ALAGILLE SYNDROME

Alagille Syndrome — a multisystem disorder affecting bile ducts, heart, skeleton, and eyes, where the first targeted therapy (maralixibat) was approved in 2021 and molecular confirmation guides both treatment eligibility and prognosis.

Whole genome sequencing evaluates both JAG1 and NOTCH2 — including the large deletions that account for 7% of JAG1 cases — providing the molecular diagnosis that standard sequencing-only panels may miss.

JAG1
NOTCH2

About this condition

Alagille Syndrome

Alagille syndrome (ALGS) is an autosomal dominant multisystem disorder caused by pathogenic variants in JAG1 (~97% of cases, chromosome 20p12.2) or NOTCH2 (~2-3%, chromosome 1p12). JAG1 encodes a ligand in the Notch signaling pathway, which is critical for cell fate determination during embryonic development of bile ducts, heart, vasculature, skeleton, and eyes. Over 600 different JAG1 pathogenic variants have been reported, including missense, nonsense, frameshift, splice site variants, and whole-gene or multi-exon deletions (~7% of cases). ALGS affects approximately 1 in 30,000-50,000 births.

The cardinal features are bile duct paucity (intrahepatic cholestasis with severe pruritus, jaundice, and xanthomas), congenital heart defects (peripheral pulmonic stenosis in ~90%, complex cardiac defects in ~15%), butterfly vertebrae on spine radiographs, posterior embryotoxon on ophthalmological exam, and a characteristic facial appearance (prominent forehead, pointed chin, deep-set eyes). Clinical severity is highly variable — even within the same family carrying the identical JAG1 variant — ranging from subclinical liver involvement to liver failure requiring transplantation in approximately 15-20% of patients.

Maralixibat (Livmarli), an ileal bile acid transporter (IBAT) inhibitor, was approved by the FDA in 2021 for the treatment of cholestatic pruritus in Alagille syndrome patients aged 1 year and older. It reduces serum bile acid levels and significantly improves the debilitating pruritus that impairs quality of life. Odevixibat (Bylvay) is approved for progressive familial intrahepatic cholestasis (PFIC) and is under investigation for ALGS. Liver transplantation remains necessary for patients with progressive liver failure or intractable pruritus despite medical therapy.

Approximately 50-70% of ALGS cases are de novo — parents are unaffected. However, because of variable expressivity, apparently unaffected parents should be evaluated for subtle features (posterior embryotoxon, butterfly vertebrae) before concluding de novo status.

Gene locus: JAG1 (20p12.2), NOTCH2 (1p12)

JAG1 whole-gene deletions account for 7% of Alagille syndrome and are missed by exon-sequencing panels. Whole genome sequencing detects both sequence variants and structural rearrangements in a single test.

7% of JAG1 pathogenic alleles are whole-gene or multi-exon deletions invisible to standard sequencing

Approximately 7% of Alagille syndrome patients carry large JAG1 deletions — ranging from single-exon to whole-gene deletions and occasionally extending into flanking genes. Standard Sanger sequencing or exon-only NGS panels do not detect copy number changes, returning a false-negative result in these patients. When a patient meets clinical criteria for ALGS but sequencing of JAG1 is negative, MLPA or chromosomal microarray must be ordered separately. Whole genome sequencing detects both sequence variants and copy number variants from the same data, eliminating this diagnostic gap and the associated time delay.

Molecular diagnosis enables cardiac surveillance planning — 15% of ALGS patients have complex heart defects requiring intervention

While peripheral pulmonic stenosis (present in ~90% of ALGS patients) is generally benign and often resolves with growth, approximately 15% of ALGS patients have complex congenital heart defects — tetralogy of Fallot, pulmonary atresia, ventricular septal defects — requiring surgical intervention. Cardiac evaluation is standard of care for all newly diagnosed ALGS patients. Molecular confirmation in an infant presenting with neonatal cholestasis triggers complete cardiac workup before the heart defect presents clinically. Without molecular diagnosis, cholestatic infants may be evaluated solely for biliary disease, missing concurrent cardiac pathology.

Alagille Syndrome — a multisystem disorder affecting bile ducts, heart, skeleton, and eyes, where the first targeted therapy (maralixibat) was approved in 2021 and molecular confirmation guides both treatment eligibility and prognosis.

Alagille Syndrome

JAG1 whole-gene deletions account for 7% of Alagille syndrome and are missed by exon-sequencing panels. Whole genome sequencing detects both sequence variants and structural rearrangements in a single test.

7% of JAG1 pathogenic alleles are whole-gene or multi-exon deletions invisible to standard sequencing

Molecular diagnosis enables cardiac surveillance planning — 15% of ALGS patients have complex heart defects requiring intervention

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