Monosomy 1p36 Deletion Syndrome
1p36 deletion syndrome is a chromosome disorder. A chromosome disorder is a change in chromosome number or structure which results in a set of features or symptoms. People with 1p36 deletion syndrome have lost a small but variable amount of genetic material from one of their 46 chromosomes.
1p36 deletion syndrome was described for the first time in the late 1990s, although the first case of a child with a deletion of 1p36 was published in 1981.
Most reports suggest that 1p36 deletions affect girls more often than boys – around 65 per cent of reported cases are girls. Unique families support this: 73 per cent of the children with 1p36 deletion syndrome are girls. The reasons for this are, as yet, not known.
Most likely features
The effects of 1p36 deletion syndrome vary between individuals. Children will not necessarily have all of these features but they have been found to be the most common.
* Developmental delay
* Children need support with learning. The amount of support needed by each child will vary, although most benefit from attending a special school
* Hypotonia (floppiness), especially in babies, but this may persist
* Feeding difficulties
* Cardiomyopathy (disease of the heart muscle) and minor heart defects
* Hearing loss and vision defects
* A large soft spot (fontanelle) at birth that is slow to close
* Distinctive facial appearance
How might a 1p36 deletion alter a child’s ability to learn?
All children studied so far have shown some degree of learning disability, usually in the moderate to severe range. Many parents report that the most effective learning strategies include music, lights, visual learning and books, especially tactile ones. Patience, repetition and lots of praise and encouragement are important. Some children have found a touch screen computer a useful learning aid. Some children learn to draw simple lines and shapes, read and write. Parents note that many children have good memories, particularly for faces and places.
How might 1p36 deletion affect my child’s ability to communicate?
Delayed or absent speech has been reported in 98 per cent of children. From around 3 years, some master a signing system, although for those with persistent hypotonia this can be difficult. Some children use a few words, and a minority of children may develop some complex speech. Three of the 25 Unique children surveyed can make simple three or four word sentences. For many children, receptive language is markedly better than their expressive language skills – they understand far more than they are able to express.
How can a 1p36 deletion affect a child’s development and mobility?
Babies with 1p36 deletion syndrome have a characteristic pattern of motor development. In their second year many start to roll, at first onto their side but eventually from back to stomach. For most toddlers, rolling, twisting and wriggling remained the favourite way to move until they became strong enough to sit. Head control started to improve in the second and third years and some babies could pull to sit if supported. Sitting independently was achieved among Unique children at an average age of 24 months to 5½ years. Most babies never crawl, typically rolling or bottom-shuffling instead. Standing and walking are skills that children with 1p36 deletion syndrome find especially challenging, often despite years of practice and training in standing frames and walkers and using ankle/foot orthotics. Once mobile, some children go on to run, climb, dance and even ski. However, walking may not prove possible for all. A small number do not master sitting unaided and require the use of special supportive seating. The floppiness (low muscle tone or hypotonia) that is one cause of this severe motor delay is usually obvious from birth, affects nine out of 10 babies, and gradually improves with age and physiotherapy.
Hand-eye co-ordination and dexterity (fine motor skills)
Fine motor skills can also be seriously affected, making holding objects such as toys, cutlery and cups very difficult. Achieving milestones such as holding a cup or spoon are therefore often delayed, with many children needing special cutlery and cups. Older children may find holding pencils and pens difficult. Poor fine motor skills can also make mastering sign language more challenging.
Children with a 1p36 deletion have a distinctive, if subtle facial appearance: typically, a small head (microcephaly), large, rounded forehead (frontal bossing), a small, pointed chin, low set and unusually formed ears, eyes set in well defined sockets under straight eyebrows and a flat nasal bridge.
Growth and Feeding
Some children, but not all, are very small for their age. Some babies are born short and grow slowly so that small size can be a marked feature of a 1p36 deletion. Feeding problems are common in newborn babies. Two-thirds of babies in one study either sucked too weakly to meet their nutritional needs or had difficulties co-ordinating sucking with swallowing. Swallowing studies have shown dysfunction in almost three quarters of babies and swallowing difficulties and choking mean that both breast or bottle feeds can take a long time. Some babies have benefited from a temporary nasogastric (NG-tube, passed up the nose and down the throat) or gastrostomy tube (a G-tube, feeding direct into the stomach). Gastro-oesophageal reflux (in which feeds return readily up the food passage) and vomiting are also common in babies and young children. In the Unique survey, over 70 per cent of babies had reflux. Feed thickeners and prescribed medicines to inhibit gastric acid may control reflux but some babies benefit from a fundoplication, a surgical operation to improve the valve action between the stomach and food passage. Sixty-one per cent of Unique families surveyed reported constipation, occasionally very severe.
What are the medical concerns?
Children with 1p36 deletions have a variety of treatable medical problems. Left untreated, these can compound the child’s difficulties.
Studies suggest that heart (cardiac) problems occur in most os 1p36 of children. Approximately 30 per cent of the heart problems were cardiomyopathy, where the heart is enlarged and doesn’t pump as strongly as it should, and around 70 per cent had structural defects. Cardiomyopathy may require medication but may also gradually improve over time. In the Unique survey, 54 per cent of children had cardiac problems.
Hearing loss affects around two thirds of people with 1p36 deletion syndrome. It can vary from mild loss at various frequencies to severe loss at all frequencies. There is evidence that the loss is progressive in some children, so an annual hearing check is recommended. The hearing loss can be sensorineural (caused by damage to the inner ear or to the nerve used for hearing) or conductive (associated with the function of the outer or middle ear). Sensorineural hearing loss is permanent and is usually treated with hearing aids, or for those more severely affected, cochlear implants. The conductive hearing loss is temporary and due to glue ear (a build up of fluid in the middle ear). Glue ear resolves itself as children get older and the ear tubes widen resulting in improved drainage of the middle ear. However, while glue ear persists, many children will need grommets (a small ventilation tube) inserted into the ear. Alternatively, hearing aids may be used for the duration of the glue ear. Among Unique families, eight out of 14 children with hearing loss had conductive deafness.
Vision problems are very common and variable. Around 80 per cent of children have been found to have some vision defect. The problems can be due to the structure and function of the eyes, or problems with the brain processing the information received from the eyes. Other eye problems that have been found include optic disc atrophy, short or long sightedness, nystagmus, photosensitivity (photophobia), cataracts and astigmatism. Glasses can help or correct a number of these problems, and for those with photosensitivity, photochromic glasses have helped enormously. In addition to problems with the eye itself, some children suffer from cortical visual impairment, where the visual systems of the brain do not consistently understand or interpret what the eyes see. Whatever the cause of the vision impairment, the problems can be severe, two thirds of children are visually inattentive and unable to fix or follow movements
Seizures affect around half to three quarters of all the children. Onset of seizures ranged in the Unique survey from birth to 3 years (the medical literature cites seizures starting from 4 days of age to 7 years). For most children the seizures are relatively well controlled with medication. There are some children, however, for whom their epilepsy is extremely difficult to control, despite multiple medications. In two of the Unique families, the seizures evolved into Lennox-Gastaut syndrome, an uncommon form of epilepsy that is difficult to treat.
Children with marked hypotonia are sometimes prone to develop a spinal curve, such as kyphosis (forwards curve) or scoliosis (sideways curve). The literature reports scoliosis in 16 per cent of children, whereas in the Unique survey 30 per cent of children had spinal curvature. A small number have needed surgery to correct the curvature, whereas for others posture management such as a spinal brace or jacket, good seating and a sleep system (a special bed which offers support for the spine and keeps the child in a good position during sleep) have been necessary. Physiotherapy has also been effective for some children.
A few children have been reported with kidney defects. Among Unique members these include kidney reflux, a single kidney, an accumulation of calcium in one kidney and kidney stones
Studies have indicated that around one child in five has been found to have a low thyroid hormone level (hypothyroidism) and to need thyroxine replacement and it is suggested that all children should be monitored for thyroid function.
A variety of genitourinary disorders have been reported. Minor anomalies of the genitals are common in babies with chromosome disorders, most often affecting boys. According to one report, 25 per cent of children with 1p36 deletions are affected, having problems such as undescended testes (cryptorchidism), and underdeveloped scrotum and genitalia in boys. The Unique survey revealed that 50 per cent of boys have small genitals and 38 per cent have undescended testes (which can be brought down by a straightforward surgical procedure).
There are very few reports on adolescents, but it seems that in either sex puberty may start early. Other reports suggest that some children never become fully sexually mature adults. Amongst the Unique families, puberty took place in girls most often between the ages of 9 and 11 years.
Two thirds of Unique’s children with a 1p36 deletion suffer from recurrent infections whose range and nature suggest some degree of immune compromise. Fourteen children have had repeated pneumonias and four contracted meningitis. Chest infections, colds and gastroenteritis are all common, often longer lasting than in typically developing children.
Hands and feet
Small hands and feet are common in children with 1p36 deletion syndrome. A number of other hand anomalies have been described including one or both hands with a single palm crease (instead of the usual two), fingers and/or toes with either one crease or three creases (instead of the usual two), and incurving fingers (clinodactyly), most frequently the 5th finger. Some families reported clenched fists in young children, which can be a sign of neurological compromise or damage. Daily exercises and sensory play proved successful in helping the hands to open. Unusual features affecting the feet have also been reported, including flat feet, talipes (clubbed feet) and overlapping toes. A number of children wear supportive footwear, orthotics or splints to help overcome these problems.
In general, children with a 1p36 deletion are placid and affectionate. However, they are as vulnerable to frustration as other children with a communication difficulty and temper tantrums and aggression can present carers with challenges. Behavioural problems have been reported in as many as 50 per cent of children and the evidence from Unique seems to back up this figure. The behavioural issues are wide-ranging. A number of children are extremely shy in new situations and have difficulty making eye contact, especially with people they don’t know. Conversely, others can be overly affectionate, including with strangers. Evidence from Unique suggests that sensory difficulties can be problematic for some children. This can be tactile defensiveness, where children are sensitive to touch (with some children finding it hard to have their hands and/or feet touched or their hair washed and brushed) or sensitivity to certain textures. Some children go through a long phase of chewing or biting their own hands, arms and wrists, and occasionally other people’s, usually when in pain, tired, frustrated or frightened but on occasion for no obvious reason. This can be hard to stop without actual physical intervention, although some parents have found arm splints that act as restraints or a chewable object attached to their child’s clothes to be helpful. Head banging and hitting their own head is less common. Parents suggest that these traits may be linked to a high pain threshold. There have also been some reports of autistic behaviours in children with 1p36 deletion syndrome.
What is the outlook?
It is difficult to predict the long-term outlook for an individual child. There is only one study to date in which the natural history of 1p36 deletion syndrome has been investigated with a follow-up spanning 18 years.
Unique’s experience has been that children will normally need lifelong care and medical support and will at best achieve only limited independence. Parental experience suggests that a small minority of children achieve toilet timing or toilet training. Many can help get themselves dressed by pushing their arms through sleeves and a few learn to undress but almost all need a carer for dressing. Some children are able to brush their teeth and wash their hands and faces, although the majority need help with these tasks.