Category Archives: Genetics

Prader Willi syndrome

Chromosome 15q11 related. Results from deletion of paternal copy of imprinted gene (the rare genes where the copy from one parent is turned off by DNA methylation). See also Angelman syndrome (also chromosome 15).

Beware pregnancies with Trisomy 15 where subsequent testing looks like normal diploid…

Classically severe hypotonia at birth, often with mild growth restriction, causing significant feeding difficulties.

Facial appearance characteristic even at birth: high forehead, narrow bifrontal diameter, downturned corners of the mouth, micrognathia, and dysplastic ears. As they age, almond eyes become apparent, face is rather unexpressive of course. Hands are small.

After age 1, ironically, appetite then seems to surge, leading to obesity.

Scottish genomic test directory says test if:

  • Severe hypotonia and/or feeding difficulties in early infancy;
  • Global developmental delay;
  • Hypogonadism;
  • Excessive eating with central obesity if uncontrolled in childhood

Rare Disease

EU definition – less than 1 in 2000 people affected.  But at least 7000 described. So prob 3.5 million in the UK, and lifetime risk 1 in 17?

Most present in childhood. And 30% will die before age 5…

9 rare diseases tested for at birth so drop in the ocean… Some US states test over 45…

Average delay in diagnosis in UK patients is 5.6 years, with average of 4 different primary care and 4 secondary care clinicians! https://globalgenes.org/wp-content/uploads/2013/04/ShireReport-1.pdf

Dare to think rare!

Common challenges –

  • Misdiagnosis
  • Inappropriate treatment
  • Passing between specialties
  • Having lived experience denied or not listened to
  • Then having to become advocates +/- carer
  • Diagnostic criteria can be unclear
  • Stigma – outward appearance or misconceptions
  • Cf invisible conditions – “doesn’t look disabled”
  • Poor coordination of care. Role of primary care unclear.
  • “Burden of explanation” and lack of knowledge in professionals
  • Transition
  • Guilt (where genetic)
  • Mental health (chronic illness or underlying disease)

Diagnostic “odyssey” – unfathomable obstacles. Often labelled functional (or worse…), and parents as “anxious”, “demanding”.

Doctors tend to force a common diagnosis on to symptoms/signs that don’t quite fit.

Parents struggling with a sick child may delay having other children, may spend out on private treatment or move to different areas/countries to seek care, lose earnings/educational attainment, and family relationships suffer.

Once diagnosis is made, life begins with health issues being only 1 part of the whole picture rather than defining life. And provides access to experts and family support all over the world.

Become expert patients/families. Patient organisations offer support but also advocacy, research

No treatment is not no management

Not knowing the condition doesn’t mean you can’t listen and try to understand, or that you can’t coordinate things (esp when multiple teams/professionals involved).

Some will be happy to disclose/discuss diagnosis  – others may get bored and frustrated at times – and may be stigma

Primary care and emergency departments gain very little confidence. Hospital staff involved in ongoing care still only considered to be knowledgable by about 40%!

Health care teams need to monitor research landscape.

Diagnosis

“Dare to think rare” – medical education tends to stifling curiosity. Proformas and pathways as a hindrance to rare conditions.

Eg crushing chest pain in 40yr old slim female – spontaneous coronay artery dissection!

GENES –

  • Group of congenital anomalies – 1 is common, 2+ less so
  • Extreme/exceptional presentation of common condition – eg infection, or child presentation of something seen normally in adults
  • Neurodevelopmental delay/regression – “bad behaviour”?
  • Extreme/exceptional pathology
  • Surprising lab results

History – trying not to ignore anything. 3 generation family history. Pregnancy loss; disability.

“THINK AND” – many stories of diagnosis only being made when someone listens to whole story from beginning to end. Parental concerns AND multisystem problems AND family history AND disability… Example of Alstrom syndrome – visual impairment then obesity, then heart failure.

“THINK AGAIN” – beware diagnostic bias of having a diagnosis from the past or from another doctor. “Momentum bias” – diagnosis might start as tenuous but become entrenched. “Premature closure” – thinking stops when diagnosis accepted (even if not verified). New test available to confirm?

Open access tools – www.FindZebra.com, OMIM, Orphanet. Only Google after trying these! Start with 2 most specific (stand out) terms. [Phenomizer appears to be defunct]. Mendelian – AI tool in development.

NHS is at forefront of genomic medicine (whole genome analysis rather than panels of tests) – 100 000 genomes of people with rare disease and cancer analysed. Approx 1 in 4 rare disease patients have had useful (“actionable”) results.

Phenotypes are helpful but same pathway can be affected by different mutations and same phenotype can be seen in different conditions.

Microarray vs gene panel vs whole exome (coding only) vs whole genome…

Hope is for quicker diagnosis, less tests, less inappropriate treatment, support family planning decisions, enhance research.

National Genomic Test directory – https://www.england.nhs.uk/publication/national-genomic-test-directories/

Downside is variants of uncertain significance… https://vimeo.com/451887065

[Medics 4 Rare Diseases]

Neurofibromatosis

Autosomal dominant condition, so 50% risk of passing on to offspring and variable penetrance. May be spontaneous mutation.

Diagnosis still essentially clinical: 1988 Consensus is for any 2 of the following:

  • 6 or more cafe-au-lait spots (at least “pencil thickness” in diameter?)
  • axillary or groin freckling
  • 2 or more Lisch nodules – pigmented lesions in iris, may need slit lamp to see. No clinical consequence!
  • 2 or more neurofibromas,
  • optic pathway glioma (OPG),
  • bone dysplasia,
  • first-degree family relative with NF1 

Plexiform neurofibromas are larger ones with potential to cause visual, hearing, even cardiac problems.

Issues are:

  • High blood pressure
  • Epilepsy (lesions develop in brain)
  • Bone problems including scoliosis
  • Effects of neurofibromas in sensitive locations
  • Cosmetic appearance, self image
  • Cancer (malignant change in neurofibroma but also brain and breast)
  • Risk to own children

Ophthalmology review annually in children, every 2 yrs in adults, given risk of optic gliomas.

Family support at https://nervetumours.org.uk/

Clinical trial of selumetinib had beneficial effect on inoperable plexiform fibromas.

G6PD deficiency

Glucose 6 phosphate dehydrogenase deficiency. X-linked.

Can present with prolonged jaundice in babies. Otherwise with haemolysis (causing jaundice and anaemia).

Haemolysis triggered by infections, but also drugs and chemicals. Classically sulfonamides, but most relevant are:

  • Anti-malarials (ironically)
  • Nitrofurantoin!
  • Aspirin (so Kawasaki)
  • Henna! Other dyes
  • Moth balls!

Geographical risk areas –

Porphyria

Various types, all accumulate toxic levels of porphyrins in body but variable presentations.

Variegate Porphyria

The one associated with Dutch or Afrikaner (white South African) genetics. PPOX mutations

Specific symptoms can vary greatly; autosomal dominant so variable penetrance (can even be asymptomatic). Typically:

  • Photosensitivity
  • GI symptoms including abdominal pain, nausea, vomiting, constipation
  • Neurological: extremity pain, weakness, anxiety, restlessness and convulsions
  • Acute attacks, usually severe abdominal pain (can be chest), vomiting first. Then confusion, convulsions, and muscular weakness. Lasts days or weeks. Recovery from severe paralysis can be slow.

Triggers for acute attacks include drugs, hormones (especially progesterone), lack of carbohydrate intake, alcohol, and stress.

Diagnosis is by porphyrins in plasma, urine and stool.

Treatment now available – Panhematin is used to halt acute attacks and prevent attacks, Givlaari just for prevention.

Congenital cataracts

Differential:

  • Varicella
  • Rubella
  • CMV
  • Toxoplasmosis
  • HSV
  • Syphilis, HIV
  • Genetic non syndromic – various
  • Syndromes – Downs/Patau
  • X-linked Lowe syndrome (LD and proximal tubular dysfunction)
  • Autosomal dominant myotonic dystrophy (various eye problems), Neurofibromatosis type 2
  • Zellweger (includes neonatal adrenoleukodystrophy and infantile Refsum) – peroxisomal
  • Galactosaemia, Cockayne syndrome

Heterotaxy syndromes

A spectrum of disorders where the normal left-right arrangement of organs in the body is disturbed (“errors of lateralisation”).

Situs inversus is complete mirror image arrangement – there are no health consequences as a result (other than iatrogenic eg delayed diagnosis of appendicitis).

Many genetic causes. Primary cilial dyskinesia (Kartagener syndrome) is one.

Heart – IVC can be interrupted, requiring azygos veins to drain lower body vessels back to heart. Many variations of valves and connections seen. Congenital heart block often seen.

Gut – malrotation, biliary atresia

Asplenia or polysplenia.

Horseshoe or dysplastic kidneys.

Cowden syndrome

Autosomal dominant, PTEN gene (10q23). See OMIM.

Clinically –

  • Macrocephaly
  • Skin lesions – esp hamartomatous. Eg trichilemmomas (smooth, skin coloured, warty or dome like lesions, esp face), acral keratoses (ie on hands), papillomatous papules)
  • Increased risk for the development of breast, thyroid, and endometrial carcinoma

In some cases intestinal polyps, papilloedema, immunodeficiency.

Bartter’s syndrome

Abnormal renal excretion, leading to low potassium.

Presents in early childhood with failure to thrive. Could also be constipation, muscle cramps and weakness (potassium needed for membrane potential, so these are all neuromuscular) and non-specific dizziness and fatigue.

Characteristic hypokalemic, hypochloremic metabolic alkalosis. High plasma renin activity and high aldosterone concentration seen.

Gitelman syndrome is similar, less severe (distal tubule, rather than ascending limb of loop of Henle) – less failure to thrive, in fact often asymptomatic detected incidentally. Might present with nocturia/polyuria.

Urinary calcium excretion distinguishes the two syndromes. Bartter’s waste calcium (more severe, after all), Gitelman retain.

Treatment is with supplementation.

Decompensation can be precipitated by diarrhoea or vomiting. Acute treatment can include potassium-sparing diuretics (spironolactone), cyclo-oxygenase inhibitors and renin-angiotensin blockers.

Pseudo-Bartter’s is due to CF.

Fragile X

Cause of developmental delay.

FMR1 gene is on X chromosome, obviously, and is a trinucleotide repeat disorder (along with Friedrich’s ataxia, myotonic dystrophy, Huntington disease etc), so inheritance is interesting.

Dads can carry gene, but only pass it on to their daughters (who will all get it).

Mums will carry gene on 1 chromosome, so sons and daughters can both get it, but 50:50 chance.

As with other trinucleotide repeat disorders, gene expands with each generation, so risk of disease increases from 1 generation to the next, and this is somewhat predictable: intermediate gene (so 45-54 copies) won’t expand to cause disease (200+ copies) in 1 generation, but premutation gene (55-199) copies probably will.

Features:

  • Moderately severe learning disability
  • Facial features – long face, midface hypoplasia, large lips and jaw, small ears
  • Macro-orchidism

Females less severely affected, of course.