Population differences in the polyalanine domain and 6 new mutations in HLXB9 in patients with Currarino syndrome

Currarino syndrome: a comprehensive genetic review of a rare congenital disorder

Background

The triad of a presacral mass, sacral agenesis and an anorectal anomaly constitutes the rare Currarino syndrome (CS), which is caused by dorsal–ventral patterning defects during embryonic development. The major causative CS gene is MNX1, encoding a homeobox protein.

Main body

In the majority of patients, CS occurs as an autosomal dominant trait; however, a female predominance observed, implies that CS may underlie an additional mode(s) of inheritance. Often, the diagnosis of CS is established solely by clinical findings, impacting a detailed analysis of the disease. Our combined data, evaluating more than 60 studies reporting patients with CS-associated mutations, revealed a slightly higher incidence rate in females with a female-to-male ratio of 1.39:1. Overall, MNX1 mutation analysis was successful in only 57.4% of all CS patients investigated, with no mutation detected in 7.7% of the familial and 68% of the sporadic patients. Our studies failed to detect the presence of an expressed MNX1 isoform that might explain at least some of these mutation-negative cases.

Conclusion

Aside from MNX1, other genes or regulatory regions may contribute to CS and we discuss several cytogenetic studies and whole-exome sequencing data that have implicated further loci/genes in its etiology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01799-0.

Novel MNX1 mutations and genotype-phenotype analysis of patients with Currarino syndrome

Background

Currarino syndrome (CS) is a specific complex of congenital caudal anomalies, including anorectal malformations, presacral mass and sacral anomalies. Mutations in the MNX1 gene are closely related to CS and occur in almost all familial cases and less than half of sporadic patients. We investigated the spectrum of MNX1 pathogenic variants and associated clinical features in Chinese patients with CS.

Results

Seventeen index patients from 16 families were recruited from 2015 to 2018. All patients were diagnosed with CS and treated at the Capital Institute of Pediatrics Affiliated Children’s Hospital. Genetic testing was applied to identify mutations in CS patients and their relatives by whole-exome sequencing and Sanger sequencing. Functional verification was performed for a recurrent noncanonical splice site variant in MNX1 with a minigene splicing assay. In 17 CS patients, 14 were complete CS and 3 were mild CS. Nine variants in MNX1 were identified in 11 patients, and these included two frameshift mutations (p.Leu223Leufs*61, p.X402Serfs*70), four nonsense mutations (p.Gly42X, p.Cys88X, p.Gln24X, p.Cys241X), one missense mutation (p.Trp288Leu), one splice region variant (c.691 + 3G > T) and one polyalanine polymorphism (p.Ala135insAlaAla). Seven of these nine variants have never been reported. Pathogenic MNX1 mutations were found in 100% (4/4) of familial and 46% (6/13) of sporadic patients.

Conclusion

Our study expanded the mutation spectrum of MNX1 and provided clinical and genetic analyses of seventeen CS patients from mainland China.

Spectrum of MNX1 Pathogenic Variants and Associated Clinical Features in Korean Patients with Currarino Syndrome

Background

The major genetic cause of Currarino syndrome (CS), a congenital malformation syndrome typically characterized by sacral agenesis, anorectal malformation, and presence of a pre-sacral mass, is known to be pathogenic variants in motor neuron and pancreas homeobox 1 (MNX1), which exist in almost all familial cases and 30% of sporadic cases. Less commonly, a large deletion or a complex rearrangement involving the 7q36 region is associated with CS. We investigated the spectrum of MNX1 pathogenic variants and associated clinical features in the Korean patients with CS.

Methods

We enrolled 25 patients with CS, including 24 sporadic cases and one familial case. Direct sequencing of MNX1 and multiplex ligation-dependent probe amplification were performed. We also analyzed clinical phenotypes and evaluated genotype-phenotype correlations.

Results

We identified six novel variants amongst a total of six null variants, one missense variant, and one large deletion. The null variants included four frameshift variants (p.Gly98Alafs^*124, p.Gly145Alafs^*77, p.Gly151Leufs^*67, and p.Ala216Profs^*5) and two nonsense variants (p.Tyr186^* and p.Gln212^*). The missense variant, p.Lys295Gln, was located in the highly-conserved homeobox domain and was predicted to be deleterious. A large deletion involving the 7q36 region was detected in one patient. Pathogenic variants in MNX1 were detected in 28% of all CS cases and 25% of sporadic cases. The clinical phenotype was variable in patients with and without pathogenic variants; no significant genotype-phenotype correlation was observed.

Conclusions

This study revealed the spectrum and phenotypic variability of MNX1 pathogenic variants in the Korean population.

Sacral agenesis: a pilot whole exome sequencing and copy number study

Background

Caudal regression syndrome (CRS) or sacral agenesis is a rare congenital disorder characterized by a constellation of congenital caudal anomalies affecting the caudal spine and spinal cord, the hindgut, the urogenital system, and the lower limbs. CRS is a complex condition, attributed to an abnormal development of the caudal mesoderm, likely caused by the effect of interacting genetic and environmental factors. A well-known risk factor is maternal type 1 diabetes.

Method

Whole exome sequencing and copy number variation (CNV) analyses were conducted on 4 Caucasian trios to identify de novo and inherited rare mutations.

Results

In this pilot study, exome sequencing and copy number variation (CNV) analyses implicate a number of candidate genes, including SPTBN5, MORN1, ZNF330, CLTCL1 and PDZD2. De novo mutations were found in SPTBN5, MORN1 and ZNF330 and inherited predicted damaging mutations in PDZD2 (homozygous) and CLTCL1 (compound heterozygous). Importantly, predicted damaging mutations in PTEN (heterozygous), in its direct regulator GLTSCR2 (compound heterozygous) and in VANGL1 (heterozygous) were identified. These genes had previously been linked with the CRS phenotype.

Two CNV deletions, one de novo (chr3q13.13) and one homozygous (chr8p23.2), were detected in one of our CRS patients. These deletions overlapped with CNVs previously reported in patients with similar phenotype.

Conclusion

Despite the genetic diversity and the complexity of the phenotype, this pilot study identified genetic features common across CRS patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-016-0359-2) contains supplementary material, which is available to authorized users.

Phenotype analysis impacts testing strategy in patients with Currarino syndrome

Currarino syndrome (OMIM 175450) presents with sacral, anorectal, and intraspinal anomalies and presacral meningocele or teratoma. Autosomal dominant loss-of-function mutations in the MNX1 gene cause nearly all familial and 30% of sporadic cases. Less frequently, a complex phenotype of Currarino syndrome can be caused by microdeletions of 7q containing MNX1. Here, we report one familial and three sporadic cases of Currarino syndrome. To determine the most efficient genetic testing approach for these patients, we have compared results from MNX1 sequencing, chromosomal microarray, and performed a literature search with analysis of genotype-phenotype correlation. Based on the relationship between the type of mutation (intragenic MNX1 mutations vs 7q microdeletion) and the presence of intellectual disability, growth retardation, facial dysmorphism, and associated malformations, we propose a testing algorithm. Patients with the classic Currarino triad of malformations but normal growth, intellect, and facial appearance should have MNX1 sequencing first, and only in the event of a normal result should the clinician proceed with chromosomal microarray testing. In contrast, if growth delay and/or facial dysmorphy and/or intellectual disability are present, chromosomal microarray should be the first method of choice for genetic testing.

Spinal cord malformations

Malformations of the spinal cord are one of the most frequent malformations. They should be clearly divided into two completely different families of malformations: open dysraphisms and occult dysraphisms. Open dysraphism mostly consists in myelomeningocele (MMC). Its incidence is 1/1000 live births with a wide variation. Folic acid supplementation has been shown to reduce its risk. In most cases, the diagnosis is done prenatally by serum screening and ultrasound and may lead to termination of pregnancy. In case of decision to continue pregnancy, surgical treatment must be achieved during the first days of life, and in 50 to 90% of cases, a ventricular shunt must be installed. The follow-up of these children must be continued throughout life looking for late complications (Chiari II and syringomyelia, vertebral problems, neuropathic bladder, tethered cord). Occult dysraphisms are a heterogeneous group of malformations. Lipomas (filum and conus) are the most frequent and their treatment remains controversial. Diastematomyelia, neurenteric cysts, dermal sinus, and more complex forms (Currarino syndrome) belong to this group. Most of them can and must be diagnosed prenatally or at birth by careful examination of the lower back for the cutaneous stigmata of the disease to decrease the risk of neurological, urological, or orthopedic permanent handicap.

A 5.8 kb deletion removing the entire MNX1 gene in a Norwegian family with Currarino syndrome

Currarino syndrome (CS) is a clinically variable disorder characterized by anorectal, sacral and presacral anomalies. It is associated with loss-of-function mutations in the motor neuron and pancreas homeobox 1 (MNX1) gene. Inheritance is autosomal dominant, expression variable and penetrance incomplete. We describe a Norwegian family with typical CS in which a heterozygous deletion removes the entire MNX1 gene but no other known genes. We also report MNX1 mutations in three other Norwegian families and confirm that the GCC12 repeat (c.373_375[12]) is a normal allelic variant. This work underscores the importance of dosage analysis of MNX1 when Sanger sequencing is negative.

Mutation analysis of the motor neuron and pancreas homeobox 1 (MNX1, former HLXB9) gene in Swedish patients with Currarino syndrome

BACKGROUND

Currarino syndrome (CS) is a triad consisting of partial sacral agenesis, presacral mass, and anorectal malformations, typically anal stenosis but the phenotype varies. The main cause of this monogenic disorder is mutations in the motor neuron and pancreas homeobox 1 gene. We describe the clinical and genetic findings in 4 unrelated Swedish cases with CS and their relatives.

METHODS

We performed mutation analysis of the motor neuron and pancreas homeobox 1 gene in 4 cases with CS by DNA sequence analysis as well as multiplex ligation-dependent probe amplification. In addition, array comparative genome hybridization was performed in 2 cases. Including relatives, totally, 14 individuals were analyzed.

RESULTS

We found 2 previously described mutations, 1 de novo nonsense mutation (p.Gln212X) and 1 maternally inherited frameshift mutation (p.Pro18ProfsX38). In the family with the frameshift mutation, we also detected the same maternally inherited mutation in 3 of the proband's 4 brothers, who displayed varying symptoms. All mutation carriers had presacral tumors, although 2 were asymptomatic.

CONCLUSION

Our findings emphasize the need for genetic counseling and mutation analysis in patients with CS to detect tumors early. It shows the importance of evaluation of the sacrum and the presacral region in patients with anal stenosis with or without funnel anus. Family members of index cases should be considered for evaluation even if they are asymptomatic.

Mitochondrial oxidative phosphorylation compensation may preserve vision in patients with OPA1-linked autosomal dominant optic atrophy

Autosomal Dominant Optic Atrophy (ADOA) is the most common inherited optic atrophy where vision impairment results from specific loss of retinal ganglion cells of the optic nerve. Around 60% of ADOA cases are linked to mutations in the OPA1 gene. OPA1 is a fission-fusion protein involved in mitochondrial inner membrane remodelling. ADOA presents with marked variation in clinical phenotype and varying degrees of vision loss, even among siblings carrying identical mutations in OPA1. To determine whether the degree of vision loss is associated with the level of mitochondrial impairment, we examined mitochondrial function in lymphoblast cell lines obtained from six large Australian OPA1-linked ADOA pedigrees. Comparing patients with severe vision loss (visual acuity [VA]<6/36) and patients with relatively preserved vision (VA>6/9) a clear defect in mitochondrial ATP synthesis and reduced respiration rates were observed in patients with poor vision. In addition, oxidative phosphorylation (OXPHOS) enzymology in ADOA patients with normal vision revealed increased complex II+III activity and levels of complex IV protein. These data suggest that OPA1 deficiency impairs OXPHOS efficiency, but compensation through increases in the distal complexes of the respiratory chain may preserve mitochondrial ATP production in patients who maintain normal vision. Identification of genetic variants that enable this response may provide novel therapeutic insights into OXPHOS compensation for preventing vision loss in optic neuropathies.

Microcephaly, sensorineural deafness and Currarino triad with duplication-deletion of distal 7q

Currarino syndrome (CS) is a peculiar form of caudal regression syndrome [also known as autosomal dominant sacral agenesis (OMIM no. 176450)] characterised by (1) partial absence of the sacrum with intact first sacral vertebra, (2) a pre-sacral mass and (3) anorectal anomalies (Currarino triad). We studied a 3-year-old girl with Currarino triad who had additional systemic features and performed array comparative genomic hybridisation to look for chromosomal abnormalities. This girl had the typical spectrum of anomalies of the CS including (a) partial sacral agenesis (hemisacrum with remnants of only sacral S1-S2 vertebrae and a residual S3 vertebral body) associated with complete coccygeal agenesis, (b) pre-intrasacral dermoid, (c) intra-dural lipoma, (d) ectopic anus and (e) tethered cord. She had, in addition, pre- and post-natal growth impairment (<3rd percentile), severe microcephaly (<-3 SD) with normal gyration pattern and lack of cortical thickening associated with a hypoplastic inferior vermis, facial dysmorphism, sensorineural deafness and decreased serum levels of IGF-1. A de novo 10.3-Mb duplication of 7q34-q35 and an 8.8-Mb deletion on 7q36 were identified in this patient. The Homeobox HLXB9 (CS) gene is contained within the deletion accounting for the CS phenotype including microcephaly. The spectrums of associated abnormalities in the IGF-1 deficiency growth retardation with sensorineural deafness and mental retardation syndrome (OMIM no. 608747) are discussed. To the best of our knowledge, this is the first reported case of a patient with distal 7q chromosomal imbalance and features of CS triad (including microcephaly) and the first documented case of a patient with normal gyration pattern microcephaly. The spectrum of associated anomalies in this newly recognised phenotype complex consists of growth failure, typical facial anomalies with additional (previously unreported) nervous system abnormalities (e.g. sensorineural deafness) and somatomedin C deficiency.

MNX1 (HLXB9) mutations in Currarino patients

PURPOSE

The combination of partial absence of the sacrum, anorectal anomalies, and presacral mass constitutes Currarino syndrome (CS), which is associated with mutations in MNX1 motor neuron and pancreas homeobox 1 (previously HLXB9). Here, we report on the MNX1 mutations found in a family segregating CS and in 3 sporadic CS patients, as well as on the clinical characteristics of the affected individuals.

METHODS

MNX1 mutations were identified by direct sequencing the coding regions, intron/exon boundaries of MNX1 in 5 CS Japanese family members and 3 Chinese sporadic cases and their parents.

RESULTS

There were 2 novel (P18PfsX37, R243W) and 2 previously described (W288G and IVS2 + 1G > A) mutations. These mutations were not found in 198 control individuals and are predicted to impair the functioning of the MNX1 protein.

CONCLUSIONS

The variability of the CS phenotype among related or unrelated patients bearing the same mutation advocates for differences in the genetic background of each individual and invokes the implication of additional CS susceptibility genes.

Currarino syndrome as an etiology of a neonatal Escherichia coli meningitis

We report the case of a 29-day-old baby girl in whom Escherichia coli meningitis led to the diagnosis of Currarino syndrome (CS) (OMIM 176450), an autosomal-dominant genetic disorder associated with sacral agenesis, anorectal malformation, presacral masses and spinal cord malformations. Her condition improved with antibiotics and early surgical treatment. A familial study identified other genetically related individuals with similar symptoms.

Clinical and genetic analysis of HLXB9 gene in Korean patients with Currarino syndrome

Currarino syndrome (CS) is a rare autosomal dominant disease that has been described as a triad of partial sacral agenesis, anorectal anomalies, and a presacral mass. Mutations in the HLXB9 gene have been suggested to be the genetic background of CS. In this study, sequence analysis of the HLXB9 gene was performed in two familial and two sporadic Korean patients showing the clinical features of CS, and two mutations in the HLXB9 gene were identified only in the two familial cases. One mutation (R295W) has been reported previously, and the other (H260_Q261delinsLELLELE) is novel. Consistent with previous observations, the phenotypic expression of the mutation carriers in the CS families varies from mild to severe, including the complete triad. This study confirms that familial CS patients in Korea have the same genetic background as other ethnicities and reaffirms the phenotype variability among CS patients with the same mutation.

Clinical features and HLXB9 gene mutation of a sporadic Chinese Currarino's syndrome case

BACKGROUND/PURPOSE

The Currarino's syndrome (CS), which is characterized by sacral bony anomalies, anorectal malformation, and a presacral mass, is associated with mutations of HLXB9 gene. The aim of this study was to clearly define the clinical manifestations and molecular anomalies of CS in China.

METHODS

We studied the medical history and clinical manifestations of a child with presacral mass. Genomic DNA was extracted from lymphocytes, and mutation analysis of the HLXB9 gene was conducted by using polymerase chain reaction and direct sequencing in the child and her parents.

RESULTS

A previously unreported heterozygous missense mutation of HLXB9 gene was detected in the child.

CONCLUSIONS

The HLXB9 gene mutation could take place in sporadic cases of CS without a typical hemisacrum.

Adult index patient with Currarino syndrome due to a novelHLXB9 mutation, c.336dupG (p.P113fsX224), presenting with Hirschsprung's disease, cephalgia, and lumbodynia

BACKGROUND

The symptom triad of autosomal dominant Currarino syndrome (CS; MIM #176450) consists of anorectal malformation, a sacral bone defect, and presacral masses. Mutations in the homeoboxHLXB9 gene have already been described in a subset of sacrococcygeal anomalies characterized by partial sacral agenesis.

CASE

We report a 28-year-old male patient with Currarino syndrome due to a heterozygous novel frame-shift mutation c.336dupG (p.P113fsX224) in the homeoboxHLXB9 gene.

CONCLUSIONS

Molecular diagnostics may be helpful in cases of Hirschsprung's disease accompanied by other symptoms suggestive for Currarino syndrome, since it can lead to major complications such as perianal sepsis, meningitis, and malignant transformation.