As prevalence of autism spectrum disorders (ASD) has increased to 1 in 59 children (Baio et al., 2018), clinicians concentrate on investigating relations among ASD phenotypes and disorders which share similarities with ASD (Cohen et al., 2005; Moss & Howlin, 2009; Rumsey et al., 2014). Clinicians may be less familiar with disorders that share symptomology and similarities (e.g., social communication deficits; restricted, repetitive behavior; problem behavior; and sleep problems: American Psychiatric Association, 2013) yet have different developmental and treatment trajectories. For example, mucopolysaccharidosis-IIIA (MPS-IIIA; Sanfilippo syndrome), a lysosomal storage disease, results in central nervous system (CNS) damage. This damage results in progressive physiological symptoms and regression of skills as children age, despite early skill and behavior development resembling ASD and responses to intervention (Rumsey et al., 2014; Wijburg, et al., 2013; Wolfenden, et al., 2017).The rarity of MPS-IIIA (1 in 100,000 children) explains clinicians’ lack of exposure to the disease and symptoms’ similarities to ASD (Fedele, 2015; Heron et al., 2010; Rumsey et al., 2014; Sorrentino & Fraldi, 2016; Wijburg et al., 2013; Wolfenden et al., 2017).

Clinicians who specialize in ASD may receive referrals to work with these children before an MPS-IIIA diagnosis. Non-medical clinicians may be the first professional families access. Although clinicians may suspect a difference, lack of exposure to MPS-IIIA may hinder identification. Failure in early identification of MPS-IIIA restricts medical research and treatment support for children with a limited lifespan. Since no cure or physiological treatments exist for the CNS degeneration in MPS-IIIA (Cleary & Wraith, 1993; Fedele, 2015; Sorrentino & Fraldi, 2016; Stapleton et al., 2019; Valstar et al., 2008), clinicians must learn the progression of MPS-IIIA to provide interdisciplinary and appropriate interventions to improve the quality of life for these children and families beyond just palliative care (Cleary & Wraith, 1993; Ghosh et al., 2017; Grant, 2021; Shapiro et al., 2016; Stapleton et al., 2019; Wijburg et al., 2013). This paper provides a guide to identifying MPS-IIIA and suggestions for applications of non-medical, existing interventions.

Symptoms and Progression: Discriminating MPS-IIIA from ASD

Physiological

From infancy, children with MPS-IIIA exhibit facial characteristics and medical conditions subtly differentiating them from other children with ASD (see Table 1). Physiological symptoms gradually worsen during young childhood. During pre-adolescence, children with MPS-IIIA experience significant physical regression and worsening comorbid medical conditions (Shapiro et al., 2018; Valstar et al., 2008; Wijburg et al., 2013; Wolfenden et al., 2017). Physical health and mobility diminish leading to early death (average 15 years old: range 8.5–29 years) often from physiological complications (Cleary & Wraith, 1993; Delgadillo et al., 2013; Heron et al., 2010; Malm & Mansson, 2010; Meyer et al., 2007; Valstar et al., 2008, 2010; van de Kamp et al., 1981; Wijburg et al., 2013).

Table 1 Discrimination and similarities to ASD for MPS-IIIA symptoms and progressions across ages and domains

Cognitive, Communication, and Social

In infancy, MPS-IIIA may be difficult for clinicians to detect (Bax & Colville, 1995; Ghosh et al., 2017; Meyer et al., 2007; Valstar et al., 2010) with one-fourth of infants developing typical social, communication, and cognitive skills (Meyer et al., 2007; Nidiffer & Kelly, 1983). As a toddler (e.g., 1–4 years old), they exhibit more distinct differences, resembling the social, communication, and cognitive development of children with ASD, such as missed developmental milestones, delayed speech, echolalia, lack of eye contact, and fewer social interactions (Buhrman et al., 2014; Cleary & Wraith, 1993; Cohen et al., 2005; Heron et al., 2010; Malm & Mansson, 2010; Nidiffer & Kelly, 1983; Rumsey et al., 2014; Shapiro et al., 2015; van de Kamp et al., 1981; Wijburg et al., 2013; Wolfenden et al., 2017). See Table 1 for symptoms and progressions.

For those with speech, communication regression occurs as early as 2 to 4 years old (Bax & Colville, 1995; Buhrman et al., 2014; Meyer et al., 2007; Wijburg et al., 2013), which may resemble regressive ASD versus early onset autism (Ozonoff, et al., 2005). As in ASD, communication difficulties co-occur with social skill problems, such as delayed communication co-occurring with lack of gesture use, play skills, and joint attention (Cohen et al., 2005; Nidiffer & Kelly, 1983; Rumsey et al., 2014; Wolfenden et al., 2017). By 3 to 4 years old, social communication skills so highly resemble ASD that toddlers with MPS-IIIA often receive an ASD diagnosis often without the accompanying MPS-IIIA diagnosis (Rumsey et al., 2014; Wijburg et al., 2013; Wolfenden et al., 2017).

Impaired cognitive ability and increased communication deficits resembling ASD become more obvious as the child ages (Buhrman et al., 2014; Cleary & Wraith, 1993; Cohen et al., 2005; Delgadillo et al., 2013; Heron et al., 2010; Malm & Mansson, 2010; Meyer et al., 2007; Nidiffer & Kelly, 1983; Rumsey et al., 2014; Schreck et al., 2018; Shapiro et al., 2016; Valstar et al., 2010; van de Kamp et al., 1981; Wijburg et al., 2013; Wolfenden et al., 2017). Children continue to experience delays and exhibit symptoms similar to ASD (e.g., delayed speech, loss of eye contact, restricted facial expressions) until experiencing a regression. Young children with MPS-IIIA (e.g., 4–10 years old) with rapid progression experience severe regression resembling dementia such as memory loss, diagnoses of intellectual disabilities, loss of understanding and use of words, and reduced interactions with others (Buhrman et al., 2014; Delgadillo et al., 2013; Malm & Mansson, 2010; Meyer et al., 2007; Nidiffer & Kelly, 1983; Schreck et al., 2018; Shapiro et al., 2016; Shapiro & Eisengart, 2021; Sorrentino & Fraldi, 2016; Truxal et al., 2016; Valstar et al., 2008; van de Kamp et al., 1981; Wijburg et al., 2013). Those experiencing slower regression eventually experience a similar end result loss of skills (Shapiro et al., 2016). Once speech regression begins, loss of words occurs quickly with total loss of speech and cognitive abilities typically occurring by 8 years old (Buhrman et al., 2014; Delgadillo et al., 2013; Schreck et al., 2018). Regression of receptive language occurs more gradually than loss of expressive speech (Buhrman et al., 2014). This regression and loss of skills also occur for social skills (Buhrman et al., 2014; Delgadillo et al., 2013; Nidiffer & Kelly, 1983; Schreck et al., 2018; Shapiro et al., 2016; Sorrentino & Fraldi, 2016; Valstar et al., 2011).

The skill regression for children with MPS-IIIA can result in diagnostic differentiation by 4 years old for clinicians aware of MPS-IIIA (Colville & Bax, 1996; Meyer et al., 2007). Even for clinicians less familiar with MPS-IIIA, the continued regression of skills differentiates pre-adolescents with MPS-IIIA. By pre-adolescence, ability to communicate typically disappears (Meyer et al., 2007; Nidiffer & Kelly, 1983; Shapiro et al., 2018; Valstar, et al., 2018). Additionally, adolescents lose the social skills that began to deteriorate during young childhood. By 10 years old, pre-adolescents to adolescents (e.g., 10 + years old) may completely lose the ability to socially relate to others (Heron et al., 2010).

Motor and Related Skills

Infants and toddlers have gross and fine motor skills sometimes occurring within normal developmental time periods and developing into social and adaptive use of motor skills (Bax & Colville, 1995; Buhrman et al., 2014; Cleary & Wraith, 1993; Delgadillo et al., 2013; Heron et al., 2010; Malm & Mansson, 2010; Nidiffer & Kelly, 1983; Schreck et al., 2018; Shapiro et al., 2015; van De Kamp et al., 1981. In young childhood, motor difficulties resemble those of children with ASD (Table 1 provides symptoms and progressions). However, unlike children with just an ASD diagnosis, children with MPS-IIIA experience significant motor and adaptive behavior regression from 4 to 10 years old (Buhrman et al., 2014; Shapiro et al., 2016), losing toileting and feeding skills (Cleary & Wraith, 1993; Niddifer & Kelly, 1983), and experiencing movement or balance problems and regression of walking (Buhrman et al., 2014; Cleary & Wraith, 1993; Delgadillo et al., 2013; Mariotti et al., 2003; Schreck et al., 2018; Shapiro et al., 2018). By adolescence, physiological symptoms worsen effecting motor skills (Cleary & Wraith, 1993; Meyer et al., 2007; Valstar et al., 2008; Wijburg et al., 2013). Most motor skills regress or disappear by approximately 12 years—adolescence (Meyer et al., 2007) with increased falls and total loss of walking, difficulty or inability to swallow, and complete immobility and unresponsiveness until death (Buhrman et al., 2014; Cleary & Wraith, 1993; Fedele, 2015; Heron et al., 2010; Malm & Mansson, 2010; Mariotti et al., 2003; Schreck et al., 2018; Shapiro et al., 2018; Valstar et al., 2008; Wijburg et al., 2013).

Behavior Problems

Toddlers and young children with MPS-IIIA exhibit behavior problems similar to those with ASD, such as sleep problems, problem behaviors, restricted interests/stereotypy, attention deficit hyperactivity disorder, and anxiety (Bax & Colville, 1995; Buhrman et al., 2014; Cleary & Wraith, 1993; Cohen et al., 2005; Colville, et al., 1996; Cross & Hare, 2013; Delgadillo et al., 2013; Fraser, et al., 2005; Fraser, et al., 2002; Heron et al., 2010; Hoffman et al., 2020; Mahon et al., 2014; Mariotti et al., 2003; Meyer et al., 2007; Nidiffer & Kelly, 1983; Rumsey et al., 2014; Schreck et al., 2018; Shapiro et al., 2015; Valstar et al., 2008; van de Kamp et al., 1981; Wijburg et al., 2013; Wolfenden et al., 2017). These diverse behaviors begin and worsen from 3 to 5 years old and increase into young childhood (Bax & Colville, 1995; Buhrman et al., 2014; Cleary & Wraith, 1993; Colville et al., 1996; Fraser et al., 2005; Ghosh et al., 2017; Heron et al., 2010; Malcolm, et al., 2012; Mariotti et al., 2003; Meyer et al., 2007; Nidiffer & Kelly, 1983; Rumsey et al., 2014; Schreck et al., 2018; Shapiro et al., 2015, 2018; Truxal et al., 2016; Valstar et al., 2010; Wijburg et al., 2013). In young childhood, they also may develop other behaviors resulting in an ASD diagnosis, such as self-injurious behavior, lethargy, disrobing, perseverative mouthing behavior, mood swings and crying, and separation anxiety (Bax & Colville, 1995; Buhrman et al., 2014; Cohen et al., 2005; Malcolm et al., 2012; Nidiffer & Kelly, 1983; Rumsey et al., 2014; Schreck et al., 2018; Shapiro et al., 2015; Valstar et al, 2010; Wolfenden et al., 2017; Wijburg et al., 2013.

By pre-adolescence/adolescence, behavioral symptoms differentiate them from their peers. Although sleep disturbances can remain problematic, other behaviors tend to decrease or disappear (Buhrman et al., 2014; Cleary & Wraith, 1993; Colville et al., 1996; Ghosh et al., 2017; Mariotti et al., 2003; Nidiffer & Kelly, 1983; Schreck et al., 2018; Valstar et al., 2008, 2010; Wijburg et al., 2013), possibly due to physiological progression of the disease impeding behavior problems (Buhrman et al., 2014; Cleary & Wraith, 1993; Wijburg et al., 2013). However, crying/mood swings may maintain, even in absence of any obvious signs of pain (Cleary & Wraith, 1993; Shapiro et al., 2018).

Interventions

Physiological

Physiological interventions for all ages of children with MPS-IIIA remain symptom and location-based, for example, seizure medication, ear tube implants, hearing aids, glasses, and physical therapy or splints for scoliosis, pain, and contractures (Buhrman et al., 2014; Cleary & Wraith, 1993; Meyer et al., 2007; Wijburg et al., 2013. No intervention exists for the physiological CNS regression or cause of MPS-IIIA (Buhrman et al., 2014; Fedele, 2015). CNS degeneration contributes to clinician’s differentiation of MPS-IIIA allowing for additional pharmacologic and nutritional symptom interventions to improve comfort and quality of life. However, the empirically supported evidence for the effectiveness of these interventions remains equivocal (Cleary & Wraith, 1993).

Social, Communication, Cognitive, Motor, and Adaptive

Although research supported behavioral interventions exist for instruction of social, communication, cognitive, motor, and adaptive skills for children with ASD (National Autism Center, 2009, 2015), only one report of teaching skills for a pre-adolescent with MPS-IIIA was located (Schreck et al., 2018). Schreck and colleagues (2018) used behavioral interventions to teach (a) use of an augmentative communication device for requesting (e.g., foods, people, activities) in multiple environments after verbal regression, (b) acquisition and maintenance of motor skills, (c) use of play skills, and (d) maintenance of adaptive behavior. Additionally, some researchers suggest that interventions and physical therapy commonly used in ASD instruction may result in partial success for teaching and maintaining mobility, toileting, hygiene, and feeding (Cleary & Wraith, 1993; Nidiffer & Kelly, 1983; Schreck et al., 2018). These recommendations suggest that children with MPS-IIIA can learn and maintain skills to improve quality of life; however, controlled research must be conducted to determine instructional methods. Until then, clinicians must generalize from effective interventions for children with ASD (National Autism Center, 2009, 2015; Rumsey et al., 2014).

Behavior Problems

Very few research studies provide clinical recommendations for reducing behavior problems specifically in this population. Recommendations remain mostly hypothetical or contradicting. For example, some research supports using pharmacological treatments, such as antipsychotics, melatonin, benzodiazepines, and seizure medications (Cleary & Wraith, 1993; Fraser et al., 2002, 2005; Guerrero, et al., 2006; Hoffman et al., 2020; Nidiffer & Kelly, 1983; Valstar et al., 2008) and contends the lack of effectiveness of behavioral interventions (Cleary & Wraith, 1993; Wijburg et al., 2013). Others suggest pharmacological treatments may be mostly entirely ineffective or requires significant precautions (Cleary & Wraith, 1993; Hoffman et al., 2020; Nidiffer & Kelly, 1983; Valstar et al., 2008; Wijburg et al, 2013), and behavioral treatments show promise (Colville et al., 1996; Escolar, et al., 2017; Fraser et al., 2002, 2005; Nidiffer & Kelly, 1983; Schreck et al., 2018; Valstar et al., 2008; Wijburg et al., 2013). No studies directly and empirically evaluate the effectiveness of pharmacological treatment or its interaction with behavioral interventions as recommended for Intellectual and Developmental Disability populations (IDD: Napolitano et al., 1999; Sprague & Werry, 1971). Two studies indicate the possible effectiveness of behavioral interventions (sleep problems, Colville et al. (1996); pica, hand mouthing, tantrums, Schreck et al. (2018)). Thus, clinicians’ intervention choices remain significantly limited to preliminary evidence. Until more research exists, professionals must choose interventions from effective interventions for children with ASD/IDD (National Autism Center, 2015; Rumsey et al., 2014) which include function-based treatments (e.g., attention, tangibles, automatic, escape/avoidance) that may be related to behavioral topography (Matson et al., 2011; Williams & McAdam, 2012).

Conclusion

Children with MPS-IIIA exhibit skill deficits and behavior problems initially resembling the symptomatic patterns of children with ASD, often leading to a diagnosis of ASD (Rumsey et al., 2014; Wolfenden et al., 2017). Due to their ASD diagnoses and the effectiveness of behavior interventions in ASD (National Autism Center, 2009, 2015), clinicians may receive referrals to provide behavioral interventions to alter environmental stimuli (e.g., changing antecedent conditions and assessing and treating behaviors according to functions). Although preliminary research suggests that these behavioral interventions may be effective (Colville et al., 1996; Schreck et al., 2018), children with MPS-IIIA’s response may differ from their peers with ASD who do not have the underlying physiological degeneration. For example, interventions may initially result in communication acquisition, but not maintenance. Further, a comprehensive and interdisciplinary (medical and behavioral) approach may be necessary to treat physiological symptoms (e.g., pain, seizures, and contractures) in conjunction with behavior (see Milnes and Piazza (2013) for example of this approach in another population). Without exposure to MPS-IIIA, clinicians may choose inappropriate learning objective goals (e.g., continuing verbal instruction in place of augmentative communication) or may struggle with providing appropriate treatment.

As no cure for MPS-IIIA exists and clinical intervention primarily concentrates on reducing physiological symptoms (Fedele, 2015; Sorrentino & Fraldi, 2016) or palliative care (Cleary & Wraith, 1993; Stapleton et al., 2019; Wijburg et al., 2013), clinicians must expand the research based on skill acquisition, skill maintenance, and behavior problem reduction. Additionally, clinicians should investigate the effects of early intervention on the effectiveness of treatments (Shapiro et al., 2016) which may allow clinicians to teach alternative or modified skills before skill and behavioral regression. Addressing skills and behavioral issues have been identified as pre-eminent in increased quality of life, continued interactions, and familial adjustment (Buhrman et al, 2014; Portera et al., 2020; Ghosh et al., 2017; Grant, 2021). Developing effective, individualized interventions for children with MPS-IIIA may lead to more positive and effective interactions with their families and peers and increased maintenance of independence. Until a cure can be found, clinicians must strive to maintain or increase the quality of these children’s and their families’ lives.