Achondroplasia, also known as dwarfism, has easily recognisable features: short legs and arms, prominent forehead, protruding jaw and a flat or concave area between the eyes. A genetic mutation affecting 1 in 25,000.
Narrowed ear and nasal passages mean more ear infections and breathing problems in childhood. Physical developmental milestones take longer to reach. Legs generally become bowed as children grow. Intellectually, they are normal, but chairs, cloakroom hooks, door handles etc will need adapting. Adolescents may need social and emotional support.
Fragile X affects both girls and boys. Caused by a malfunction of the X chromosome, but because girls have two, one of which works normally, impact is much greater on boys. A typical male would be inattentive, easily distracted, impulsive and overactive. Girls generally have less challenging behaviour but similarly poor attention. They are often shy and withdrawn, dislike eye contact and are anxious in social situations. This may result in hand-flapping, biting or tantrums. Speech and language may be delayed, although academic performance varies greatly. Some have prominent ears, their only physically distinguishing feature, so diagnosis can be very late. www.fragilex.org.uk
Hunter Syndrome is carried by females but appears only in males. They lack an essential enzyme that breaks down a normal but potentially dangerous chemical. First indications appear around two: an enlarged skull and facial features, stiffening joints and increased body hair. Hearing, vision and intellectual capacity then deteriorate; they become hyperactive and possibly aggressive. Most heart and other organ defects. They die between the ages of 10 and 20. www.mpssociety.co.uk
Klinefelter's Syndrome affects one in 1,000 boys who have an extra X chromosome. Some show no symptoms until they discover infertility in adulthood. Others have moderate learning difficulties, poor speech and communication, shyness, poor attention span or social immaturity. Many have prominent teeth but thin enamel, so are at high risk of tooth decay. At puberty, some boys experience the same broadening of the hips that girls do. They may develop breasts, so PE is embarrassing. Testosterone treatment andor surgery can also have emotional consequences. www.ksa-uk.co.uk
Neurofibromatosis causes tumours (almost always non-malignant) anywhere in the body. Affects one in 4,000 children. Growths that make sufferers look like the Elephant Man (although he had the rarer Proteus Syndrome) become evident by 10. They can be detected and surgically removed, but can recur.
Tumours in the head cause tinnitus (ringing in the ear), deafness, poor balance and, in extreme cases, strokes or death. Tumours elsewhere cause physical disability. Intellectual abilities are unaffected, but pain, missed school or hearing loss may undermine learning, as may self-consciousness about their appearance. Life expectancy for most is normal. www.nfauk.org
Prader-Willi Syndrome usually stems from an accidental chromosomal abnormality, so rarely runs in families. Affects one in 20,000. Children have weak muscle tone and physical sensitivity, tiring easily and sometimes even breaking limbs without noticing. They may have mild, moderate or severe learning difficulties, below-average height, lack of normal sexual development, emotional instability and lack of maturity in social skills.
From two, they develop a continual urge to eat, because their appetite-control system fails. Uncontrolled, it can lead to extreme weight gain, but physiotherapy and exercise help many live beyond middle age.
Rett Syndrome affects 1 in 10,000 girls, who appear to develop normally, sitting and even speaking single words, before deterioration around their first birthday. Communication and hand movements become rigid and stereotyped; many appear to lose control of their bodies, so they cannot make their limbs, or even their eyes, move. Some have seizures. Some walk then lose the ability; others learn in adolescence; others never walk at all. Many are very sociable. Learning abilities are thought to range widely, but without control over hand and eye movement or speech, these are hard to assess. www.rettsyndrome.org.uk
Williams Syndrome Symptoms include distinctive facial features: small upturned nose, long upper lip, small chin, puffiness around the eyes, widely spaced, small, teeth. Heart problems are common. Sufferers have highly sensitive hearing; loud noise can be painful or startling. They have uneven intellectual profiles: unusually expressive language, good long-term memory and social skills, but poor fine motor skills and spatial awareness.
Many sleep badly and are easily distracted, making it difficult to assess their learning abilities. Their extreme friendliness means they will wander off and speak to strangers. Affects around 1 in 20,000 of both sexes. Life expectancy normal.