Otopathology in Kleefstra Syndrome: A Case Report

Highlighting cardiovascular manifestations of kleefstra syndrome: literature review and clinical insights

Kleefstra syndrome (KLEFS1) is a rare genetic disorder primarily caused by the deletion of the chromosome 9q34.3 genomic segment or pathogenic mutations in the euchromatin histone methyltransferase 1 (EHMT1) gene. It is characterized by intellectual disability or impairment, childhood hypotonia, and distinct facial features. Notably, cardiovascular defects especially congenital heart diseases also represent a major feature of KLEFS1. While the neuropsychiatric aspects of KLEFS1 have been extensively documented and researched, the cardiovascular manifestations have not received adequate attention. The majority of KLEFS1 patients often present with a spectrum of cardiovascular defects, including abnormal cardiac structure, arrhythmias, valve abnormalities, cardiomyopathy, and coronary artery abnormalities. Here, we systematically searched and reviewed previously published articles and case reports related to KLEFS1, conducting a comprehensive analysis of the existing literature to highlight the cardiovascular manifestations of this genetic disorder and explore the potential correlations between the cardiac phenotype and KLEFS1. Clinical trial number: Not applicable.

Clinical characteristics and genetic analysis of four pediatric patients with Kleefstra syndrome

BACKGROUND

Kleefstra syndrome spectrum (KLEFS) is an autosomal dominant disorder that can lead to intellectual disability and autism spectrum disorders. KLEFS encompasses Kleefstra syndrome-1 (KLEFS1) and Kleefstra syndrome-2 (KLEFS2), with KLEFS1 accounting for more than 75%. However, limited information is available regarding KLEFS2. KLEFS1 is caused by a subtelomeric chromosomal abnormality resulting in either deletion at the end of the long arm of chromosome 9, which contains the EHMT1 gene, or by variants in the EHMT1 gene and the KMT2C gene that cause KLEFS2.

METHODS

This study was a retrospective analysis of clinical data from four patients with KLEFS. Exome sequencing (ES) and Sanger sequencing techniques were used to identify and validate the candidate variants, facilitating the analysis of genotype‒phenotype correlations of the EHMT1 and KMT2C genes. Protein structure modeling was performed to evaluate the effects of the variants on the protein's three-dimensional structure. In addition, real-time quantitative reverse transcription‒polymerase chain reaction (RT‒qPCR) and western blotting were used to examine the protein and mRNA levels of the KMT2C gene.

RESULTS

Two patients with KLEFS1 were identified: one with a novel variant (c.2382 + 1G > T) and the other with a previously reported variant (c.2426 C > T, p.Pro809Leu) in the EHMT1 gene. A De novo deletion at the end of the long arm of chromosome 9 was also reported. Furthermore, a patient with KLEFS2 was identified with a novel variant in the KMT2C gene (c.568 C > T, p.Arg190Ter). The RT‒qPCR and western blot results revealed that the expression of the KMT2C gene was downregulated in the KLEFS2 sample.

CONCLUSION

This study contributes to the understanding of both KLEFS1 and KLEFS2 by identifying novel variants in EHMT1 and KMT2C genes, thereby expanding the variant spectrum. Additionally, we provide the first evidence of how a KMT2C variant leads to decreased gene and protein expression, enhancing our understanding of the molecular mechanisms underlying KLEFS2. Based on these findings, children exhibiting developmental delay, hypotonia, distinctive facial features, and other neurodevelopmental abnormalities should be considered for ES to ensure early intervention and treatment.

The first Brazilian clinical report of Kleefstra syndrome, including semicircular canals agenesis as a possible phenotype expansion

OBJECTIVE

to report the first case series of Brazilian children diagnosed with Kleefstra syndrome, present a possible phenotype expansion to the syndrome and to raise physicians' awareness for this rare disease.

RESULTS

seven patients with confirmed KS were evaluated, including 5 males and 2 females. Abnormal prenatal findings were observed in 4 patients. Most patients were born at term, with normal birth measurements. All patients had neurodevelopmental delay and 6 evolved with intellectual disability. Hearing loss was present in 57.1% of patients and 28.7% had congenital heart disease. In males, cryptorchidism was present in 75%. Despite the facial dysmorphisms, only 2 out of 7 patients had a pre-test clinical suspicion of KS. One specific patient presented bilateral agenesis of the semicircular canals, a very rare ear manifestation in Kleefstra syndrome, representing a possible phenotype expansion of the syndrome.

CONCLUSION

this report aims to promote awareness among physicians evaluating patients in a context of neurodevelopmental delay or congenital malformations, especially congenital heart defects. We also highlight a possible phenotype expansion of the syndrome, with a case of semicircular anomaly, not reported in this syndrome so far.

Incomplete Partition Type II Cochlear Malformations: Delineating the Three-Dimensional Structure from Digitized Human Histopathological Specimens

HYPOTHESIS

There are clinically relevant differences in scalae anatomy and spiral ganglion neuron (SGN) quantity between incomplete partition type II (IP-II) and normal cochleae.

BACKGROUND

IP-II is a commonly implanted cochlear malformation. Detailed knowledge of intracochlear three-dimensional (3D) morphology may assist with cochlear implant (CI) electrode selection/design and enable optimization of audiologic programming based on SGN maps.

METHODS

IP-II (n = 11) human temporal bone histological specimens were identified from the National Institute on Deafness and Other Communication Disorders National Temporal Bone Registry and digitized. The cochlear duct, scalae, and surgically relevant anatomy were reconstructed in 3D. A machine learning algorithm was applied to map the location and number of SGNs.

RESULTS

3D scalae morphology of the basal turn was normal. Scala tympani (ST) remained isolated for 540 degrees before fusing with scala vestibuli. Mean ST volume reduced below 1 mm 2 after the first 340 degrees. Scala media was a distinct endolymphatic compartment throughout; mean ± standard deviation cochlear duct length was 28 ± 3 mm. SGNs were reduced compared with age-matched norms (mean, 48%; range, 5-90%). In some cases, SGNs failed to ascend Rosenthal's canal, remaining in an abnormal basalward modiolar location. Two forms of IP-II were seen: type A and type B. A majority (98-100%) of SGNs were located in the basal modiolus in type B IP-II, compared with 76 to 85% in type A.

CONCLUSION

Hallmark features of IP-II cochleae include the following: 1) fusion of the ST and scala vestibuli at a mean of 540 degrees, 2) highly variable and overall reduced SGN quantity compared with normative controls, and 3) abnormal SGN distribution with cell bodies failing to ascend Rosenthal's canal.

Kleefstra syndrome: Recurrence in siblings due to a paternal mosaic mutation

Kleefstra syndrome (KS) is a rare autosomic dominant genetic disorder caused by euchromatic histone methyltransferase 1 (EHMT1) alterations. Patients mainly present with moderate to severe intellectual disability, a severe delay in/or absence of speech, autism spectrum disorder, childhood hypotonia, neuropsychiatric anomalies, and distinctive dysmorphic features. Here, we report the cases of a male and a female, two younger siblings of three, with asymptomatic parents. An EHMT1 new mutation was identified. Both presented with a typical core phenotype. Some specific features were noted, such as macrocephaly (previously reported) and enuresis (not yet described). Parental analysis identified the mutation in the mosaic state in the father. Reverse phenotyping enabled us to highlight the pauci phenotype features of inguinal hernia, azoospermia, and possible behavioral disorders. This allowed us to adapt his follow-up and genetic counseling for the family. Our three reported cases provide a new description of KS with an intragenic EHMT1 mutation, whereas in the literature most reported cases have EHMT1 deletions. Moreover, in the areas of next-generation sequencing and trio techniques with parental segregation, it is important to remain cautious about disregarding variants based on an autosomal recessive hypothesis.