Typical and Atypical Development

Child Development Concepts

Child development is a continuous process of acquiring new and advanced skills. This development depends on maturation of the nervous system. Although typical child development follows a relatively consistent sequence, it is not linear. Instead, there are spurts and lags. For example, motor development in the first year of life proceeds relatively rapidly. Babies typically mature from being completely immobile to walking in just over 12 months, but then motor development progresses less dramatically during the second year of life. Conversely, language development in the first year of life occurs slowly, but there is an explosion of language acquisition between a child’s first and second birthdays.

On average, most children achieve each developmental milestone within a defined and narrow age range (Table 7.1). Usually physicians learn the average age for acquiring specific skills. However, since each developmental skill can be acquired within an age range, it is much more useful clinically to know when a child’s development falls outside this range. These so-called red flags are important because they can be used to identify when a child has developmental delay for specific skills. For example, although the average age of walking is approximately 13 months, a child may walk as late as 17 months and still be within the typical developmental range. In this example, the red flag for independent walking is 18 months, and a child who is not walking by 18 months of age is delayed.

Table 7.1 Normal Developmental Milestones by Age (50th-75th Percentile)

Global Developmental Delay

Developmental History

Child development is classically divided into five interdependent domains or streams: gross motor, fine motor and problem-solving, receptive language, expressive language, and socialization/adaptive. The approach to a child with possible developmental delays is based on a working knowledge of these domains and the typical age ranges for acquiring specific milestones within each domain. Therefore, the clinician should begin the evaluation of a child with developmental concerns by obtaining a developmental history, and emphasis should be placed on the pattern of milestone acquisition as well as the child’s current developmental skills. Clinicians working in a busy clinical setting may need to base this history primarily on the caregiver’s report of the child’s developmental abilities. Clinicians may also use standardized tools to aid in this portion of the history, including the Ireton Child Development Inventory (CDI), the Ages and Stages Questionnaire (ASQ), and the Parents’ Evaluation of Developmental Status (PEDS). However, if the clinician’s history confirms a developmental disability, standardized testing by a developmental specialist or clinical psychologist should be strongly considered; this formal evaluation will provide a much better assessment of the child’s developmental abilities.

When there is concern about developmental delay in a child, a developmental quotient should be calculated. The developmental quotient is the ratio of the child’s developmental age over the chronological age. The developmental quotient should be calculated for each developmental stream. Typical development is a developmental quotient greater than 70%, and atypical development it is a developmental quotient less than 70%. Toddlers and young children with atypical development are at risk for lifelong developmental problems. The term global development delay is used if a child younger than 5 to 6 years of age has a developmental quotient less than 70% in two or more domains. Children with global developmental delay should receive a thorough medical evaluation to try to determine the cause of the delay and begin management for their developmental disabilities.

Neurological and Other Medical History

For children with global developmental delay, the clinician should obtain a thorough medical history, including a detailed neurological history. Pertinent aspects of the history include the presence of any other neurological condition such as epilepsy, vision or hearing impairments, ataxia or a movement disorder, sleep impairment, and behavioral problems. The clinician should also inquire about prenatal, perinatal, and postnatal factors that can impact a child’s development (Tables 7.2 and 7.3). The social history should probe for environmental factors that can affect development, including physical or other forms of abuse, neglect, psychosocial deprivation, family illness, impaired personalities in family members, sociocultural stressors, and the economic status of the family.

Table 7.2 Etiology of Developmental Delay by Time of Onset

Prenatal/Perinatal	Examples
Congenital malformations of the CNS	Lissencephaly, holoprosencephaly
Chromosomal abnormalities	Down syndrome, Turner syndrome
Endogenous toxins	Maternal hepatic or renal failure
Exogenous toxins from maternal use	Anticonvulsants, anticoagulants, alcohol, drugs of abuse
Fetal infection	Congenital infections
Prematurity and/or fetal malnutrition	Periventricular leukomalacia
Perinatal trauma	Intracranial hemorrhage, spinal cord injury
Perinatal asphyxia	Hypoxic-ischemic encephalopathy
Postnatal	Examples
Inborn errors of metabolism	Aminoacidopathies, mitochondrial diseases
Abnormal storage of metabolites	Lysosomal storage diseases, glycogen storage diseases
Abnormal postnatal nutrition	Vitamin or calorie deficiency
Endogenous toxins	Hepatic failure, kernicterus
Exogenous toxins	Prescription drugs, illicit substances, heavy metals
Endocrine organ failure	Hypothyroidism, Addison disease
CNS infection	Meningitis, encephalitis
CNS trauma	Diffuse axonal injury, intracranial hemorrhage
Neoplasia	Tumor infiltration, radiation necrosis
Neurocutaneous syndromes	Neurofibromatosis, tuberous sclerosis complex
Neuromuscular disorders	Muscular dystrophy, myotonic dystrophy
Vascular conditions	Vasculitis, ischemic stroke, sinovenous thrombosis
Other	Epilepsy, mood disorders, schizophrenia

CNS, Central nervous system.

From Sherr, E.H., Shevell, M.I., 2006. Mental retardation and global developmental delay, in: Swaiman, K.F., Ashwal, S., Ferriero, D.I. (Eds.), Pediatric Neurology, Principles and Practice, fifth ed. Mosby, Philadelphia.

Table 7.3 Perinatal Risk Factors for Neurologic Injury

Maternal/Prenatal	Natal	Postnatal
Age <16 years or >40 years	Intrauterine hypoxia: prolapsed umbilical cord, abruptio placenta, circumvallate placenta	Abnormal feeding: poor sucking, weight gain, malnutrition, vomiting
Cervical or pelvic abnormalities	Midforceps delivery or breech presentation	Abnormal crying
Maternal illnesses: infection, shock, diabetes, nephritis, phlebitis, proteinuria, renal hypertension, thyroid disease, drug addiction, malnutrition	Poor Apgar scores: cyanosis, poor respiratory effort, bradycardia, poor reflexes, hypotonia	Abnormal exam: asymmetrical face, asymmetrical extremities, dysmorphic features, hypotonia, birth injuries, seizures
Maternal features: unmarried, uneducated, nonwhite, low-income, thin, short	Need for resuscitation: respiratory distress, bradycardia, hypotension	Abnormal findings: hyperbilirubinemia, fever, hypothermia, hypoxia
Consanguinity	Gestational age <30 weeks
Prior abnormal pregnancy, miscarriages, stillbirths, abortions, neonatal deaths, infants less than 1500 g, abnormal placenta	Vaginal bleeding in the second or third trimester
	Hypoxic-ischemic encephalopathy
	Polyhydramnios or oligohydramnios

Though families now typically have fewer children, and the caregivers’ knowledge of family history is frequently quite limited, the clinician should still make an effort to obtain a three-generation pedigree. The pertinent aspects of the family history include developmental disabilities, special education services or failure to graduate from school, neurodegenerative disorders, multiple miscarriages or early postnatal death, ethnicity, and consanguinity. If a specific genetic syndrome is suspected, the clinician should inquire about the presence in other family members of medical problems associated with that syndrome. For example, if the child has the features of fragile X syndrome, the family history should include questions about maternal premature ovarian failure, parkinsonism or ataxia of unknown etiology in the maternal grandfather, and intellectual disability or learning problems in an X-linked pattern.

Physical Examination

The growth parameters of the child should be measured, and the growth charts should be reviewed to determine the child’s rate of growth. This is pertinent because many chromosomal anomalies and other genetic disorders that cause global developmental delay and intellectual disability are associated with failure to thrive or short stature, large stature, microcephaly, and macrocephaly.

In the mental status portion of the examination, the clinician should note the interactions the child has with his or her caregivers and the clinician. Abnormal behaviors such as impaired eye contact, limited or absent social reciprocity, restricted or repetitive behaviors, and communication impairment may indicate that the child has an autism spectrum disorder, and the child should be referred to a psychologist for assessment or confirmation of this condition. Other abnormal behaviors such as hyperactivity, impulsivity, and inattention, as well as suboptimal parenting skills, may also be noted during these observations. However, the clinician should use caution when raising concerns about a behavior problem based solely on the child’s behavior in clinic, since this stressful situation may lead the child to manifest uncharacteristic behaviors.

A complete general physical and neurological examination should be performed to the extent the child will allow. The general examination should include but not be limited to an evaluation for dysmorphic features; abnormalities of the eyes (Table 7.4), skin, and hair; and organomegaly (Table 7.5). The neurological examination should include signs of impairment in extraocular movements; hypertonia or hypotonia; focal or generalized weakness; abnormal posture or movements; abnormal or asymmetrical tendon reflexes; ataxia, incoordination or other signs of cerebellar dysfunction; and gait abnormalities (see Table 7.5).

Table 7.4 Ocular Findings Associated with Selected Syndromic Developmental Disorders

Finding	Examples
Cataracts	Cerebrotendinous xanthomatosis, galactosemia, Lowe syndrome, LSD, Wilson disease
Chorioretinitis	Congenital infections
Corneal opacity	Cockayne syndrome, Lowe syndrome, LSD, xeroderma pigmentosa, Zellweger syndrome
Glaucoma	Lowe syndrome, mucopolysaccharidoses, Sturge-Weber syndrome, Zellweger syndrome
Lens dislocation	Homocystinuria, sulfite oxidase deficiency
Macular cherry-red spot	LSD, multiple sulfatase deficiency
Nystagmus	Aminoacidopathies, AT, CDG, Chédiak-Higashi syndrome, Friedreich ataxia, Leigh syndrome, Marinesco-Sjögren syndrome, metachromatic leukodystrophy, neuroaxonal dystrophy, Pelizaeus-Merzbacher disease, SCD
Ophthalmoplegia	AT, Bassen-Kornzweig syndrome, LSDs, mitochondrial diseases
Optic atrophy	Alpers disease, Leber optic atrophy, leukodystrophies, LSDs, neuroaxonal dystrophy, SCD
Photophobia	Cockayne syndrome, Hartnup disease, homocystinuria
Retinitis pigmentosa or macular degeneration	AT, Bassen-Kornzweig syndrome, Cockayne syndrome, CDG, Hallervorden-Spatz syndrome, Laurence-Moon-Biedl syndrome, LSD, mitochondrial diseases, Refsum disease, Sjögren-Larsson syndrome, SCD

AT, Ataxia-telangiectasia; CDG, congenital disorders of glycosylation; LSD, lysosomal storage diseases; SCD, spinocerebellar degeneration.

Table 7.5 Other Findings Associated with Selected Syndromic Developmental Disorders

Finding	Examples
Cerebellar dysfunction	Aminoacidopathies, AT, Bassen-Kornzweig syndrome, CDG, cerebrotendinous xanthomatosis, Chédiak-Higashi syndrome, Cockayne syndrome, Friedreich ataxia, Lafora disease, LSD, Marinesco-Sjögren syndrome, mitochondrial disease, neuroaxonal dystrophy, Pelizaeus-Merzbacher disease, Ramsay Hunt syndrome, SCD, Wilson disease
Hair abnormalities:
Synophrys	Cornelia de Lange syndrome
Fine hair	Homocystinuria, hypothyroidism
Kinky hair	Argininosuccinic aciduria, Menkes disease
Hirsutism	LSD
Balding	Leigh syndrome, progeria
Gray hair	AT, Chédiak-Higashi syndrome, Cockayne syndrome, progeria
Hearing abnormalities:
Hyperacusis	LSD, SSPE, sulfite oxidase deficiency
Conductive loss	Mucopolysaccharidoses
Sensorineural loss	Adrenoleukodystrophy, CHARGE, Cockayne syndrome, mitochondrial diseases, SCD, Refsum disease
Infantile hypotonia	Canavan disease, myopathies, LSD, Leigh syndrome, Menkes disease, neuroaxonal dystrophy, spinal muscular atrophy, Zellweger disease
Limb abnormalities:
Micromelia	Cornelia de Lange syndrome
Broad thumbs	Rubinstein-Taybi syndrome
Macrocephaly	Alexander disease, Canavan histiocytosis X, LSD
Microcephaly	Alpers disease, CDG, Cockayne syndrome, incontinentia, pigmenti, neuronal ceroid lipofuscinoses, Crabbe disease, neuroaxonal dystrophy, Rett syndrome
Movement disorders	AT, LSD, dystonia musculorum deformans, Hallervorden-Spatz, juvenile Huntington disease, juvenile Parkinson disease, Lesch-Nyhan disease, phenylketonuria, Wilson disease, xeroderma pigmentosa
Odors:
Cat urine	β-Methyl-crotonyl-CoA carboxylase deficiency
Maple	Maple syrup urine disease
Musty	Phenylketonuria
Rancid butter	Methionine malabsorption syndrome
Sweaty feet	Isovaleric acidemia
Organomegaly	Aminoacidopathies, CDG, galactosemia, glycogen storage diseases, LSD, Zellweger syndrome
Peripheral neuropathy	AT, Bassen-Kornzweig syndrome, cerebrotendinous xanthomatosis, Cockayne syndrome, LSD, Refsum disease
Short stature	Cockayne syndrome, Cornelia de Lange syndrome, hypothyroidism, leprechaunism, LSD, Prader-Willi syndrome, Rubinstein-Taybi syndrome, Seckel bird-headed dwarfism
Seizures	Aminoacidopathies, CDG, glycogen synthetase deficiency, HIE, LSD, Menkes disease, mitochondrial diseases, neuroaxonal dystrophy
Skin abnormalities:
Hyperpigmentation Hypopigmentation	Adrenoleukodystrophy, AT, Farber disease, neurofibromatosis, Niemann-Pick disease, tuberous sclerosis complex, xeroderma pigmentosa
Nodules	Chédiak-Higashi syndrome, incontinentia pigmenti, Menkes disease, tuberous sclerosis complex
Thick skin	Cerebrotendinous xanthomatosis, Farber disease, neurofibromatosis, LSD, Refsum disease,
Thin skin	Sjögren-Larsson syndrome, AT, Cockayne syndrome, progeria, xeroderma pigmentosa

AT, Ataxia-telangiectasia; CDG, congenital disorders of glycosylation; CHARGE, coloboma, heart disease, choanal atresia, retardation, genital anomalies, ear anomalies; HIE, hypoxic-ischemic encephalopathy; LSD, lysosomal storage diseases; SCD, spinocerebellar degeneration; SSPE, subacute sclerosing panencephalitis.

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