NADD Bulletin Volume III Number 3 Article 2

Complete listing

Differential Diagnosis of Autism: The Importance of Medical Evaluation to Genetic Counseling

Carlos Eduardo Steiner, MD, MSc; Marilisa Mantovani Guerreiro, MD, PhD; Antonia Paula Marques-de-Faria, MD, PhD


Infantile autism, or simple autism, is a neuropsychological developmental disorder, the most commonly occurring pervasive developmental disorders. It is clinically characterized by abnormalities in three main areas: social interaction, language and communication, and interests and activities. Symptoms of these abnormalities must be present before the age of three, although the development during the first year may be relatively normal in many cases. Additional findings are mental retardation in 75% of the cases and epilepsy in 30%, as well as hyperactivity and other neurological signs. The clinical picture is quite variable among affected individuals. Even in the same person the symptoms may modify with growth (American Psychiatric Association, 1994; World Health Orgnanization, 1994). About 10% of cases of autism are due to or associated with specific etiologies such as congenital rubella, chromosomal abnormalities, or single gene disorders (Fommbonne, du Mazaubrun, Cans, & Grandjean, 1997; Skjedal, Sponheim, Ganes, Jellum, & Bakke, 1998).

There are no specific laboratory findings in autism, so several diagnostic scales were created on the basis of the clinical aspects, in order to define its diagnosis. The most useful are the criteria listed in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) from the American Psychiatric Association (1994), and the criteria of the International Classification of Diseases and Health Problems (ICD) (1994).

Besides the other pervasive developmental disorders, many other related conditions must be considered in the differential diagnosis of autism (see Table 1), and some of them are discussed in this paper. Although the final diagnosis may produce no significant difference in the treatment of the individual, the recognition of a specific cause may be importany concerning some matters, especially the genetic counseling of their relatives.

Chromosomal Disorders

Since the 70’s many chromosomal abnormalities have been identified in individuals with autism. The main purpose of these studies was to determine a chromosomal region that could contain gene(s) involved in the etiology of autism. However, this methodology failed to describe a specific etiology, since various kinds of abnormalities have been described in different regions of almost all chromosomes in individuals with autism. In fact, only a few of these seem significant enough to deserve mention.

Besides that, probably many of these people felt to have autism and represent cases of individuals with a chromosomal abnormality causing mental retardation (usually severe or profound), in whom there is language delay, poor social interaction and stereotyped movements, resulting in autistic features but not autism in itself.

Concerning chromosomal abnormalities in general, trisomy 21 or Down syndrome is the most common, occurring with a frequency of 1 in 770 living births, and characterized by a well known clinical picture (Jones, 1997). Most of these individuals demonstrate a pleasant personality that contrasts with the social impairment seen in autism. In spite of this, about 10% of patients with Down syndrome exhibit autistic behavior (Howlin, Wing, & Gould, 1995) and trisomy 21 can be detected in almost 2% of individuals thought to be autistic (Skjedal et al., 1998).

In reference to other chromosomal disorders, particular attention should be given to the proximal long arm of chromosome 15. There are several descriptions of autistic individuals showing abnormalities on this region, including the criptical region for Prader-Willi and Angelman syndromes (Schroer et al., 1998). A frequency of 1% to 3% of abnormalities in this chromosome is found in individuals with autism, as compared to only 0.025% in newborns from general population (Bundey, Hardy, Vickers, Kilpatrick, & Corbett, 1994). It is also suggested that maternal origin of the abnormal chromosomes 15 in autistic patients is more frequent (Schroer et al., 1998).

Monogenic and Other Genetic Disorders

Besides the chromosomal disorders, several conditions with genetic etiologies have been found in association with autism (Gilberg, 1993). Most of them represent anecdotal reports indicating a probable casual relationship. Others deserve mention due to a more consistent association, such as fragile X syndrome, tuberous sclerosis, neurofibromatosis type I, and hypomelanosis of Ito.

Fragile X syndrome is the most frequent cause of inherited mental retardation, with some studies indicating an incidence of 6% of all mentally retarded males and 2% of females with mild mental impairment (Warren & Ashley, 1995). Although its name refers to the X chromosome, and its diagnosis can be made by special chromosomal analysis techniques, fragile X is not a classical chromosomal condition, but a genetic disorder that follows an X-linked mode of inheritance, caused by the FMR-1 gene. It is clinically characterized by mental retardation, usually moderate to severe in males and mild to moderate in 1/3 of carrier females. Other features are long face, prominent jaw, large ears, macroorchidism (large testicles), and connective tissue anomalies. These findings are variable among affected males, being more evident with age. In females, the phenotype is usually milder. Behavioral and emotional abnormalities are also described, including repetitive motor behaviors (hand-biting and hand-flapping), repetitive speech patterns (echolalia, dysfunctional verbal communication), impaired socialization, perseveration, and gaze aversion (Kaufmann & Reiss, 1999). Since the detection of the fragile X chromosome in autistic individuals, several reports have mentioned high prevalences of fragile X syndrome in samples of people with autism, varying from 5% to 16% (Gillberg, 1988). For this reason, cytogenetic or molecular tests for the diagnosis of the fragile X syndrome have been included in the investigation of individuals with autism.

Tuberous sclerosis is an autosomal dominant disorder characterized by hamartomatous growth in multiple organs. Clinical findings are variable among affected individuals and include hypopigmented skin macules, facial angiofibromas (previously incorrectly described as adenoma sebaceum), seizures, and mental retardation. Over 50% of patients with this condition present with autistic behavior (Gillberg, Gillberg, & Ahlsen, 1994), and about 3% (Smalley, Tanguay, Smith, & Gutierrez, 1992) to 9% (Gillberg et al., 1994) of all cases of autism are estimated to be due to tuberous sclerosis.

Neurofibromatosis type I is another disorder with autosomal dominant inheritance whose major manifestations include six or more café-au-lait spots, neurofibromas and Lisch nodules. About 8% to 11% of people with this disorder present with mild mental retardation, learning disabilities, visuo-spatial deficits and/or behavioral problems (Legius, Descheemaeker, Fryns, & Van den Berghe, 1994). Some cases of neurofibromatosis are also suggested to be associated with autism (Gillberg, 1988). A prevalence of 0.6% of children with neurofibromatosis was found in an French survey of people with autism (Skjedal et al., 1998).

The condition designated as hypomelanosis of Ito is characterized by abnormal skin pigmentation, most frequently asymmetric areas of hypo- or hyperpigmentation following the lines of Blaschko, mental retardation, seizures, and/or other congenital abnormalities (Jones, 1997). It is suggested that about 10% of patients with this signs present autistic-like behavior (Pascual-Castroviejo et al., 1998), and that 0.5% of autistic individuals have hypomelanosis of Ito (Akefeldt & Gillberg, 1991). Although traditionally considered a syndrome, hypomelanosis of Ito seems now to represent a symptom complex associated with chromosomal or genetic mosaicism (Van Steensel & Steijlen, 1998). In light of this, individuals with these features should be submitted to a careful evaluation which includes cytogenetic analysis in fibroblasts.

Phenylketonuria is a well-known autosomal recessive disorder of phenylalanine metabolism. Untreated phenylketonuria was also reported among people with autism (Gillberg, 1988), but its frequency has been significantly reduced in developed countries since the introduction of early diagnosis and treatment.

Finally, metachromatic leukodistrophy, adrenoleukodistrophy, and GM1 gangliosidosis are examples of neurodegenerative diseases that should be included in the differential diagnosis of autism. These disorders are generally characterized by a period of normal development followed by progressive neuromotor and cognitive involution, resulting in social and communicative isolation. The diagnosis is usually facilitated by a distinct clinical picture and known biochemical basis.

Atypical Autism (Pervasive Developmental Disorder Not Otherwise Specified)

The diagnosis of atypical autism is considered when the patient does not fulfill all the required diagnostic criteria for autism, or the onset is after the age of three. It probably does not represent a distinct nosologic entity, and in general it occurs in association with mental retardation, usually severe (World Health Organization, 1994). Gillberg (1993) emphasized that the diagnosis of autism can be made in the presence of almost any other disorder or handicap. When the etiology of the mental retardation is clear, as prenatal rubella infection, chromosomal abnormalities or a well-known genetic condition, autism should be considered secondary to the disorder that caused the mental retardation.

The reasons why mental retardation is so often associated with autism still remain unclear, but probably the brain damage, in the majority of cases, is extensive enough to limit several cognitive processes (Sigman, Arbelle, & Dissanayake, 1995). In fact, abnormal patterns of neural organization and dendritic branching have been identified in necroscopic researches involving autism, Rett syndrome, Down syndrome, fragile X syndrome, and Angelman syndrome, suggesting a common pathogenetic process in these entities that could explain the overlapping of symptoms among them (Volpe, 1995).

The most difficult differential diagnosis of autism probably arises at the two extremes of clinical picture. At one end, the overlapping of mental retardation with autistic signs is obvious, especially absence of speech, body-rocking, hand flapping or self-injurious behavior, present in 50% of children with severe mental retardation (Ciaranello & Ciaranello, 1985; Ehlers & Gillberg, 1993). At the other end, it is hard to assure that a shy child with poor interpersonal relationship or language delay has really autism or just a variation of personality (Simonoff & Rutter, 1996).

Scandinavian authors use the therm “borderline childhood psychosis” to describe those individuals that demonstrate a greater sense of reality and a less hampered development of personality. In general, these children show poor relationship to other children of the same age, with an odd and bizarre behavior, often with restricted interests. They also prefer solitary activities and have few close friends. On the other hand, abnormalities of language or stereotyped movements are rare in this disorder (Mouridsen, Rich, & Isager, 1993).

Asperger Syndrome

Asperger syndrome is characterized by a deviant pattern of development in the same areas as seen in autism (American Psychiatric Association, 1994; World Health Organization, 1994), but few differences have been used to separate individuals with this condition from those considered to have the so- called typical autism. It is not clear whether or not Asperger syndrome is a condition distinct from autism. As in the latter, it is also more frequent in males than in females, with the same sex ratio, i.e., about 4:1 (Ehlers & Gillberg, 1993). However, Asperger syndrome usually includes no cognitive or psychomotor development delay. Deficit in social and emotional interaction, although present, seems to be less severe than in autistic individuals. On the other hand, clumsiness is more frequent in Asperger syndrome (Szatmari, Archer, Fisman, Streiner, & Wilson, 1995; Eisenmajer et al., 1996). Prognosis concerning independence and professional skills is usually better than in autism, but people with Asperger syndrome occasionally can demonstrate psychotic episodes in early adult life (Wing, 1981). Another difference is a larger familial aggregation, around 17% of cases with Asperger syndrome as compared to 2-3% in autism (Ciaranello & Ciaranello, 1985). Mild features of Asperger syndrome in the first-degree relatives of the individuals with this diagnosis are not uncommon (Gillberg, 1988).

Gillberg (1989) suggested that the differences between Asperger syndrome and “typical” autism represent variations in a spectrum of clinical features of a same neurobiological deficit, with a milder impairment in the former. According to this author, Asperger syndrome seems to be a more appropriate diagnosis for some individuals and autism for others, but the use of one or another does not mean that Asperger syndrome exists as an independent entity separated from autism.

Childhood Disintegrative Disorder

Childhood disintegrative disorder, also known as Heller psychosis or Heller syndrome, is a rare condition that occurs in both sexes (Burd, Fisher, & Kerbeshian, 1989), but occurring more common among males (American Psychiatric Association, 1994). This diagnosis should be considered when a child whose development was entirely normal for months or years, loses the previously acquired skills and exhibits behavioral changes. Loss of interest in the environment, stereotyped movements, and deficiency in the social interaction and communication are described. The onset is usually between two and four years of life, but later onset has been reported in a few individuals. The neurologic regression can be insidious or abrupt, and progresses for many years into a state of severe mental retardation. Thus, the prognosis tends to be worse than in autism (American Psychiatric Association, 1994; Burd et al., 1989).

Other neurological signs can occur, such as EEG abnormalities, epilepsy, hyperactivity, attention disorder, obsessive behavior, hypoacusia, and tendency to isolation (Hill & Rosenbloom, 1986). Some individuals have preservation of motor skills in spite of cognitive impairment (Evan-Jones & Rosenbloom, 1978). Again, it is still unclear if this really represents a nosological distinct entity or just a variation of autism.

Rett Syndrome

Rett syndrome is a disorder that affects only females, with a frequency about 1:10,000 to 15,000 living women. Rett syndrome is currently considered a developmental disorder rather than a neurodegenerative disease (Olsson & Rett, 1987; Schwartzman, 1991).

Individuals with Rett syndrome have an apparently normal development until the age of six to eighteen months. Then, the neurologic acquisitions stop and later regress. There is simultaneous deceleration of ponderal and head growth, with acquired microcephaly. Typical aspects include loss of meaningful hand movements and appearance of stereotyped midline gestures resembling hand wringing, twisting or washing. Other signs include hyperpnea, epilepsy, and tooth grinding (Schwartzman, 1991).

Important motor and cognitive impairment develop between two to four years. Other characteristics are social isolation, absence of language (or other non-verbal communication), and behavioral changes like cry-crisis, and at least at this age the clinical picture nearly resembles autism. Later on, trunk ataxia and apraxia begin, motor skills tend to be lost, and there is progressive scoliosis, as well as trophic changes. The final picture is severe mental retardation with quadriparesis (Schwartzman, 1991).

Comparing with autism, some differences may be noted. First of all, Rett syndrome occurs only in females, while autism has a strong male preponderance. People with Rett syndrome show a better performance in social interaction, spotting a familiar person, smiling or laughing when approached allowing a longer eye contact, accepting touch, and sometimes exhibiting hyperventilation. They rarely have self-injurious behavior; and the repertoire of stereotypic movements is usually restricted (hand wringing), without variation in form or speed, while autistic individuals can develop complex movements with the whole body, including shaking, walking, dancing and speaking. Besides, loss of meaningful hand movements is seen in Rett syndrome but not in autism. Finally, periods of akinesia and amimia are frequent in the former, but are quite uncommon in the latter (Olsson & Rett, 1987).

Rett syndrome is generally sporadic and the recurrence risk is lower than 1%.

Other Neuropsychiatric Disorders

Congenital deafness shares some features with autism, especially speech delay, failure to turn around when called, and apparent lack of interest in the environment (Rapin, 1991). On the other hand, generally there is no ritualistic or stereotyped behavior, and social interaction, although deficient in its quality, is present. Deafness may be part of other conditions with mental retardation, such as congenital rubella, but individuals with isolated deafness do not have mental impairment.

Selective mutism is a diagnosis applicable to children who speak only when they are alone or with their closest friends, and sometimes with their parents, but never in public situations, as in school or with strangers. It is associated with some impairment in language development and social interaction, but generally there is no stereotyped movements or restricted patterns of interests or abnormal behaviors (Simonoff & Rutter, 1996).

The syndrome of acquired aphasia with epilepsy, also known as Landau-Kleffner syndrome, is characterized by loss of receptive and expressive language in a child with previously normal development. Epilepsy or transient EEG abnormalities are common, as well as behavior problems. In contrast to autism, non-verbal functions remain intact and there are no stereotyped behaviors (Simonoff & Rutter, 1996).

Autism differs from schizophrenia by the age of onset (before three years), static evolution, and absence of hallucinations and delusions, while schizophrenia begins generally at adolescence or young adulthood, has a variable course with periods of worsening and/or remission. Schizophrenia is characterized by hallucinations, delusions and other signs of thought dysfunction (Rapin, 1991).

Tourette syndrome usually begins in middle childhood with facial tics (eye blinking or grimaces), and progressing to motor tics, sometimes as complex as stereotyped or purposeful movements. Vocal tics include grunts, words or phrases, coprolalia or echolalia. Other symptoms are hyperactivity, anxiety, depression, and self-injury, the last often resulting from involuntary movements. Individuals with Tourette syndrome also have problems with interpersonal interaction, and frequently experience social rejection. It is a chronic disorder, with a variable and fluctuating course which often worsens in adolescence. In spite of aspects which are similar to autism, affected individuals usually have normal intelligence (Simonoff & Rutter, 1996).

Attention deficit disorder with hyperactivity or hyperkinetic syndrome is characterized by a persistent pattern of overactivity, inattention, and impulsiveness, with onset before the age of seven years. It is accompanied by social impairment, immaturity, and learning difficulties, and has a male preponderance of 4 to 5:1. In contrast to people with autism, hyperkinetic individuals usually are verborreic (talk a lot), interrupting or intruding on other’s speech, and do not maintain the same activity for long. Symptoms of hyperactivity can occur in other diseases, as the fragile X syndrome, but “pure” hyperkinetic syndrome is a distinct neurologic disorder, with familial aggregation and a relatively poor prognosis, which means tendency to antisocial behavior, criminality or drug abuse in 25% of adults with this diagnosis (Simonoff & Rutter, 1996).

Final Considerations

The list of the conditions with neuropsychiatric manifestations considered in a differential diagnosis of autism is extensive (Table I). They must be considered in any individual presenting abnormalities in socialization, communication, and/or activities, independent of the level of intellectual functioning. Clinical evaluation of a suspected case of autism should involve a careful collection of information about behavior patterns, onset of problems, and evolution through childhood. Autism can also be secondary to many genetic conditions, especially chromosomal abnormalities, fragile X syndrome, and tuberous sclerosis.

The diagnosis among the different types of pervasive developmental disorders may lead to a more accurate prognosis for the individual. Diagnosing a specific genetic condition may not modify the treatment of this individual, but is of significant importance in the genetic counseling of their relatives. “Pure” or idiopathic autism most probably occurs as a multifactorial disorder, and has a recurrence risk of about 2-3% in first-degree relatives (Ciaranello & Ciaranello, 1985). Conditions such as phenylketonuria, metachromatic leukodistrophy, or GM1 gangliosidosis follow autosomal recessive mode of inheritance, with a recurrence risk of 25% for each new pregnancy, i.e., 10 times greater than idiopathic autism. In the Fragile X syndrome, in which the sisters, aunts and even cousins of an affected individual are under risk, the recurrence rates vary from 9% to almost 50%, depending on the carrier status in the genealogy. In tuberous sclerosis and neurofibromatosis, if one of the parents is also affected, the recurrence risk may be as high as 50%.

For this reason, besides neurologic or psychiatric evaluation, a careful dysmorphologic (including dermatologic) examination should be performed to search for suggestive signs of neurogenetic disorders. Besides, karyotype and the molecular study of the fragile X syndrome should be included in the etiological investigation of autism. All these will provide conditions to a specific diagnosis, which is essential to the genetic counseling.


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This work was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) of Brazil. Departamento de Genética Médica1 and Departamento de Neurologia2, Universidade Estadual de Campinas (UNICAMP), Campinas, SP, Brazil.

Correspondence should be sent to:

Carlos E. Steiner
Dep. Genética Médica – FCM – UNICAMP
C.P. 6111
CEP 13081-970 Campinas – SP Brazil