Chromosome 15q BP3 to BP5 deletion is a likely locus for speech delay and language impairment: Report on a four-member family and an unrelated boy

Deciphering the genetic basis of developmental language disorder in children without intellectual disability, autism or apraxia of speech

BACKGROUND

Developmental language disorder (DLD) refers to children who present with language difficulties that are not due to a known biomedical condition or associated with autism spectrum disorder (ASD) or intellectual disability (ID). The clinical heterogeneity of language disorders, the frequent presence of comorbidities, and the inconsistent terminology used over the years have impeded both research and clinical practice. Identifying sub-groups of children (i.e. DLD cases without childhood apraxia of speech (CAS)) with language difficulties is essential for elucidating the underlying genetic causes of this condition. DLD presents along a spectrum of severity, ranging from mild speech delays to profound disturbances in oral language structure in otherwise typically intelligent children. The prevalence of DLD is ~ 7-8% or 2% if severe forms are considered. This study aims to investigate a homogeneous cohort of DLD patients, excluding cases of ASD, ID or CAS, using multiple genomic approaches to better define the molecular basis of the disorder.

METHODS

Fifteen families, including 27 children with severe DLD, were enrolled. The majority of cases (n = 24) were included in multiplex families while three cases were sporadic. This resulted in a cohort of 59 individuals for whom chromosomal microarray analysis and exome or genome sequencing were performed.

RESULTS

We identified copy number variants (CNVs) predisposing to neurodevelopmental disorders with incomplete penetrance and variable expressivity in two families. These CNVs (i.e., 15q13.3 deletion and proximal 16p11.2 duplication) are interpreted as pathogenic. In one sporadic case, a de novo pathogenic variant in the ZNF292 gene, known to be associated with ID, was detected, broadening the spectrum of this syndrome.

LIMITATIONS

The strict diagnostic criteria applied by our multidisciplinary team, including speech-language physicians, neuropsychologists, and paediatric neurologists, resulted in a relatively small sample size, which limit the strength of our findings.

CONCLUSION

These findings highlight a common genetic architecture between DLD, ASD and ID, and underline the need for further investigation into overlapping neurodevelopmental pathways.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT06660108.

Role of sperm DNA damage in creating de-novo mutations in human offspring: the 'post-meiotic oocyte collusion' hypothesis

Spermatogonial stem cells exhibit a low level of spontaneous mutation that is heavily impacted by paternal age via mechanisms that appear to involve the aberrant repair of DNA damage. This background de-novo mutation frequency can be increased 1000-fold by mutations affecting a key signal transduction pathway that confers upon its descendants a selective advantage, leading to clonal expansion and nests of mutant germ cells in the testes of ageing males. This 'selfish selection' model effectively explains the origin of several dominant developmental disorders, such as achondroplasia and Apert syndrome, but cannot be generalized to account for the majority of de-novo mutations where no selective advantage is apparent. In this article, an additional germline mutation pathway is proposed that recognizes the unique susceptibility of spermatozoa to DNA damage and the importance of the oocyte in repairing these lesions prior to the S phase of the first mitotic division. Any deficiency or inaccuracy on the part of the oocyte in effecting this repair process has the potential to fix paternal DNA damage as a de-novo mutation in the embryo. Such a mechanism supports emerging data indicating that assisted conception procedures may enhance the mutational load carried by ART offspring.

Chromosome 15q BP4-BP5 Deletion in a Girl with Nocturnal Frontal Lobe Epilepsy, Migraine, Circumscribed Hypertrichosis, and Language Impairment

The 15q13.3 microdeletion (microdel15q13.3) syndrome (OMIM 612001) has been reported in healthy subjects as well as in individuals with a wide spectrum of clinical manifestations ranging from mild to severe neurological disorders, including developmental delay/intellectual disability, autism spectrum disorder, schizophrenia, epilepsy, behavioral problems and speech dysfunction. This study explored the link between this genomic rearrangement and nocturnal frontal lobe epilepsy (NFLE), which could improve the clinical interpretation. A clinical and genomic investigation was carried out on an 8-year-girl with a de novo deletion flanking the breakpoints (BPs) 4 and 5 of 15q13.3 detected by array comparative genomic hybridization analysis, affected by NFLE, migraine with aura, minor facial features, mild cognitive and language impairment, and circumscribed hypertrichosis. Literature survey of clinical studies was included. Nine years follow-up have displayed a benign course of the epileptic disorder with a progressive reduction and disappearance of the epileptic seizures, mild improvement of cognitive and language skills, partial cutaneous hypertrichosis regression, but stable ongoing of migraine episodes. A likely relationship between the BP4–BP5 deletion and NFLE with other symptoms presented by the girl is discussed together with a review of the literature on phenotypic features in microdel15q13.3.

Chromosome 15q BP3 to BP5 deletion is a likely locus for speech delay and language impairment: Report on a four-member family and an unrelated boy

BACKGROUND

Deletions in chromosome 15q13 have been reported both in healthy people and individuals with a wide range of behavioral and neuropsychiatric disturbances. Six main breakpoint (BP) subregions (BP1-BP6) are mapped to the 15q13 region and three further embedded BP regions (BP3-BP5). The deletion at BP4-BP5 is the rearrangement most frequently observed compared to other known deletions in BP3-BP5 and BP3-BP4 regions. Deletions of each of these three regions have previously been implicated in a variable range of clinical phenotypes, including minor dysmorphism, developmental delay/intellectual disability, epilepsy, autism spectrum disorders, behavioral disturbances, and speech disorders. Of note, no overt clinical difference among each group of BP region deletions has been recorded so far.

METHODS

We report on a four-member family plus an additional unrelated boy affected by a BP3-BP5 deletion that presented with typical clinical signs including speech delay and language impairment. A review of the clinical features associated with the three main groups of BP regions (BP4-BP5, BP3-BP5, and BP3-BP4) deletions is reported.

RESULTS

Array-CGH analysis revealed in the mother (case 1) and in her three children (cases 2, 3, and 4), as well as in the unrelated boy (case 5), the following rearrangement: arr (hg19) 15q13.1-q13.3 (29.213.402-32.510.863) x1.

CONCLUSION

This report, along with other recent observations, suggests the hypothesis that the BP region comprised between BP3 and BP5 in chromosome 15q13 is involved in several brain human dysfunctions, including impairment of the language development and, its deletion, may be directly or indirectly responsible for the speech delay and language deficit in the affected individuals.