenotypes have been described due to the appliance of next generation sequencing techniques. By including such a broad range of phenotypes, including non-degenerative and postnatal onset disorders, the current classification gives rise to confusion. Despite the discovery of new pathways involved in PCH, treatment is still symptomatic. However, correct diagnosis of PCH is important to provide suitable care and counseling regarding prognosis, and offer appropriate (prenatal) genetic testing to families.