Category Archives: Genetics

Angelman syndrome

General paediatrics, Genetics, Neurology

Caused (mostly) by absence of maternal contribution to a region of the 15q chromosome.  Paternal uniparental disomy is one way this can happen, although mostly there is de novo maternal deletion.  The same region is also responsible for Beckwith-Wiedemann syndrome, but this syndrome is the result of a paternal deletion.

Characteristically “happy puppet” –

  • severe speech and language delay
  • learning disability and epilepsy
  • Movement disorder esp ataxia, also tremor, hyperreflexia
  • open mouthed expression, large mandible
  • Excitability, paroxysmal laughter

[https://www.omim.org/clinicalSynopsis/105830]

Hereditary spherocytosis

General paediatrics, Genetics, Haem/Oncology

One of the genetic red blood cell abnormalities that protects against malaria (cf sickle cell), as haemolysis shortens life span and potential for parasite reproduction.

Phenotype (severity) consistent within family, but very different between families. FH may be vague eg splenectomy, jaundice rather than awareness of underlying diagnosis…

Presentation

Anaemia, jaundice and splenomegaly classically. Splenomegaly is usually mild and there is no increased risk of rupture. Neonatal jaundice can be severe but does not predict severe disease! Severe cases (assessed when well, not during crises, only about 5%) can be transfusion dependent in first years of life (erythropoietin helpful) but not usually afterwards.

May present with parvovirus aplastic crisis (not just red cells; white cells and platelets often drop too) – only happens once.

Diagnosis by spherocytes on film, reduced MCV, high reticulocytes (but retics do not go up during aplastic crisis), unconj hyperbilirubinaemia, splenomegaly. There are other causes of spherocytes, and they can be seen in normal neonatal blood films.

Differential is autoimmune haemolytic anaemia, which is associated with acute viral infection (direct Coombs test usually positive). Osmotic fragility test does not distinguish, can be false negative in iron deficiency, and is unreliable in the first few months of life. New EMA dye binding test takes 2 hours and is 92% sensitive. Gene tests don’t add much.

Other problem is gallstones. High reticulocyte count predicts.

Folate probably only necessary for severe cases.

Splenectomy

Most children are asymptomatic, but severe cases can have growth failure, lethargy, heart failure and leg ulcers. Should be delayed until at least 5 yrs, potentially laparascopic and/or partial. Do cholecystectomy at same time if symptomatic. Platelets rise to abnormally high levels after splenectomy, but no apparent increase in thrombosis.

[Arch Dis Child PMID 15321852]

Autosomal dominant polycystic kidney disease

General paediatrics, Genetics, Renal

ADPKD – previously Adult PCKD but now recognized as having manifestations in childhood.  Cf Autosomal recessive disease, severe, renal failure in infancy.

1 in 400 to 1,000 live births, making it the most common monogenic cause of renal failure. The typical age of onset is in middle life, but the range is from infancy to 80 years.  Associated with liver cysts (asymptomatic) and intracranial aneurysms. 10-25% do not have family history (de novo mutations, missing records or mosaicism).

Possible presenting symptoms of renal disease in children with ADPKD are frequency, nocturia and/or, hematuria, urinary tract infection(s) and back, flank or abdominal pain. Often, the earliest symptoms are polyuria and polydipsia, from decreased urinary concentrating ability.

Extrarenal manifestations seen esp hypertension (renin angiotensin system, sodium retention, endothelial dysfunction), also liver cysts (asymptomatic), intracranial cysts and valvular defects but these are only seen in adults. 25% of children are hypertensive by the time they reach adolescence.  (GFR stays stable until around 40yrs, then rapid decline, about 50% have ESRF by 60yrs).

Importantly, children who were diagnosed in utero or within their first 18 months of life, the so-called VEO group, represent a particularly high-risk group of ADPKD patients and should be managed accordingly.  Diagnostic imaging criteria not validated under 15yrs, genetic testing also challenging.

Recommendation from Kidney Disease Improving Global Outcomes (KDIGO) Consortium against screening children for APCKD.  [Also highlight variety of different cystic disorders in children, so recommend thorough clinical assessment for extrarenal manifestations in case syndrome eg Von Hippel Lindau, USS of parents and/or grandparents if negative family history, and USS to look for dysplastic kidneys, glomerulocystic disease, and tuberous sclerosis complex].[Kidney international 2015]

Increasing evidence that hypertension, left ventricular hypertrophy (even between 75th and 95th centile for BP) and increased kidney volume predates symptoms in affected children.  A study of early use of ACE inhibitor halted progression of LVH and fall in renal function.  Adding pravastatin reduced progression of structural kidney disease.  Disease modifying drugs in development.  [BMJ 2016;353:i2957 Editorial, GOS, Birmingham, Evelina].  “We propose an urgent national debate on an improved inclusive approach involving patients and their families and a range of clinicians, ethicists, and commissioners. A few pounds spent now on screening and early intervention could save many thousands later by delaying hypertensive complications and chronic kidney disease.”

Potential for pre-implantation genetic diagnosis.  See Ethics.

Only one drug known to have moderate effect on disease progression in adult ADPKD patients, vasopressin V2 receptor antagonist tolvaptan (recent Cochrane review).  But timing of use unclear.

Psychological impact of having genetic disease that can be passed on to children very common in adult patients.  But a benefit of diagnosis is potential to target modifiable risk factors  – children with normal BP have slower cyst growth.  And knowledge can give sense of control over life decisions, esp reproductive decisions.

Turners syndrome

General paediatrics, Genetics

45XO but mosaics occur.

  • Short stature
  • facial naevi, sphinx like bright eyes
  • Webbed neck
  • Puffy hands and feet as baby
  • Cystic hygroma ie soft tissue mass in neck or intra-thoracic
  • Streak ovaries ie infertile
  • middle ear probs
  • learning difficulties – not really, but maths can be a problem

Multiple sclerosis

Genetics, Neurology

Only 3-5% of cases of MS have symptoms before the age of 16. Most have a relapsing-remitting course, particularly in the beginning, typically with one to two relapses per year. The frequency of attacks does seem to predict disease severity and earlier evolution to secondary progressive phase.

Although it takes longer in kids to develop persistent disability, they still develop it at a relatively young age, for example the third or fourth decade of life. That is of course going to have significant effects on life course, including work and family life.

Even at onset, cognitive function is often reduced, which will also affect education and socialisation. So clearly there is interest in disease modifying treatments.

Presentation in younger children often follows an infectious illness. Cognitive impairment is more common relative to older kids.

Investigations

MRI of brain and spine, looking for demyelinating lesions.

Monoclonal bands in CSF.

Treatment

Steroids 10-30mg/kg for 3-5 days effective. No good evidence for IVIG. Where acute life threatening symptoms, plasmapheresis may be effective where steroids fail.

In adults good evidence for interferon Beta in relapsing-remitting disease, IM or SC depending on product, reduces relapse rate and probably slows progression of disability. Glatiramer is a synthetic product with similar effects.

Second line treatments in adults include Natalizumab, mitoxantrone and cyclophosphamide.

Differential diagnosis

  • lysosomal storage disorders,
  • various mitochondrial diseases,
  • other neurometabolic disorders,
  • Krabbe, Metachromatic leukodystrophy, X-linked adrenoleukodystrophy, Fabry, Niemann-Pick C, Chidak-Higashi.  [Clue is in the name, leukodystrophy]

Since these are genetic conditions, essential for management and genetic counselling.

J Weisfeld-Adams http://brain.oxfordjournals.org/content/138/3/517

Mitochondrial inheritance

Genetics

A mother with a mitochondrial DNA gene mutation will pass this abnormal gene to all of her children. The children will all be affected, but with different degrees of severity.

As it is not possible to predict how the children will be affected, this is immensely difficult for planning a family.

Leigh disease

General paediatrics, Genetics, Neurology

Infantile subacute necrotizing encephalopathy.

Clinically heterogenous, lots of different genes.  Can be X-linked, mitochondrial or recessive!!!  Main genetic problem is mitochondrial complex defect, but same disease can be caused by pyruvate dehydrogenase defect (actually a complex of enzymes).

Baby’s initial development may appear normal, although there may be failure to thrive.  Lactate can be raised in serum.  Progressive, often rapid, neurological deterioration including hypotonia, dystonia, seizures.

Lesions (necrotic, gliosis, spongiosis) seen in basal ganglia, brainstem, cerebellum, spinal chord.  CSF lactate and pyruvate may be raised, even if serum normal.

See mitochondrial inheritance.

 

Atypical HUS

General paediatrics, Genetics, Haem/Oncology, Renal

Most Haemolytic Uraemic Syndrome is associated with a diarrhoeal illness (D+ HUS), esp E coli O157.

Atypical HUS is a bad name for HUS that develops in certain individuals due to a genetic, complement disorder.  Disease is typically triggered by infection, esp respiratory tract, else diarrheal illness in 80% of pediatric forms.

Consider in young infants (less than 5% of D+HUS cases occur before the age of 6 mo), severe cases, non-colitis.

The penetrance of the disease among carriers of mutations in CFH, CFI and MCP genes is approximately 50%-60%.

Low C3 levels are a clue (seen with mutations in CFH, CFI and MCP).  In almost all cases of aHUS C4 levels are normal. Normal C3 levels do not however exclude a mutation.  Check factor H and factor I too.

Diagnosis

Measure CFH, CFI and MCP levels using radio-immune-diffusion assay (RIDA) or FACS. This however fails to detect low protein levels in 25%-75% of mutations, so genetic analysis also needed.

Check ADAMTS13 activity (as seen in thrombotic thrombocytopaenic Purpura, TTP) as part of differential.

Make sure you have enough blood samples before plasma exchange!

In neonates, screen for defective cobalamin metabolism (excess homocystine and methylmalonate in urine ).  These babies have high mortality from multiorgan failure, a prompt diagnosis and B12 supplementation is their only hope.

Beckwith Wiedemann Syndrome

Genetics, Metabolic, Neonatology

Chromosome 11p problem, where IGF2 gene lies. Hemihypertrophy, macroglossia, ear creases/pits, exomphalos, umbilical hernia, visceromegaly, macrosomy, hyperinsulinism.

Focal disease is associated with uniparental disomy in chromosome 11 (“upd(11)pat”), whereas diffuse disease can be familial or sporadic.

Focal disease can be managed by limited surgery, whereas diffuse disease needs near total pancreatectomy for any benefit. DOPA-PET scans can differentiate focal disease with a sensitivity of 88-94%, and are 100% accurate in localizing the focal lesion (Aberdeen does).

At increased risk of tumours esp nephroblastoma, adrenal carcinoma, hepatoblastoma. Screening recommendations depend on mutation viz IC2 LOM, IC1 GOM, upd(11)pat etc. For all but the first, every 3 months until age 7yrs.

OMIM link.

Support group https://www.bwssupport.com/

Congenital Hyperinsulinism

Congenital, Genetics, Metabolic, Neonatology

Hyperinsulinaemic hypoglycaemia is a common cause of persistent severe hypoglycaemia, and is associated with long term neurodisability and epilepsy. Can be congenital, due to unregulated beta cell function (used to be called nesidioblastosis), else secondary to various other conditions eg:

  • Maternal diabetes mellitus
  • Birth asphyxia
  • IUGR
  • Beckwith Wiedemann Syndrome – about 50% are affected, usually transiently
  • Inborn error of metabolism eg glycosylation disorder

Can present with severe hypoglycaemia in the newborn period despite good oral intakes, else more insidiously in infancy and childhood. No ketones of course – cf ketotic hypoglycaemia.  Macrosomia (+/- hypertrophic cardiomyopathy and hepatomegaly) is a feature of fetal hyperinsulinism but is not always present, otherwise typical features of hypoglycaemia may be seen, including seizures.

Cases secondary to IUGR/asphyxia tend to be transient, settling within a few days, but some have persistent symptoms for months before suddenly resolving!

Recessive defects in sulphonylurea receptor probably most common cause.  Fasting or exertion are the usual triggers, but postprandial symptoms may reflect dumping syndrome (usually secondary to gastro-oesophageal surgery) or else hyperammonaemic hyperinsulinism (glutamate dehydrogenase disorder – the high ammonia of 100-200 is persistent but asymptomatic). A form of exercise induced hyperinsulinism exists that requires exercise testing to diagnose.

Insulinoma is more likely in later childhood. Can be part of a multiple endocrine neoplasia syndrome type 1 (ask family history).

Raised plasma hydroxybutyrylcarnitine and urinary 3-hydroxyglutarate are diagnostic of Hydroxy AcylCoA Dehydrogenase (HADH) deficiency.

Management aims to achieve normal glucose levels, using Carbohydrate supplemented oral feeds plus IV fluids. A central line may be needed to give concentrated dextrose solutions, esp if chubby. Glucagon can be given IM in an emergency but may lead to paradoxical insulin release. Glucagon and/or octreotide can be given as infusions in resistant cases.

For ongoing treatment, diazoxide acts on K-ATP channels in beta cells. Chlorthiazide is synergistic in the neonatal period. Hypertrichosis is the main side effect of diazoxide. Some rare gene defects are resistant to Diazoxide! Feeding probs esp GORD common, partly due to all the NG/IV feeding.

[Kapoor, Arch Dis Child 2009 PMID 19193661]