10.3 The dysmorphic child
Dysmorphic, which literally means ‘abnormal form’, refers to an unusual appearance, usually of the face. A dysmorphic child may have an underlying diagnosis that could have implications for the health not only of the child but also of other family members if the condition is inherited. With the advent of new genetic testing options such as array comparative genomic hybridization (‘microarray’) and an upsurge in commercially available tests for single-gene disorders, our understanding of the genetic basis underlying the dysmorphic child is improving all the time. The dysmorphic child may present as a neonate with one or more birth defects (e.g. a missing hand), or later with developmental delay or intellectual disability, failure to thrive or obesity, short or tall stature, a behavioural disturbance or a metabolic problem.
Birth defects can be classified as deformations, disruptions, dysplasias or malformations (see Chapter 10.1). It is important to distinguish between abnormalities and minor variants that are common in the general population. These can, however, appear in syndromes. For example, a unilateral single transverse palmar crease is seen in 4% of normal people but is more common in Down syndrome. Some physical traits, such as an unusually shaped nose, are a harmless family variant but again could be part of an undiagnosed syndrome in the family.
• Syndrome. This is from the Greek ‘running together’ and refers to a cluster of physical and other features occurring in a consistent pattern, with an implied common specific cause that may be unknown. The word syndrome is often used loosely to describe any of the other diagnostic patterns described below.
• Association. This is a group of physical features that tends to occur together but the link is not consistent enough to allow the term syndrome to be used. An example is the VATER association (see below). The distinction between a syndrome and an association may be artificial and, increasingly, associations are being redefined as syndromes as their genetic basis is identified. For example, in 2004 CHARGE association (Coloboma, Heart defects, Atresia choanae, Retardation of growth and development, Genital and Ear anomalies) was identified as being due to mutations in the CHD7 gene on chromosome 8; with this, CHARGE association became CHARGE syndrome.
• Sequence. This refers to a group of abnormalities caused by a cascade of events beginning with one malformation. An example is the Potter sequence, which can result from any cause of severe oligohydramnios. For example, renal agenesis results in no fetal urine, leading to severe oligohydramnios, with the consequence of lung hypoplasia and intrauterine constraint, causing limb deformities, such as talipes, and a compressed facial appearance.
• Developmental field defect. This refers to a group of malformations caused by a harmful influence in a particular region of the embryo. Abnormalities of blood flow are thought to underlie many of these. An example is hemifacial microsomia with unilateral facial hypoplasia and ear anomalies relating to an abnormality in development of first and second branchial arch structures.
• The diagnosis must be correct: the diagnosis may be based on clinical assessment alone with no confirmatory tests available; diagnosis must not be undertaken lightly as it can be difficult to remove or alter a diagnosis once it has been made, with harmful consequences for the child and family.
A ‘waiting room diagnosis’ based on the facial ‘gestalt’ might be made if the doctor has seen a person with the particular syndrome before, just as most people are able to recognize whether a person in the street has Down syndrome. Often, however, the diagnosis is not apparent initially, and the following approach is recommended.
Family history – draw a three-generation family tree noting miscarriages, stillbirths and deaths of siblings, any history of intellectual disability, congenital abnormalities or consanguinity (i.e. are the parents related?), and enquire about other family members with the same features.
• always plot measurements on standard normal charts. Charts are available for many different body parts (e.g. hand measurements, foot and ear length). Special charts are available for certain disorders (e.g. Down syndrome) and various bone dysplasias (e.g. achondroplasia)
Fig. 10.3.1 Normal human face: list of common terms used in dysmorphology. (A) 1, Supraorbital ridge; 2, outer canthus; 3, inner canthus; 4, palpebral fissure (line from inner canthus to outer canthus); 5, nasal root; 6, nasal bridge; 7, nasal tip; 8, naris/nares; 9, columella; 10, philtrum; 11, nasolabial fold; 12, upper vermillion border of lip. (B) Lateral view: 13, line indicating normal ear height – the superior attachment of the pinna should lie above an imaginary line drawn through bo;;th inner canthi and running posteriorly; ‘low-set’ ears are below this line; 14, lobule; 15, helix; 16, tragus; 17, antihelix.
• Check textbooks of syndromes (e.g. Smith’s Recognizable Patterns of Human Malformation) by trying to match the most important dysmorphic features and comparing the photographs with those of the patient.
• It’s not easy! A skilled dysmorphologist makes a syndrome diagnosis in a dysmorphic child in about 30% of cases referred by an experienced paediatrician. If an overall diagnosis is not made, the recognized problems must still be managed.