A) Retinal disorders

About 90% of children with Bardet-Biedl or Laurence-Moon Syndromes develop a detectable retinal disorder (sometimes called retinitis pigmentosa [RP] or tapetoretinal dystrophy [TRD]).  [By adolescence, this becomes 100%] This disorder causes a loss of function in the retina.  The most prevalent of TRD is retinitis pigmentosa.  The image of an object that we view is projected onto the retina by the lens of the eye.  Somewhat like the film in a camera, the retina “translates” these light images into electrical impulses and sends them to the brain.  This change of light into electrical impulses occurs in specialized retinal cells, called rods and cones.  All the signals of the 300 million light-sensitive cells in each retina enable the brain to interpret or “see” the object.  Rods and cones are not distributed in a haphazard fashion in our retina.  Cones are concentrated in the center of the retina and rods are distributed around the periphery.  We use the cones for fine vision (reading, recognizing faces) and to distinguish colors.  Rods are used in low light situations. 

Retinal disorders are divided into three groups.The names and the descriptions are,arbitrary,general,and non-specific:

In the first group, the rods are primarily affected first.  Vision in low light conditions becomes difficult and later still, impossible.  In addition, the visual field is profoundly lost (tunnel vision).  As long as the central retina, with the cones, still functions, central vision will remain untouched.  For people with this form of retinal dystrophy, also called “retinitis pigmentosa”, it is like looking through a tube.  Symptoms include loss of dim light vision and loss of peripheral vision, tripping over thresholds, steps, toys, and other obstacles that cannot be seen due to the increasing limitations of the visual field.  Eventually it is possible that the cones also become involved in this process, leading severe loss of vision.

And last, a third group exists, in which both rods and cones are affected equally.  This is sometimes called a “mixed tapetoretinal degeneration”. 

B) Night blindness

Retinal dysfunctions in Bardet-Biedl and Laurence-Moon Syndromes are often first identified because the child (some early, but usually later in the first decade) displays signs of night blindness.  The child sees poorly at night or during the day indoors or in low-light situations.  A steady diminishing of the visual field occurs as the child gets older.  During puberty the marked reduction of vision is obvious.  About three-quarters of adults with these syndromes have poor vision (legally blind).  Since the retinal features may be subtle to the examiner of a child, the presence of this dysfunction may be determined at an early stage with the help of an Electroretinogram (ERG).

A) Obesity

Obesity occurs in approximately 80% of the children and adults.  It is not congenital, but tends to develop in the later part of the first year of life when babies and toddlers start gaining weight too fast.  Often this is not taken seriously, even when parents comment about it.  Around the ages of 3 or 4 years, the obesity becomes obvious.  Usually the child’s appetite is not greater than normal.  The accumulation of fat is usually around the mid-section (central obesity) – the stomach, hips and pelvis areas, but the face can also give a round or “fat” appearance.  Many children have so-called “pillows” of fatty tissue on top of their hands and feet.  Without dietary and exercise assistance, obesity will continue to worsen and be a serious problem after puberty.  With substantial obesity at an early age there is an increased chance of diabetes and problems with weight-bearing joints.  These concerns should encourage dietary measures at an early age.  This obesity may be (but not necessarily) accompanied by shortened stature.

B) Under-developed sexual organs (Hypogonadism)

Under-development of the sexual organs (hypogonadism) occurs in approximately 85% of males and 45% of females.  Hypogonadism may be difficult to confirm in infants.  Usually the male genitalia are very small.  The size of an obese boy’s penis is hard to determine, because the penis often disappears in subcutaneous fatty tissue.  It is easier to measure the size of the testes.  These are typically small and often are not descended into the small scrotum.  There is a large variation in the development of secondary sexual signs at puberty.  Normal development of semen, sperm, and erectile function and therefore normal fertility, has occurred in some males, but in others this seems to be missing.  Females display a different pattern of underdevelopment of the sexual organs.  Sometimes, anomalies of the vagina, bladder, and urinary tracts are present at birth (called hydrometrocolpos).  A common reason for examination (if there are no outwardly noticeable signs) is late onset of the menstrual cycle or irregularities or complete absence of monthly cycles.  The first menstrual cycle normally occurs between the ages of 13 and 17 years, later than unaffected siblings.  Most females have been found to have normal fertility.

C) Skeletal anomalies

About 90% of Bardet-Biedl Syndrome children have congenital abnormalities of hands and feet.  Polydactyly, the occurrence of extra fingers and toes, is seen in more than three-quarters of BBS children.  There is an extra toe on one or both feet or an extra finger on one or both hands.  These “extras” are usually on the outside, lateral side, of the hand or foot.  Rarely there are even two extra toes.  Another variation is a finger or toe that is “double: (two partially grown-together thumbs, for example).  The most common variation is a partial joining at the base of the second and third toes.  Usually, the abnormality is symmetrical, meaning that the abnormality on the right side is similar to the one on the left side.  The hands of children with Bardet-Biedl Syndrome are usually short and relatively broad, with short, slightly curved fingers.  Polydactyly is an important sign because it is noticed immediately after birth.

D) Renal problems

Kidney abnormalities occur in 75-95% of the people with Bardet-Biedl Syndrome.  Medical professionals must be aware of this.  Apparently the primitive kidney does not mature enough in development during pregnancy.  Other kidney problems are polycystic kidneys, irregularly shaped kidneys, and occasionally small kidneys.  Since the kidneys may not function well because of these abnormalities (the filtration of waste products and concentrating them into urine), it is possible that too many waste products remain in the bloodstream (the medical term is “uremia”) and too much liquid is voided with the urine.  This leads in turn to an increased volume of urine, which in turn causes excessive drinking (polydipsia and polyuria).  The recognition of kidney involvement with Bardet-Biedl Syndrome is fairly recent.  Because kidney abnormalities can be present for years before they actually causes medical problems, many adult BBS patients have less-than-normal kidney function.  Therefore, part of the periodic diagnostic surveillance should include testing of the kidney function, including urinalysis, blood tests of byproducts in the blood stream, and even ultrasound or imaging of the kidneys.  Regular follow-up is requisite.  End-stage kidney failure happens in a minority of adults with Bardet-Biedl Syndrome, some of whom may ultimately need dialysis and transplants.

E) Neurological manifestations

Neurological manifestations are uncommon in BBS patients, but more prevalent in patients with Laurence-Moon Syndrome.  However, the number of patients worldwide with Laurence-Moon Syndrome is so small that knowledge of this spectrum is limited.  Children with Laurence-Moon Syndrome display poor coordination and staggering (ataxia) during the first years of life, for example, while walking.  Slowly but surely these signs increase and contracting (spastic) muscles manifest themselves later on.  During puberty about one-third of Laurence-Moon Syndrome patients develop true spasticity that worsens with time.  Eventually adults can be wheelchair or bed-bound.  Rarely, epilepsy (seizures) may occur in young children with Laurence-Moon Syndrome or BBS.  Anomalies in an EEG (brain wave test) occur more often.

F) Dental Anomalies

In a Norwegian survey of 30 patients with Bardet-Biedl Syndrome, ranging in age from 4 to 60 years, a large fraction of them displayed specific dental anomalies, including short roots, especially in the front upper teeth, degeneration of the enamel, and increased infection of the gums.  However, the level of dental education, self-care, and hygiene may be problems.  It is therefore advisable to have a careful assessment and regular monitoring by a dentist, an orthodontist, and/or a hygienist.

G) Other Physical Characteristics

Some children display other physical characteristics associated with these syndromes. Although rare, we mention them here briefly.

• “Knock-knees”, often paired with “flat feet” with no arch
• Clubbed feet and other deformities of the feet
• Deformities of the spinal column and hips (including curvatures)
• Cleft palate
• Congenital heart defects
• Atresia ani ( the rectal opening is absent)
• Thyroid and liver dysfunction

A) Educational Development

Developmental delay has been considered one of the primary signs of both syndromes.  More recently it has become evident that a relatively large minority (approximately 40%) of patients have an average intelligence.  The remaining 60% have mild to moderate learning disabilities.  Children are often misdiagnosed due to their passivity and a lack of motivation to acquire knowledge.  Their interest can be stimulated, but this takes time and encouragement.  Remarkable is their concrete level of thinking.  This manifests itself especially clearly in daily living circumstances.  Skills for accurate assessment in social circumstances and self-image are usually less than normal.  The adult with either of the two conditions often has difficulties with organization and planning.  Rather than be productive, they prefer to be re-productive: in other words, they prefer to copy rather than to produce an original essay; they prefer to copy a painting or picture rather than to draw something original; they would prefer to do a jig-saw puzzle than to create something from scratch.  The “learning and remembering” process seems to function well.  Motivation to be praised in scholastic activities is great.  Their perseverance to get something accomplished is great.

B) Social-emotional Development

Children and young adults with Laurence-Moon or Bardet-Biedl Syndromes are usually compliant by nature but may not have a lot of patience and can be stubborn.  Often they are friendly, quiet children. But hey can be fearful, sensitive, and emotionally unstable.  They display little enthusiasm for new experiences and prefer to be occupied with familiar activities.  The fear for new experiences is strengthened by their (literal) difficulty to see and understand situations.  An exaggerated reaction to relatively minor circumstances is especially apparent in children and young adults.  If the child is upset, he or she can remain that way for a long time.  It appears to be lacking internal controls to stop this mood swing.  Sometimes it is possible to bring the child out of this emotional turmoil by directing his or her attention to something different.  Another way to alleviate these emotional turmoils is to help the child verbalize his or her feelings about the situation.  The child is not capable of doing this on his own, but with assistance and patient encouragement success can be achieved.  Another consequence of this concrete thinking is that the children have a strong need for regularity and clarity in their daily lives.  They may be difficult to divert from regular patterns and customs, and they are not flexible when different circumstances present themselves.  A change from the daily routine can wreak havoc with their emotional stability.  Social contacts with peers can be difficult.  They prefer to socialize with younger children who appear to be more equal to them both developmentally and socially.  They also require intense contact and approval from adults.  A child with either of these disorders will most often be passive in his or her interaction with others.  They prefer to avoid conflicts: they either give in or withdraw.  Open aggression is uncommon in children with these disorders.  They often can react angrily by screaming/crying or by being stubborn, especially in the teenage years.  The early night blindness may be accompanied by fear of darkness or “night terrors” requiring night lights in the bedroom.  The fear of going blind is therefore real in most children.  Dealing emotionally with the increasing loss of vision is extremely difficult.  Many also have problems with learning to use a guide cane. It takes time to become emotionally ready for this step.

< top >

© Copyright 2001. All rights reserved.
Contact: Webmaster