Autism spectrum disorder (ASD) is a group of conditions in which the person experiences significant difficulties in socialization, communication, and language (1). In addition, people with ASD exhibit unusual repetitive behaviors (2). Despite the lack of a clear mechanism, genetics have a significant role in the etiology of ASD; previous research studies conducted on families and twins have elucidated specific genetic causes for isolated cases, and a number of candidate genes and chromosomal regions have been indicated as relevant across multiple studies, including 2q, 7q, 15q, and 17q (3, 4). Genome-wide studies using genotyping microarrays, whole-exome sequencing, and whole-genome sequencing have identified a rapidly growing number of genes linked to ASD; furthermore, cumulative discoveries of de novo mutations have pointed the field in various directions, including the converging actions of ASD-associated mutations and progressive use of translational strategies (in animals and humans) to understand the outcomes of replicated ASD-associated mutations (5–7).

Calcium ions are involved in several human cellular processes including corticogenesis, transcription, and synaptogenesis and play a major role in the development of neurodevelopmental disorders (8). Since the calcium signaling pathway was recognized among the top three pathways involved in ASD, many discoveries of point mutations in the α1-subunit of L-type calcium channels (CaV1.2) and many other genes encoding voltage-gated calcium channel (VGCC) subunits, such as CACNA1B-F encoding pore-forming subunits, CACNB1 and CACNB2 encoding auxiliary β-subunits, and CACNA2D3 and CACNA2D4 for auxiliary α2-δ-subunits have been associated with ASD (9).

Voltage-gated calcium channels (VGCCs) are transmembrane proteins that are activated by depolarization, triggering Ca²⁺ influx into neurons and other excitable cells, which are composed of a pore-forming α1 subunit and auxiliary α2δ and β subunits (10). Until now, 10-mammalian VGCCs have been identified, and based on their activation threshold. CaVs are classified as high or low voltage activated (HVA and LVA) (11). One of the three main families of the LVA subgroup is the L-type Ca²⁺ channels (LTCCs; Cav1), which consists of four subtypes: Ca_v1.1, Ca_v1.2, Ca_v1.3, and Ca_v1.4 (12). The main functions of Ca_v1.1 include the excitation–contraction coupling in skeletal muscles and the regulation of transcription in these muscles. The main functions of Ca_v1.2 include excitation–contraction coupling in cardiac and smooth muscles, hormone secretion, and neurotransmitter release. The functions of Ca_v1.3 are similar to those of Ca_v1.2, with the addition of cardiac pace-making and auditory transduction. The Ca_v1.4 plays a role in visual transduction. Ca_v1.2 and Ca_v1.3 are expressed in the most electrically excitable cells, including various areas of the brain (13, 14) (Table 1). The variants in CACNA1C, CACNA1D, CACNA1F, and CACNB2 cause gain-of-function by preventing voltage-dependent inactivation of their subunits (Cav1.2, Cav1.3, Cav1.4, and Cavβ2), leading to an excessive influx of Ca²⁺, alteration in kinetics (activation and inactivation), and dominant-negative effects of truncated forms of alpha1 subunits (8). Variants located in CACNA1A and CACNA1H are the cause of the loss of function in encoded subunits (Cav2.1 and Cav3.2), resulting in decreased channel activity (16).

The subject of the case report is a 9-year-old girl who was born at full term via normal spontaneous vaginal delivery to a healthy mother following an uneventful pregnancy. The neonatal history was unremarkable. Her mother started to seek medical advice at the age of 4 years as the child exhibited speech and language delay with challenging behaviors. These challenging behaviors took the form of aggressiveness, self-injurious behaviors, stereotyped and repetitive motor mannerisms with hand flapping and body rocking, lack of sleep, and attention-deficit hyperactivity-like disorders.

Previous studies have linked germline CACNA1D gene mutations in extended clinical phenotypes with certain neuropsychiatric and neurodevelopmental disorders, childhood epilepsies, and ASD (21). Heterozygous missense gain-of-function mutations are associated with neuropsychiatric disorders, developmental delay, and ASD. Gain-of-function variants in the CACNA1D gene have been identified as somatic mutations in aldosterone-producing adenoma (22). These findings support the idea that homozygous loss-of-function mutations, such as frameshift, premature stop codon, and splice-donor defect, result in a loss of channel function that causes deafness, bradycardia, and sinoatrial node arrhythmia (human sinoatrial node dysfunction and deafness syndrome, OMIM 614896) (15).

In this case report, we describe a case that is not related to the previous cases with the S672L variant in CACNA1D and with similar phenotypes of ASD (23); however, the patient in this case is reported to have inherited the variant from her father, whose clinical presentation mainly included ID, psychiatric illness, and seizures, which developed near the end of his life, but no autistic features. Moreover, her sister is known to have ID and a psychiatric disorder and exhibits aggressiveness and impulsive behaviors; however, she is not known to have autistic features either. None of the five cases with S672L has hypertension, hyperaldosteronism, or evidence of hyperinsulinemia (Table 2).

We searched all the studies related to the CACNA1D gene that were published in PubMed between 2000 and 2022; detailed information from these articles is organized in Tables 2, 3. From the three cases described in this case study and previous clinical reports of 11 individuals, we attempted to delineate the spectrum of clinical phenotypes of missense gain-of-function mutations in the CACNA1D gene (15, 24–31).

Most (85%) patients presented with intellectual impairment or disability (only three cases did not report ID, two of which did not detail any clinical phenotype). Over half (55%) of the patients presented with ASD, and it was the presenting clinical phenotype of the subject of this case study (case 12); however, the subject’s father and sister (case 13 and case 14) were not clinically diagnosed to have ASD, which could be related to their late clinical presentation or misdiagnosis of psychiatric illnesses instead of ASD. Aggressiveness and self-injurious behaviors were detected in all cases with the S672L variant except one (case 14). In addition, these phenotypes were detected in two individuals with different variants (A749T and L271H; case 10 and case 12, respectively), and this clinical phenotype accounts for approximately 40% of the reported cases. Endocrine symptoms were not consistent and were only being observed in a third of the cases. They were the first clinical presentation that required immediate therapeutic intervention in patients with primary aldosteronism, seizures, and neurologic abnormalities and in the individuals affected by congenital hyperinsulinemic hypoglycemia (G403D) and (L271H) (24, 25, 30). Their absence does not rule out a CACNA1D channelopathy, and their presence cannot be predicted from the variant gating change. Furthermore, they should be monitored for symptoms of primary aldosteronism (case 11) and altered glucose homeostasis even if not present in the peri- and post-natal periods. No clear dysmorphic facial features were reported, and they are not consistent clinical features in the CACNA1D gene mutation as they are found in only 28% of the reported cases.

As discussed above, Cav1.3 L-type channels are also present in other tissues. Although the homozygous loss of Cav1.3 function results in congenital deafness and sinoatrial node dysfunction, it is currently unclear whether the heterozygous gain-of-function gating changes of the reported variants result in clinically relevant hearing-related symptoms or directly cause the cardiac abnormalities observed in some cases (15) (Table 2).

Hofer et al. functionally characterized the potential changes in the S652L variant. This mutation significantly shifted the voltage dependence of activation and steady-state inactivation to more negative potentials (~13–17 mV), further increasing window currents at subthreshold voltages. Moreover, it slowed tail currents and increased Ca²⁺ levels during action potential-like stimulations, which is characteristic of gain-of-function changes (20). An understanding of the effects of coding mutations on protein function and interaction can guide the treatment and management strategies. The heterozygous CACNA1D variants alter gating changes that increase Cav1.3 channel activity. Thus, the inhibition of Cav1.3 channel activity with drugs appears to be a potential treatment option in the affected individuals. The S672L mutation increased the sensitivity of Cav1.3 to inhibition by the dihydropyridine LTCC blocker isradipine by 3- to 4-fold (20). Although LTCC blockers may normalize the mutation-induced increase in channel function after diagnosis, the mutation may have already caused permanent developmental deficiencies that are resistant to drug treatment, and none of the reported cases showed a conclusive effect of this treatment on neurological or behavioral disorders (24). Therefore, the clinical effect of LTCC blockers needs to be tested in small clinical trials involving affected individuals.

This case report and all previous clinical reports shed light on the link between the CACNA1D gene mutation and neurodevelopmental disorders. A broad spectrum of clinical phenotypes was observed, ranging from ASD, with or without seizures and psychiatric disorders, to severe global developmental delay. The missense gain-of-function mutation in CACNA1D is inherited in autosomal dominant mode with complete penetrance, as shown in this case study. The minority of the reported cases have endocrinological disorders, such as hyperaldosteronism and hyperinsulinism, but they should be monitored as they might manifest later in life.

The datasets presented in this article are not readily available because of ethical and privacy restrictions. Requests to access the datasets should be directed to the corresponding author.

Ethical review and approval was not required for the study on human participants in accordance with the local legislation and institutional requirements. Written informed consent to participate in this study was provided by the participants’ legal guardian/next of kin. Written informed consent was obtained from the individual(s), and minor(s)’ legal guardian/next of kin, for the publication of any potentially identifiable images or data included in this article.

AA participated in writing the background with significance, case presentations, discussion, conclusion, references, designating tables, and read and approved the final manuscript. MaA, MoA, AB, and NA helped draft the manuscript, read and agree on the final manuscript, and formatted the manuscript according to the journal’s guidelines. FA supervised the overall research, preparing the manuscript reading, and approving the final manuscript. All authors contributed to the article and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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